FEL2014 - List of Keywords (undulator)

Paper	Title	Other Keywords	Page
MOA03	First Lasing at FLASH2	electron, operation, photon, laser	7
	S. Schreiber, B. Faatz DESY, Hamburg, Germany
	FLASH, the free-electron laser user facility at DESY (Hamburg, Germany), has been upgraded with a second undulator beamline FLASH2. The installation of the FLASH2 electron beamline, including twelve variable gap undulators, was finalized early 2014, and beam commissioning of the new beamline started in March 2014. We announce first lasing at FLASH2 achieved at a wavelength of 40 nm on August 20, 2014.
	Slides MOA03 [3.896 MB]

MOB01	Pulse Control in a Free Electron Laser Amplifier	FEL, electron, radiation, laser	9
	L. Giannessi ENEA C.R. Frascati, Frascati (Roma), Italy
	Funding: Work supported by MIUR (DM1834 RIC.4-12-2002 and Grants No. FIRB- RBAP045JF2 and No. FIRB-RBAP06AWK3), and by the EU Commission in the Sixth Framework Program, Contract No. 011935- EUROFEL. A significant progress has been made in controlling the properties of the radiation emitted by a FEL amplifier. Experiments have demonstrated the possibility both to increase the temporal coherence and to reduce the amplifier length to reach saturation, by seeding it with an external source. This may be a solid state, short pulse, laser (Ti:Sa,OPA..), doubled or tripled in a crystal, or a high order harmonic pulse generated in gas. The coherence improvement and the increased compactness of the source are only the first beneficial offspring of this marriage between the optical laser world and that of FELs. Non-linear effects in the seeded FEL dynamics may be exploited to shorten the pulse length beyond that allowed by the FEL natural gain bandwidth. Multiple seed pulses can be used to generate pulses whose temporal distance and properties are also controlled. Similarly, the FEL gain can be adapted to match the seed properties by tailoring the electrons phase space to generate ultra-short output pulses at unparalleled intensities. I had the honor (and luck) to participate in many relevant experiments at the SPARC and FERMI FELs and I will give my personal overview.
	Slides MOB01 [29.932 MB]

MOP003	Helical Undulator Radiation in Internally Coated Metallic Pipe	radiation, vacuum, synchrotron-radiation, impedance	26
	T.L. Vardanyan, A. Grigoryan, L.V. Hovakimyan, M. Ivanyan, A.V. Tsakanian, V.M. Tsakanov CANDLE SRI, Yerevan, Armenia
	The vacuum chambers of many advanced undulator sources are coated internally in order to reduce the impedance of the vacuum chamber or improve the vacuum performance. Although the impedances and radiation properties of the internally coated metallic pipes for straightforward moving charge are well studied, the peculiarities of the particles wiggling motion on the radiation characteristics in such structure are missed. In this paper we obtain exact expressions for the fields of a particle moving along a spiral path, as in the single-layer resistive as well as in the two-layer metallic waveguides, modelling NEG coating of the waveguide walls. Based on these results, it will be possible to obtain the necessary characteristics of the radiation of helical undulators, very close to reality. The solution is obtained as a superposition of a particular solution of inhomogeneous Maxwell's equations in a waveguide with perfectly conducting walls, and the solutions of the homogeneous Maxwell equations in the single-layer and double-layer resistive waveguides. Solution in the form of the multipole expansion for inhomogeneous Maxwell's equations for a waveguide with perfectly conducting walls, are also obtained in this study.

MOP007	High Accuracy Shimming Technique for the Phase Shifters of the European XFEL	operation, simulation, permanent-magnet, electron	29
	Y. Li DESY, Hamburg, Germany J. Pflüger XFEL. EU, Hamburg, Germany
	For the European XFEL 91 phase shifters are needed, which have to fulfil stringent field integral specifications: There should be no observable beam deflection when the strength, i.e. the magnetic gap is changed In order to facilitate the mass production of 91 phase shifters within the tough XFEL schedule a shimming technique was developed. It is based on measured shim signatures and is straight forward and fast to apply. The method is described and results are presented demonstrating that all requirements can be fulfilled.

MOP008	Temperature Effects of the FLASH2 Undulators	controls, operation, feedback, insertion-device	34
	M. Tischer, A. Schöps, P. Vagin DESY, Hamburg, Germany
	FELs are very sensitive to small changes in the resonance condition of the emitted radiation. As a consequence, permanent magnet undulators in FELs usually require extensive temperature control in order to assure stable operation conditions. In principle, the temperature dependence of permanent magnet material is well known but more things need to be considered like different thermal expansion of various mechanical parts or thermally induced deformation which do not only affect the K parameter but also the field quality. We have performed temperature dependent magnetic measurements in a range from 19 to 28 degrees Celsius and have analyzed the magnetic performance of the undulator. The results of this case study can be transferred to all FLASH2 undulators and shall allow for a simple temperature dependent gap correction in order to make the spectral properties insensitive to temperature changes of the insertion devices.

MOP012	Implementation Phase of the European XFEL Photon Diagnostics	photon, diagnostics, FEL, electron	41
	J. Grünert, J. Buck, F. Dietrich, W. Freund, A. Koch, M. Planas XFEL. EU, Hamburg, Germany
	The European XFEL facility with 3 undulators and initially 6 experimental end-stations requires an extensive set of photon beam diagnostics for commissioning and user operation, capable of handling the extreme brilliance and its inherent damage potential, and the high intra bunch train repetition rate of 4.5MHz, potentially causing additional damage by high heat loads and making shot-to-shot diagnostics very demanding [1]. After extensive design [2-4] and prototype studies, in 2014 the installation of the photon beam devices starts with the equipment in the first photon tunnel XTD2 which is where the SASE1 hard X-ray undulator is located. This contribution reports on the device construction progress by focusing on the XTD2 tunnel devices and their implementation into the tunnel environment. [1] J.Grünert, Framework for X-Ray Photon Diagnostics at the European XFEL, TR-2012-003, 04/2012 [2] J.Buck, Online Photoemission Time-of-Flight Spectrometer for X-ray Photon Diagnostics, TR-2012-002, 06/2012 [3] C.Ozkan, Conceptual design report for Imaging Stations at the European XFEL, TR-2012-004, 02/2012 [4] W.Freund, The European XFEL Undulator Commissioning Spectrometer, XFEL. EU 05/2011

MOP018	Conceptual Study of a Self-seeding Scheme at FLASH2	FEL, electron, simulation, photon	53
	T. Plath, L.L. Lazzarino Uni HH, Hamburg, Germany K.E. Hacker DELTA, Dortmund, Germany
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K1GU4 and 05K10PE1 and the German Research Foundation program graduate school 1355. We present a conceptual study of a self-seeding installation at the new FEL beamline, FLASH2, at the free-electron laser at DESY, Hamburg. For self-seeding, light from a first set of undulators is filtered by a monochromator and thus acts as a seed for the gain process in the main undulator. This scheme has been tested at LCLS at SLAC with a diamond monochromator for hard X-rays and with a grating monochromator for soft X-rays covering energies between 700 and 1000 eV. For such a design to offer benefits at FLASH2, it must be modified to work with X-rays with wavelength of about 5 nm (248 eV) where the damage threshold of the monochromator in the setup and the divergence at longer wavelengths become an issue. An analysis of the potential performance and limitations of this setup is performed using GENESIS 1.3 and a method developed for the soft X-ray self-seeding experiment at the European XFEL. With a total of 9 undulators in the first stage and 8 undulators after the monochromator, a pulse energy contrast ratio of 4.5 was simulated with an initial peak current of 2.5 kA.

MOP023	Development of a Magnetic System to Cancel the Attractive Force toward Structural Reform of Undulators	multipole, experiment, vacuum, synchrotron	75
	R. Kinjo, T. Tanaka RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan A. Kagamihata, T. Seike JASRI/SPring-8, Sayo-gun, Japan S. Yamamoto KEK, Tsukuba, Japan
	As part of a development on a compact and lightweight structure toward structural reform of undulators, cancellation of magnetic attractive force is being studied. Undulators usually require rigid mechanical components and frames to control the magnet gap precisely against the large attractive force in between. If the attractive force is canceled out near the point of load, the requirement for the undulator structure is relaxed and the cost and lead time of construction and installation are saved largely. For that purpose, we have proposed to add periodically-magnetized monolithic magnets beside the main magnets, which are expected to generate a repulsive force having the same gap-dependency as the attractive force in a cost-effective way. In the conference, the present status of the development of the force cancellation system will be presented, with a focus on the result of preliminary experiments using the periodically-magnetized magnets. Also introduced will be a development plan for the compact and lightweight undulator based on the cancellation system.

MOP028	Field Integral Measurement System and Optical Alignment System for HUST THz-FEL	FEL, alignment, electron, cavity	80
	B. Qin, Q.S. Chen, M. Fan, Q. Fu, T. Hu, X. Lei, K.F. Liu, X. Liu, P. Tan, Y.Q. Xiong, J. Yang, L. Yang HUST, Wuhan, People's Republic of China X. Liu, Z. Ouyang, Y.B. Wang Huazhong University of Science and Technology, State Key Laboratory of Advanced Electromagnetic Engineering and Technology,, Hubei, People's Republic of China Y.J. Pei USTC/NSRL, Hefei, Anhui, People's Republic of China
	A Free Electron Laser oscillator with radiation wavelength 50–100 μm is under construction in Huazhong University of Science and Technology (HUST). The linear polarization undulator with K=1.0-1.25 has been designed and manufactured by Kyma s.r.l., by using a pure permanent magnet scheme. Acceptance test bas been performed in Kyma factory with well controlled phase error and field integrals for all gaps. This paper introduces the development of an online field integrals measurement system for the undulator, using the stretched wire method. The design and considerations of the optical alignment system is described as well.

MOP030	Performance Analysis of Variable-Period Helical Undulator with Permanent Magnet for a KAERI THz FEL	permanent-magnet, FEL, radiation, simulation	84
	J. Mun, K.H. Jang, Y.U. Jeong, K. Lee, S. H. Park, N. Vinokurov KAERI, Daejon, Republic of Korea M.Y. Jeon Chungnam National University, Daejoen, Republic of Korea
	Funding: This work was supported by the World Class Institute Program of the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT and Future Planning.(NRF Grant Number:WCI2011-001) We realized a variable-period permanent-magnet helical undulator with high (~1 T) field amplitude, which is almost constant over undulator periods of 23–26 mm. Each undulator period has 4 modular sections of iron poles and permanent magnets embedded in non-magnetic disks with holes along the undulator axis. Modular plates undergo a longitudinal repulsive force from the magnetic field pressure and the spring coils between modular plates. The undulator period can thus be controlled by mechanically changing of the end plate longitudinal position. This compact design is suitable for a table-top terahertz free electron lasers. The measured on-axis field is about 0.97 T with the deviation less than 1% through the whole range of the undulator period variation. The measured spread of the longitudinal coordinates of the undulator field component maxima is less than 1%, and the measured field distribution meets the requirement for our terahertz FEL. The field reproducibility was checked by six measurements of the undulator field after the period variation for the 26 mm period. The r. m. s. phase errors is 3.7 degrees.

MOP033	Design, Fabrication, and Performance Tests of Dipole and Quadrupole Magnets for PAL-XFEL	quadrupole, dipole, multipole, optics	90
	H.S. Suh, M.-H. Cho, S.-H. Jeong, Y.-G. Jung, H.-S. Kang, D.E. Kim, I.S. Ko, H.-G. Lee, S.B. Lee, B.G. Oh, K.-H. Park PAL, Pohang, Kyungbuk, Republic of Korea
	PAL-XFEL is now being constructed in Pohang, Korea. This facility will consist of a 10 GeV linac and five undulator beamlines. As the first phase we will construct one hard X-ray and one soft X-ray beamlines which require 7 different families of dipole magnets, and 11 families of quadrupole magnets. We are designing these magnets with considering the efficient manufacturing and the proper power supplies. In this presentation, we describe the design features of the magnets, the manufacturing, and the thermal analysis with the test results.

MOP036	Estimating Effect of Undulator Field Errors using the Radiation Hodograph Method	radiation, electron, synchrotron-radiation, free-electron-laser	93
	N.A. Sokolov Budker INP & NSU, Novosibirsk, Russia N. Vinokurov BINP SB RAS, Novosibirsk, Russia
	Spatially-periodic magnetic structures are widely used for generation of high-brilliance radiation in storage rings, sources of synchrotron radiation and free electron lasers. In 1947, V.L. Ginzburg suggested the first undulator scheme. An alternating magnetic field created by a planar undulator makes electrons oscillate in the transverse direction, with interference of radiation emitted from separate parts of the trajectory. The spectrum of the forward emitted radiation is enchanced due to constructive interference. The ondulator is made of the magnetized bars that are not perfect and their magnetization differs. Therefore, the electron trajectory is not purely sinusoidal and, as a result, the spectral intensity fades. The task was to find out if the precision of magnet manufacturing is sufficient. This paper presents modelling of electron motion in the measured magnetic field of the new (third) free electron laser at the Siberian Synchrotron Radiation Centre. We have managed to estimate the effect of the field errors through comparison of the resulting emitted field amplitude with the amplitude from ideal magnet bars using the hodograph method.

MOP037	Modeling and Design of the Variable Period and Pole Number Undulator for the Second Stage of the Novosibirsk FEL	FEL, simulation, permanent-magnet, electron	96
	I. Davidyuk NSU, Novosibirsk, Russia O.A. Shevchenko, V.G. Tcheskidov, N. Vinokurov BINP SB RAS, Novosibirsk, Russia N. Vinokurov KAERI, Daejon, Republic of Korea
	The concept of the permanent magnet variable period undulator (VPU) has been proposed just several years ago and there are few examples of its implementation yet. The VPUs have several advantages compared to conventional undulators. One of them is wider radiation wavelength tunability range and another one is an option to increase the number of poles for shorter periods. Both these advantages will be realized in VPU which is being developed now at Budker INP. In this paper we present the 2-D and 3-D magnetic field simulation results and discuss the design features of this VPU.

MOP038	Characterization of the Undulator Magnetic Field Quality by the Angle Averaged Radiation Spectrum	radiation, electron, photon	100
	O.A. Shevchenko, N. Vinokurov BINP SB RAS, Novosibirsk, Russia N. Vinokurov KAERI, Daejon, Republic of Korea
	The real undulator magnetic field always contains errors which influence undulator performance. The effect of these errors is usually characterized by broadening of the spontaneous emission spectrum at zero angle and corresponding reduction of the spectral intensity. This approach works very well for the phase errors while it does not take into account transversal trajectory displacements. The integrated over the angles radiation spectrum contains more complete information about the undulator field quality but its calculation requires more effort. Therefore the spectral density of emitted radiation (the total number of emitted photons with given energy) can be considered as a figure of merit for an undulator. In this paper we derive analytical formula for this spectrum suitable for doing efficient numerical calculations and demonstrate its application to the case of some typical undulator field errors.

MOP040	General Strategy for the Commissioning of the ARAMIS Undulators with a 3 GeV Electron Beam	electron, alignment, quadrupole, photon	107
	M. Calvi, M. Aiba, M. Brügger, S. Danner, R. Ganter, R. Ischebeck, L. Patthey, T. Schietinger, T. Schmidt PSI, Villigen PSI, Switzerland
	The commissioning of the first SwissFEL undulator line (Aramis) is planned for the beginning of 2017. Each undulator is equipped with a 5-axis camshaft system to remotely adjust its position in the micrometer range and a gap drive system to set K-values between 0.1 and 1.8. In the following paper the beam-based alignment of the undulator with respect to the golden orbit, the definition of look-up tables for the local correction strategy (minimization of undulator field errors), the fine-tuning of the K-values as well as the setting of the phase shifters are addressed. When applicable both electron beam and light based methods are presented and compared.

MOP041	Summary of the U15 Prototype Magnetic Performance	vacuum, electron, quadrupole, photon	111
	M. Calvi, M. Aiba, M. Brügger, S. Danner, R. Ganter, C. Ozkan, T. Schmidt PSI, Villigen PSI, Switzerland
	The first undulator prototype (U15) was assembled and magnetically tested. The instrumentation and the algorithms developed for the undulator optimization are presented and a comparison among different approaches is reviewed. The magnetic measurement results before and after the installation of the vacuum components are discussed. The summary of the undulator test with 100 MeV electron beam is presented and the impact of the radiation on the magnetics is addressed.

MOP043	Magnetic Design of an Apple III Undulator for SwissFEL	vacuum, polarization, operation, alignment	116
	T. Schmidt, A. Anghel, P. Boehler, M. Brügger, M. Calvi, S. Danner, P. Huber, A. Keller, M. Locher PSI, Villigen PSI, Switzerland
	In the frame of the SwissFEL project a soft x-ray line is planned in the coming years to cover the wavelength between 0.7 and 7.0nm. Based on the good experience at the SLS storage ring with Apple undulator as source of variable polarized light, Apple III type undulators are also foreseen at the SwissFEL. In this paper the design of these devices is introduced and the preliminary magnetic configuration together with the optimization strategy is presented in details.

MOP045	Phase Shifter Design for iSASE	electron, power-supply, FEL, simulation	123
	S.D. Chen, K. Fang, H.-D. Nuhn, C. Pellegrini, J. Wu, L. Zhu SLAC, Menlo Park, California, USA S.D. Chen, C.-S. Hwang NCTU, Hsinchu, Taiwan K. Fang Indiana University, Bloomington, Indiana, USA C.-S. Hwang NSRRC, Hsinchu, Taiwan
	A phase shifter to generate an additional phase advance of the spontaneous light versus the electron beam was de- signed for the iSASE scheme. The iSASE mechanism is for reducing the bandwidth further from SASE FEL process. A large phase advance about 1600*2Pi as the FEL operating at wavelength 0.8 nm was needed according to the simulation of iSASE process. Since the iSASE is thought to implement into LCLS II project, the space limitation causing by LCLS II should be considered when designing the phase shifter. An optimized three-pole electric phase shifter with 7.3 mm gap has the center field of 1.8 T . The vanadium steel was considered as pole material and the magnet physical length is 260 mm, meanwhile the water-cooling type copper coil was adopted. The temperature increment, force analysis, low field operation mode concept, and preliminary tolerance study were discussed.

MOP046	Undulator Radiation Damage Experience at LCLS	radiation, electron, operation, experiment	127
	H.-D. Nuhn, R.C. Field, Yu.I. Levashov, X.S. Mao, M. Santana-Leitner, J.J. Welch, Z.R. Wolf SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515 The SLAC National Accelerator Laboratory has been running the Linac Coherent Light Source (LCLS), the first x-ray Free Electron Laser since 2009. Undulator magnet damage from radiation, produced by the electron beam traveling through the 133-m long straight vacuum tube, has been and is a concern. A damage measurement experiment has been performed in 2007 in order to obtain dose versus damage calibrations. Radiation reduction and detection devices have been integrated into the LCLS undulator system. The accumulated radiation dose rate was continuously monitored and recorded. In addition, undulator segments have been routinely removed from the beamline to be checked for magnetic (50 ppm, rms) and mechanic (about 0.25 μm, rms) changes. A reduction in strength of the undulator segments is being observed, at a level, which is now clearly above the noise. Recently, potential sources for the observed integrated radiation levels have been investigated. The paper discusses the results of these investigation as well as comparison between observed damage and measured dose accumulations and discusses, briefly, strategies for the new LCLS-II upgrade, which will be operating at more than 300 times larger beam rate.

MOP047	A 200 μm-period Laser-driven Undulator	laser, electron, plasma, alignment	131
	F. Toufexis, T. Tang, S.G. Tantawi SLAC, Menlo Park, California, USA
	Funding: This project was funded by U.S. Department of Energy under Contract No. DE-AC02-76SF00515 and the DARPA AXiS program. To reduce the linac energy required for a given synchrotron radiation wavelength, and hence the size of the device, a smaller undulator period with sufficient field strength is needed. In this work, a microfabricated, laser-driven undulator with 200um undulator period is proposed. A TE wave that co-propagates with the electron beam is excited between two polysilicon thin films, having a gap of 16.5um. The mode that is excited is a deflecting mode and causes the electron beam to wiggle. The device is fabricated on a silicon wafer, using conventional silicon micromachining techniques. A single polysilicon thin film is supported on a silicon chip, which has a slit from the back to allow delivery of the laser beam. Two such chips are bonded together to form a 16.5um gap, within which the electron beam passes through. The final device has dimensions 1cm x 1cm x 1.1mm and has approximately 35 undulator periods. In this paper, the model, design, fabrication, and cold measurements of the device are reported.

MOP052	Update on FEL Performance for SwissFEL	FEL, simulation, radiation, emittance	140
	E. Prat, S. Reiche PSI, Villigen PSI, Switzerland
	The SwissFEL project under construction at the Paul Scherrer Institute foresees for 2017 the realization of an X-ray FEL with a photon wavelength down to 1 Å. In this paper we present the expected SASE performance for SwissFEL based on input distributions obtained from detailed start-to-end simulation results. The effects of the longitudinal wakefields due to resistive wall and surface roughness in the undulator beamline have been taken into account. We have studied and optimized the impact on the FEL performance of different factors like the electron focusing or the undulator tapering. Results for the standard cases with 200 pC and 10 pC electron bunch charge are shown.

MOP053	SASE FEL Performance at the SwissFEL Injector Test Facility	FEL, electron, simulation, gun	144
	S. Reiche PSI, Villigen PSI, Switzerland
	A 4 m long prototype of the SwissFEL undulator module with an undulator period length of 15 mm was installed at the SwissFEL Injector Test Facility and tested with a 200 MeV electron beam in the beginning of 2014. We observed FEL lasing in SASE mode in the wavelength range from 70 to 800 nm, tuning the wavelength by energy and gap. The measurements of the FEL performance are reported. on behalf of the SwissFEL Team

MOP054	Harmonic Lasing Options for LCLS-II	electron, photon, radiation, FEL	148
	G. Marcus, Y. Ding, Z. Huang, T.O. Raubenheimer SLAC, Menlo Park, California, USA G. Penn LBNL, Berkeley, California, USA
	Harmonic lasing can be a cheap and relatively efficient way to extend the photon energy range of a particular FEL beamline. Furthermore, in comparison to nonlinear harmonics, harmonic lasing can provide a beam that is more intense, stable, and narrow-band. This paper explores the application of the harmonic lasing concept at LCLS-II using various combinations of phase shifters and attenuators. In addition, a scheme by which individual undulator modules are tuned to amplify either the third or fifth harmonic in different configurations is presented in detail.

MOP055	Start-to-End Simulations for IR/THz Undulator Radiation at PITZ	electron, radiation, FEL, simulation	153
	P. Boonpornprasert, M. Khojoyan, M. Krasilnikov, F. Stephan DESY Zeuthen, Zeuthen, Germany B. Marchetti, E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany S. Rimjaem Chiang Mai University, Chiang Mai, Thailand
	High brightness electron sources for modern linac-based Free-Electron Lasers (FELs) have been characterized and optimized at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). Since the time structure of the electron bunches at PITZ is identical to those at the European XFEL, the PITZ accelerator is being considered as a proper machine for the development of an IR/THz source prototype for pump and probe experiments planned at the European XFEL. Tunable IR/THz radiation sources using synchrotron radiation from a dipole magnet, transition radiation, high gain FELs and coherent radiation of tailored or premodulated beams are currently under consideration. This work describes start-to-end simulations for generating the FEL radiation using an APPLE-II undulator with electron beams produced by the PITZ accelerator. Analysis of the physical parameter space has been performed with tools of the FAST program code package. Electron Beam dynamics simulations were performed by using the ASTRA code, while the GENESIS 1.3 code was used to study the SASE process. The results of these studies are presented and discussed in this paper.

MOP056	SASE Characteristics from Baseline European XFEL Undulators in the Tapering Regime	photon, electron, radiation, FEL	159
	I.V. Agapov, G. Geloni XFEL. EU, Hamburg, Germany G. Feng, V. Kocharyan, E. Saldin, S. Serkez, I. Zagorodnov DESY, Hamburg, Germany
	The output SASE characteristics of the baseline European XFEL, recently used in the TDRs of scientific instruments and X-ray optics, have been previously optimized assuming uniform undulators without considering the potential of undulator tapering in the SASE regime. Here we demonstrate that the performance of European XFEL sources can be significantly improved without additional hardware. The procedure consists in the optimization of the undulator gap configuration for each X-ray beamline. Here we provide a comprehensive description of the X-ray photon beam properties as a function of wavelength and bunch charge. Based on nominal parameters for the electron beam, we demonstrate that undulator tapering allows one to achieve up to a tenfold increase in peak power and photon spectral density in the conventional SASE regime.

MOP057	Proposal to Generate 10 TW Level Femtosecond X-ray Pulses from a Baseline Undulator in Conventional SASE Regime at the European XFEL	electron, laser, free-electron-laser, FEL	164
	E. Saldin, V. Kocharyan, S. Serkez, I. Zagorodnov DESY, Hamburg, Germany G. Geloni XFEL. EU, Hamburg, Germany
	Output characteristics of the European XFEL have been previously studied assuming an operation point at 5 kA peak current. Here we explore the possibility to go well beyond such nominal peak current level. We consider a bunch with 0.25 nC charge, compressed up to a peak current of 45 kA. An advantage of operating at such high peak current is the increase of the x-ray output peak power without any modification to the baseline design. Based on start-to-end simulations, we demonstrate that such high peak current, combined with undulator tapering, allows one to achieve up to a 100-fold increase in a peak power in the conventional SASE regime, compared to the nominal mode of operation. In particular, we find that 10 TW-power level, femtosecond x-ray pulses can be generated in the photon energy range between 3 keV and 5 keV, which is optimal for single biomolecule imaging. Our simulations are based on the exploitation of all the 21 cells foreseen for the SASE3 undulator beamline, and indicate that one can achieve diffraction to the desired resolution with 15 mJ (corresponding to about 3·10¹³ photons) in pulses of about 3 fs, in the case of a 100 nm focus at the photon energy of 3.5 keV.

MOP058	Purified SASE Undulator Configuration to Enhance the Performance of the Soft X-ray Beamline at the European XFEL	FEL, electron, radiation, laser	169
	V. Kocharyan, E. Saldin, S. Serkez, I. Zagorodnov DESY, Hamburg, Germany I.V. Agapov, G. Geloni XFEL. EU, Hamburg, Germany
	The purified SASE (pSASE) undulator configuration recently proposed at SLAC promises an increase in the output spectral density of XFELs. In this article we study a straightforward implementation of this configuration for the soft x-ray beamline at the European XFEL. A few undulator cells, resonant at a subharmonic of the FEL radiation, are used in the middle of the exponential regime to amplify the radiation, while simultaneously reducing the FEL bandwidth. Based on start-to-end simulations, we show that with the proposed configuration the spectral density in the photon energy range between 1.3 keV and 3 keV can be enhanced of an order of magnitude compared to the baseline mode of operation. This option can be implemented into the tunable-gap SASE3 baseline undulator without additional hardware, and it is complementary to the self-seeding option with grating monochromator proposed for the same undulator line, which can cover the photon energy range between about 0.26 keV and 1 keV.

MOP060	Demonstration of SASE Suppression Through a Seeded Microbunching Instability	electron, laser, FEL, free-electron-laser	177
	C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach Uni HH, Hamburg, Germany S. Ackermann, J. Bödewadt, G. Brenner, M. Dohlus, N. Ekanayake, T. Golz, E. Hass, K. Honkavaara, T. Laarmann, T. Limberg, E. Schneidmiller, N. Stojanovic, M.V. Yurkov DESY, Hamburg, Germany K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3 and the German Research Foundation programme graduate school 1355. Collective effects and instabilities due to longitudinal space charge and coherent synchrotron radiation can degrade the quality of the ultra-relativistic, high-brilliance electron bunches needed for the operation of free-electron lasers. In this contribution, we demonstrate the application of a laser-induced microbunching instability to selectively suppress the SASE process. A significant decrease of photon pulse energies was observed at the free-electron laser FLASH in coincidence with overlap of 800 nm laser pulses and electron bunches within a modulator located approximately 40 meters upstream of the undulators. We discuss the underlying mechanisms based on longitudinal space charge amplification [E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 110701 (2010)] and present measurements.

MOP061	Electron Beam Delays for Improved Temporal Coherence and Short Pulse Generation at SwissFEL	FEL, electron, radiation, simulation	181
	N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S. Reiche PSI, Villigen PSI, Switzerland
	Proposals have been made for the introduction of magnetic electron beam delays in between the undulator modules of a long sectional FEL undulator - these can be used for the generation of trains of FEL pulses which can individually be shorter than the FEL cooperation time [] or to greatly improve the temporal coherence of the FEL output compared to the nominal SASE configuration [,,]. This paper comprises a feasibility study of the application of these techniques to the SwissFEL hard X-Ray beamline. Three-dimensional simulations are used to investigate the potential photon output. [] N.R. Thompson and B.W.J. McNeil, PRL 100:203901, 2008. [] N.R. Thompson et al. In Proc IPAC2010, pages 2257–2259, 2010 [*] J. Wu, A. Marinelli, and C. Pellegrini. Proc FEL2012, 2012.

MOP062	FEL Proposal Based on CLIC X-Band Structure	linac, FEL, klystron, linear-collider	186
	A.A. Aksoy, O. Yavaş Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey E. Adli University of Oslo, Oslo, Norway D. Angal-Kalinin, J.A. Clarke STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom M.J. Boland, T.K. Charles, R.T. Dowd, G. LeBlanc SLSA, Clayton, Australia N. Charitonidis, A. Grudiev, A. Latina, D. Schulte, I. Syratchev, W. Wuensch CERN, Geneva, Switzerland G. D'Auria, S. Di Mitri Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy W. Fang, Q. Gu SINAP, Shanghai, People's Republic of China E.N. Gazis National Technical University of Athens, Athens, Greece M. Jacewicz, R.J.M.Y. Ruber, V.G. Ziemann Uppsala University, Uppsala, Sweden Z. Nergiz Nigde University, Nigde, Turkey
	A linear accelerating structure with an average loaded gradient of 100 MV/m at X-Band frequencies has been demonstrated in the CLIC study. Recently, it has been proposed to use this structure to drive an FEL linac. In contrast to CLIC the linac would be powered by klystrons not by an RF source created by a drive beam. The main advantage of this proposal is achieving the required energies in a very short distance, thus the facility would be rather compact. In this study, we present the structure choice and conceptual design parameters of a facility which could generate laser photon pulses below Angstrom. Shorter wavelengths can also be reached with slightly increasing the energy.

MOP064	Statistical Properties of the Radiation from SASE FEL Operating in a Post-saturation Regime with and without Undulator Tapering	FEL, radiation, free-electron-laser, laser	194
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	We describe statistical and coherence properties of the radiation from x-ray free electron lasers (XFEL) operating in the post-saturation regime. We consider practical case of the SASE3 FEL at European XFEL. We perform comparison of the main characteristics of X-ray FEL operating in the post-saturation regime with and without undulator tapering: efficiency, coherence time and degree of transverse coherence.

MOP065	Optimization of a High Efficiency FEL Amplifier	electron, FEL, radiation, laser	199
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	The problem of an efficiency increase of an FEL amplifier is now of great practical importance. Technique of undulator tapering in the post-saturation regime is used at the existing x-ray FELs LCLS and SACLA, and is planned for use at the European XFEL, Swiss FEL, and PAL XFEL. There are also discussions on the future of high peak and average power FELs for scientific and industrial applications. In this paper we perform detailed analysis of the tapering strategies for high power seeded FEL amplifiers. Application of similarity techniques allows us to derive universal law of the undulator tapering.

MOP066	An Overview of the Radiation Properties of the European XFEL	electron, radiation, operation, hardware	204
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	We present an overview of the radiation properties of the European XFEL based on recently accepted strategy of operation at the fixed set of electron energies (8.5 GeV, 12 GeV, 14 GeV, and 17.5 GeV), baseline parameters if the electron beam, and new set undulator parameters. We also discuss potential extension of the parameter space which does not require new hardware and can be realized at a very early stage of the European XFEL operation.

MOP067	Prospects for CW Operation of the European XFEL in Hard X-ray Regime	electron, linac, operation, FEL	210
	R. Brinkmann, E. Schneidmiller, J.K. Sekutowicz, M.V. Yurkov DESY, Hamburg, Germany
	The European XFEL will operate nominally at 17.5 GeV in SP (short pulse) mode with 0.65 ms long bunch train and 10 Hz repetition rate. A possible upgrade of the linac to CW (continuous wave) or LP (long pulse) modes with a corresponding reduction of electron beam energy is under discussion since many years. Recent successes in the dedicated R&D program allow to forecast a technical feasibility of such an upgrade in the foreseeable future. One of the challenges is to provide sub-Angstroem FEL operation in CW and LP modes. In this paper we perform a preliminary analysis of a possible operation of the European XFEL in the hard X-ray regime in CW and LP modes with the energies of 7 GeV and 10 GeV, respectively. We consider lasing in the baseline XFEL undulator as well as in a new undulator with a reduced period. We show that, with reasonable requirements on electron beam quality, lasing on the fundamental will be possible in sub-Angstroem regime. As an option for generation of brilliant photon beams at short wavelengths we also consider harmonic lasing that has recently attracted a significant attention.

MOP068	Suppression of the Fundamental Frequency for a Successful Harmonic Lasing in SASE FELs	FEL, electron, simulation, photon	215
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	Harmonic lasing in X-ray FELs has recently attracted a significant attention and is now seriously considered as a potential method for generation of brilliant photon beams at short wavelengths. It is clear, however, that for a successful harmonic lasing one has to suppress the fundamental. In this paper we discuss different methods for such a suppression: phase shifters, intraundulator spectral filtering, switching between the 3rd and the 5th harmonics etc.

MOP075	Laser Seeding Schemes for Soft X-rays at LCLS-II	laser, electron, bunching, radiation	223
	G. Penn LBNL, Berkeley, California, USA P. Emma, E. Hemsing, G. Marcus, T.O. Raubenheimer, L. Wang SLAC, Menlo Park, California, USA
	Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract Nos. DE-AC02-05CH11231 and DE-AC02-76SF00515. The initial design for LCLS-II incorporates both SASE and self-seeded configurations. Increased stability and/or coherence than is possible with either configuration may be provided by seeding with external lasers followed by one or more stages of harmonic generation, especially in the soft x-ray regime. External seeding also allows for increased flexibility, for example the ability to quickly vary the pulse duration. Studies of schemes based on high-gain harmonic generation and echo-enabled harmonic generation are presented, including realistic electron distributions based on tracking through the injector and linac.

MOP079	Generation of Multiple Coherent Pulses in a Superradiant Free-Electron Laser	electron, FEL, radiation, simulation	233
	X. Yang, S. Seletskiy BNL, Upton, Long Island, New York, USA L. Giannessi ENEA C.R. Frascati, Frascati (Roma), Italy
	We analyze the structure of the tail of a superradiant pulse, which is constituted by a train of sub-pulses with decaying amplitudes. We show how a trailing pulse, with pi phase advance from the leading pulse, is generated at the falling edge of the leading superradiant pulse, where the corresponding phase space is deeply saturated and the electrons become de-trapped by the reduced ponderomotive potential. Once the trailing pulse gains enough energy, it generates a second trailing pulse, and the process takes place again. By performing detailed simulations of the resulting electron phase space distribution and the FEL pulse spectral and temporal structure with PERSEO, we confirm that the deformation and re-bunching of the longitudinal phase space create a sequence of pulses. These results are compared to 3D simulations using the FEL code GENESIS 1.3 showing a good agreement.

MOP083	Start-to-End Simulation for FLASH2 HGHG Option	simulation, radiation, electron, FEL	244
	G. Feng, S. Ackermann, J. Bödewadt, W. Decking, M. Dohlus, Y.A. Kot, T. Limberg, M. Scholz, I. Zagorodnov DESY, Hamburg, Germany K.E. Hacker DELTA, Dortmund, Germany T. Plath Uni HH, Hamburg, Germany
	The Free-electron laser in Hamburg (FLASH) is the first FEL user facility to have produced extreme ultraviolet (XUV) and soft X-ray photons. In order to increase the beam time delivered to users, a major upgrade of FLASH named FLASH II is in progress. The electron beamline of FLASH2 consists of diagnostic and matching sections, a seeding undulator section and a SASE undulator section. In this paper, results from a start-to-end simulation for a FLASH2 High-Gain Harmonic Generation (HGHG) option are presented. For the beam dynamics simulation, space charge, coherent synchrotron radiation (CSR) and longitudinal cavity wake field effects are taken into account. In order to get electron beam bunches with small correlated and uncorrelated energy spread, RF parameters of the accelerating modules have been optimized as well as the parameters of the bunch compressors. Radiation simulations for the modulator and the radiator have been done with code Genesis 1.3 by using the particle distribution generated from the beam dynamics simulation. The results show that for a single stage HGHG, 33.6 nm wavelength FEL radiation can be seeded at FLASH2 with a 235 nm seeding laser.

MOP086	Broadly Tunable THz FEL Amplifier	FEL, laser, electron, radiation	252
	C.H. Chen, F.H. Chao, Y.C. Chiu, Y.K. Gan, K.Y. Huang, Y.-C. Huang, Y.C. Wang NTHU, Hsinchu, Taiwan
	Funding: MOST 102-2112-M-007 -002 -MY3, Taiwan In this paper we present a broadly tunable sub-MW THz FEL amplifier driven by a photoinjector with a sub-kW seed THz source tunable between 0.7-2.0 THz. Specifically an S-band photoinjector at 2.856 GHz generate a 3.3-5.5 MeV electron bunch with 0.5 nC charge in a 4.25 ps rms bunch length, which is injected into a 2-m long undulator with a period of 18 mm and an rms undulator parameter of 0.98. The driver laser of the photoinjector is a frequency quadrupled amplified, mode-locked Nd:YVO4 laser at 1064 nm. We recycle the unconverted infrared laser at 1064 nm to pump a THz parametric amplifier using a lithium niobate crystal as its gain crystal. This THz parametric amplifier generates a transform-limited THz pulse with sub-kW power between 0.7 and 2.0 THz, which is seeded into the undulator to produce broadly tunable, transform-limited, sub-MW THz radiation through FEL amplification with a gain of about 3000. Since the pump laser of the THz OPA is derived from the driver laser of the photoinjector, the seed THz pulse is fully synchronized and overlapped with the electron bunch. Experimental progress of this work will be presented in the conference. *Work supported by MoST under NSC 102-2112-M-007-002-MY3
	Poster MOP086 [1.269 MB]

MOP087	Upgrade Plans for the Short-pulse Facility at DELTA	laser, electron, radiation, dipole	255
	S. Hilbrich, H. Huck, M. Huck, M. Höner, S. Khan, C. Mai, A. Meyer auf der Heide, R. Molo, H. Rast, P. Ungelenk DELTA, Dortmund, Germany
	Funding: Work supported by DFG, BMBF, FZ Jülich, and by the Land NRW. DELTA is a 1.5-GeV synchrotron light source operated by the TU Dortmund University with a short-pulse facility based on Coherent Harmonic Generation (CHG) * to produce radiation with wavelengths in the VUV regime. Even shorter wavelengths can be generated by an upgrade based on the Echo-Enabled Harmonic Generation (EEHG) technique ** which requires additional magnetic chicanes and undulators. A new storage ring lattice provides enough free space for an EEHG setup and additionally for a femtoslicing undulator. Besides the new optics, first simulation results of EEHG will be presented. * S. Khan et al., Sync. Rad. News 26, 3 (2013). ** G. Stupakov, Phys. Rev. Lett. 102, 074801 (2009).

MOP090	Soft X-ray Self-seeding Simulation Methods and their Application for LCLS	radiation, simulation, FEL, optics	264
	S. Serkez DESY, Hamburg, Germany Y. Ding, Z. Huang, J. Krzywinski SLAC, Menlo Park, California, USA
	Self-seeding is a promising approach to significantly narrow the SASE bandwidth of XFELs to produce nearly transform-limited pulses. We study radiation propagation through the grating monochromator installed at LCLS. The monochromator design is based on a toroidal variable line spacing grating working at a fixed incidence angle mounting without an entrance slit. It covers the spectral range from 500eV to 1000eV. The optical system was studied using wave optics method to evaluate the performance of the self-seeding scheme. Our wave optics analysis takes into account the finite size of the coherent source, third-order aberrations and height error of the optical elements. Wave optics is the only method available, in combination with FEL simulations, to simulate performance of the monochromator without exit slit. Two approaches for time-dependent simulations are presented, compared and discussed. Also pulse-front tilt phenomenon effect is illustrated.

MOP094	Indirect Measurements of NIR and UV Ultrashort Seed Laser Pulses using a Transverse Deflecting RF-Structure	laser, electron, experiment, interaction-region	272
	N. Ekanayake, S. Ackermann DESY, Hamburg, Germany S. Ackermann, C. Lechner, Th. Maltezopoulos, T. Plath Uni HH, Hamburg, Germany K.E. Hacker DELTA, Dortmund, Germany
	Seeding of free-electron lasers (FELs) using external coherent optical pulses recently became an area of interest as users demand spectrally and temporally coherent FEL radiation which is not achievable in traditional self-amplified spontaneous emission operation mode. Since temporal and spectral properties of the seed laser pulses are directly imprinted on the electron bunch, a proper characterization of these seed pulses is needed. However, the lack of any measurement technique capable of characterizing ultrashort seed laser pulses at the laser-electron interaction region is a primary drawback. In this paper we report indirect measurements of seed laser pulses in an undulator section using a transverse deflecting RF-structure (TDS-LOLA) at the free-electron laser FLASH at DESY. Temporally chirped and unchirped seed pulse length measurements will be compared with second-harmonic generation frequency-resolved optical gating measurements and theoretical simulations. Using this technique we will demonstrate that pulse artifacts such as pre- and post-pulses in the seed pulse in the femtosecond and picosecond timescales can be identified without any temporal ambiguity. Authors acknowledge the support received from FLASH team and many groups at DESY in preparation and commissioning of experiments. We thank our colleagues in the FLASH seeding team for their support.

MOP096	Enhancing the Harmonic Content of an HGHG Microbunch	electron, laser, simulation, bunching	281
	K.E. Hacker DELTA, Dortmund, Germany
	Funding: BMBF grant 05K10PE1 and DESY High Gain Harmonic Generation (HGHG) seeding has been demonstrated in the visible and ultraviolet, but it is limited in performance at high harmonics of the seed by the initial uncorrelated energy spread of the electron beam. A recent proposal from SINAP using a chirped electron beam and a canted pole undulator has suggested a new mechanism for cooling the uncorrelated energy spread of the electron beam in order to improve the performance of HGHG seeding at high harmonics. This note reviews the mechanism, the limitation of the concept and extrapolates to some new concepts using analogous mechanisms derived from transverse gradients of the laser properties. The impact of CSR wakes on the vanishingly short microbunches produced by the methods are also investigated. [1] H. Deng and C. Feng, Phys. Rev. Lett. 111, 084801 (2013)

MOP097	A Concept for Seeding 4-40 nm FEL Radiation at FLASH2	electron, laser, FEL, bunching	286
	K.E. Hacker DELTA, Dortmund, Germany
	Funding: Work supported by BMBF (contract 05K13PE3) This note describes a scheme to seed the FLASH2 FEL over a range of 4-40 nm without impacting SASE capabilities. This scheme combines multiple seeding techniques, builds on current infrastructure and offers a maximized range of performance with higher pulse energies than what are available at lower-peak current facilities. The concept relies on Echo Enabled Harmonic Generation (EEHG), cascaded seeding, and Second Harmonic Afterburners (SHAB) while maintaining the possibility to operate with High Gain Harmonic Generation (HGHG) seeding at >30 nm wavelengths.

MOC01	Circular Polarization Control by Reverse Undulator Tapering	FEL, resonance, bunching, electron	297
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	In order to produce circularly polarized light at X-ray FEL facilities one can consider an installation of a short helical (or cross-planar) afterburner, but then one should have an efficient method to suppress powerful linearly polarized background from the main undulator. We propose a new method for such a suppression: an application of the reverse taper in the main undulator. We discover that in a certain range of the taper strength, the density modulation (bunching) at saturation is practically the same as in the case of non-tapered undulator while the power of linearly polarized radiation is suppressed by orders of magnitude. Then strongly modulated electron beam radiates at full power in the afterburner. Considering SASE3 undulator of the European XFEL as a practical example, we demonstrate that soft X-ray radiation pulses with peak power in excess of 100 GW and an ultimately high degree of circular polarization can be produced. The method can be used at different X-ray FEL facilities, in particular at LCLS after installation of the helical afterburner in the near future.
	Slides MOC01 [1.545 MB]

MOC03	Radiation Properties of Tapered Hard X-ray Free Electron Lasers	radiation, electron, FEL, simulation	300
	C. Emma, C. Pellegrini UCLA, Los Angeles, USA S.D. Chen NCTU, Hsinchu, Taiwan K. Fang, C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA S. Serkez DESY, Hamburg, Germany
	We perform an analysis of the transverse coherence of the radiation from a TW level tapered hard X-ray Free Electron Laser (FEL). The radiation properties of the FEL are studied for a Gaussian, parabolic and uniform transverse electron beam density profile in a 200-m undulator at a resonant wavelength of 1.5 Angstrom. Simulations performed using the 3-D FEL particle code GENESIS show that diffraction of the radiation occurs due to a reduction in optical guiding in the tapered section of the undulator. This results in an increasing transverse coherence for all three transverse electron beam profiles. We determine that for each case considered the radiation coherence area is much larger than the electron beam spot size, making X-ray diffraction experiments possible for TW X-ray FELs.
	Slides MOC03 [3.797 MB]

MOC04	Chirped and Modulated Electron Pulse Free Electron Laser Techniques	electron, radiation, FEL, simulation	303
	J. Henderson, L.T. Campbell, B.W.J. MᶜNeil USTRAT/SUPA, Glasgow, United Kingdom
	Funding: We acknowledge STFC MoA 4132361; ARCHIE-WeSt HPC, EPSRC grant EP/K000586/1; John von Neumann Institute for Computing (NIC) on JUROPA at Jlich Supercomputing Centre (JSC), under project HHH20 A potential method to improve the free electron laser's output when the electron pulse has a large energy spread is investigate and results presented. A simplified model is the first given, in which there are a number of linearly chirped beamlets equally separated in energy and time. By using chicanes, radiation from one chirped beamlet is passed to the next, helping to negate the effect of the beamlet chirps and maintaining resonant interactions. Hence the addition of chicane allow the electrons to interact with a smaller range of frequencies (Δ ω <2 ρ γ_r), sustaining the FEL interaction. One method to generate such a beamlet structure is presented and is shown to increase FEL performance by two orders of magnitude.
	Slides MOC04 [6.777 MB]

TUB01	Review of Coherent SASE Schemes	electron, FEL, bunching, experiment	327
	B.W.J. MᶜNeil, L.T. Campbell, J. Henderson USTRAT/SUPA, Glasgow, United Kingdom D.J. Dunning, N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Funding: We acknowledge STFC Agreement No. 4163192; ARCHIE-WeSt HPC, EPSRC grant EP/K000586/1; John von Neumann Institute for Computing (NIC) on JUROPA at Julich Supercomputing Centre (JSC), project HHH20 A review is presented of some of the methods and their origins that have recently been proposed to improve the temporal coherence of SASE output. These methods do not require any external laser seed field, or the use of the so-called self-seeding methods, where the SASE radiation is optically filtered and improved at an early stage of the interaction before re-injection and amplification to saturation. By using methods that introduce an additional relative propagation between the electron beam and the radiation field, the localised collective interaction, which leads to the formation of the ‘spiking’ associated with normal SASE output, is removed. The result is output pulses which are close to the fourier transform limit without the need for any external seeds or intermediate optics.
	Slides TUB01 [6.256 MB]

TUP006	Two-color Free-electron Laser via Two Orthogonal Undulators	FEL, polarization, electron, radiation	358
	N.S. Mirian IPM, Tehran, Iran G. Dattoli ENEA C.R. Frascati, Frascati (Roma), Italy V. Petrillo Universita' degli Studi di Milano, Milano, Italy
	An amplifier Free electron Laser (FEL) including two orthogonal polarized undulators with different periods and field intensities is able to emit two color radiations with different frequency and polarization while the total length of device does not change respect to usual single color FELs. The wavelengths of two different colors can be changed by choosing different periods, while variation in the magnetic strengths can be used to modify the gain lengths.

TUP007	Spectral Limits and Frequency Sum-rule of Current and Radiation Noise Measurement	electron, radiation, distributed, FEL	362
	A. Gover, R. Ianconescu University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel A. Nause UCLA, Los Angeles, USA
	Funding: This research was supported by a grant from the United States-Israel Binational Science Foundation(BSF), Jerusalem, ISRAEL The current noise spectrum of an electron beam is generally considered white and expressed by the shot-noise formula (eI0). It is possible to control the spectral energy of a random electron beam current by longitudinal space charge microdynamics and dispersive transport. Both noise suppression (relative to eI0)[1,2] and noise enhancement[3] have been demonstrated, exhibiting sub/super-Poissonian particle distribution statistics, respectively. We present a general theory for the current noise of an e-beam and its radiation emission in the entire spectrum. The measurable current noise spectrum is not white. It is cut-off at high frequencies, limited by the measurement length and the beam axial momentum spread (fundamentally limited by quantum uncertainty). We show that under certain conditions the current noise spectrum satisfies a frequency sum-rule: exhibiting noise enhancement in one part of the spectrum when suppressed at another part and vice versa. The spontaneous emission (radiation noise) into a single radiation mode or single direction in any scheme (OTR, Undulator etc.) is sub-radiant when the beam current is sub-Poissonian and vice versa, but the sum-rule does not apply.

TUP012	Numerical Simulation of a Super-radiant THz Source Driven by Femtosecond Electron Bunches	electron, FEL, radiation, emittance	374
	R.V. Chulkov B.I. Stepanov Institute of Physics, Belarus, Russia V.A. Goryashko Uppsala University, Uppsala, Sweden V. Zhaunerchyk University of Gothenburg, Gothenburg, Sweden
	Funding: We would like to acknowledge the financial support from the Swedish FEL center. Pulsed THz FELs are typically driven by rf Linacs which produce intense electron bunches with a duration of a few picoseconds or even shorter. When the bunch duration is less than a picosecond, the wavelength of the THz light is greater than the bunch length and the FEL operates in the super-radiant (SR) regime. In the report, we summarize our studies performed for an SR source operating in the THz frequency range. In particular, we focus on an open-type planar undulator comprising no guiding structure. Using a numerical code that supports 3D modeling of the SR dynamics as well as statistical properties of electron bunches, we analyze influence of electron bunch parameters on generated THz radiation and reveal some surprising results. More specifically, for the considered undulator configuration, we predict degradation in the angular divergence and spectral broadening of the generated radiation as the electron bunch emittance decreases. We also demonstrate how electron bunch broadening associated with the electron energy spread can eventually be suppressed. R. Chulkov, V. Goryashko, and V. Zhaunerchyk, Report III of the series of reports by the Swedish FEL Center and FREIA Group, http://www.diva-portal.org/smash/get/diva2:699684/FULLTEXT01.pdf.
	Poster TUP012 [1.553 MB]

TUP015	Radiation and Interaction of Layers in Quasi-plane Electron Bunches Moving in Undulators	radiation, electron, laser, free-electron-laser	388
	N. Balal Ariel University, Ariel, Israel V.L. Bratman IAP/RAS, Nizhny Novgorod, Russia
	The model of radiating planes (1D radiating gas) consisting of electrons that oscillate and travel with a relativistic translational velocity allows one to develop a simple general theory describing a number of important effects of radiation in a undulator for dense electron bunches formed in photoinjector accelerators. Having based on this method and taking into account both Coulomb and radiation interactions of the planes with an arbitrary density, particle velocity distribution and energy chirp we have found analytically and numerically efficiency and frequency spectrum for coherent spontaneous radiation, including conditions for generation of minimum narrow and very broadband spectra. The developed theory has been applied for estimation of a powerful terahertz radiation source with a moderate energy of electrons.

TUP017	Using Lorentz Transformations for Simulations of Wiggler Superradiance from the Picosecond Electron Bunches	electron, simulation, radiation, scattering	395
	A. Malkin, N.S. Ginzburg, A.A. Golovanov, I.V. Zotova IAP/RAS, Nizhny Novgorod, Russia V.P. Tarakanov LPI, Moscow, Russia
	Funding: This work was supported by Russian Foundation for Basic Research under Grant No 12-02-01152. In this paper we present a theoretical analysis of superradiance (SR) from picosecond electron bunches wiggling in periodical undulator field based both on the method of averaged ponderomotive force and on a direct numerical PIC (particle-in-cell) simulation. Within both approaches the analysis takes place in the reference frame co-moving with electrons which allows simplifying the procedure of simulation significantly due to the fact that all the spatial scales including the radiation wavelength, the length of the beam and the length of the pump field pacet into which the undulator field is transformed are of the same order. We show that in the reference frame the SR effect can be interpreted as a formation of the distributed Bragg mirror in the bulk of the electron beam which is effectively reflecting (scattering) the pump wave. A possibility of generation of multimegawatt pulses in terahertz and far infrared wave ranges is demonstrated.

TUP018	Sensitivity Study of a Tapered Free-Electron Laser	FEL, electron, emittance, free-electron-laser	399
	A.W.L. Mak, F. Curbis, S. Werin MAX-lab, Lund, Sweden
	The output power of a free-electron laser (FEL) can be greatly enhanced by tapering the undulator line. In this work, a sensitivity study of a tapered FEL is presented. The study is conducted using the numerical simulation code GENESIS and a taper optimization method. Starting from a possible case for the future X-ray FEL at the MAX IV Laboratory in Lund, Sweden, a number of parameters are varied systematically and the impact on the FEL power is investigated. These parameters include the electron beam's initial energy, current, emittance, energy spread, as well as the seed radiation power.

TUP019	Update on the FEL Code Genesis 1.3	electron, radiation, lattice, FEL	403
	S. Reiche PSI, Villigen PSI, Switzerland
	The widely used time-dependent code Genesis 1.3 has been modified to address new needs of users worldwide. The existing limitation of tracking isolated slices of the FEL beam has been overcome by keeping the entire electron beam in memory, which is tracked as a whole through the undulator. This modification allows for additional features such as allowing particles to migrate into other slices or applying self-consistent wakefield and space charge models.

TUP020	MINERVA, a New Code to Model Free-Electron Lasers	FEL, electron, experiment, simulation	408
	H. Freund, P.J.M. van der Slot CSU, Fort Collins, Colorado, USA P.J.M. van der Slot Mesa+, Enschede, The Netherlands
	Simulation codes modelling the interaction of electrons with an optical field inside an undulator are an essential tool for understanding and designing free-electron lasers (FELs). As there exists a large variety of FELs ranging from long-wavelength oscillators using partial wave guiding to soft and hard x-ray FELs that are either seeded or starting from noise, a simulation code should be capable of modelling this huge variety of FEL configurations. A new code under development, named MINERVA, will be capable of modelling such a large variety of FELs. The code uses a modal expansion for the optical field, e.g., a Gaussian expansion for free-space propagation, and an expansion in waveguide modes for propagation at long wavelengths, or a combination of the two for partial guiding at THz frequencies. MINERVA uses the full Newton-Lorentz force equation to track the particles through the optical and magnetic fields. To allow propagation of the optical field outside the undulator and interact with optical elements, MINERVA interfaces with the optical propagation code OPC to model oscillators. Here we describe the main features of MINERVA and give various examples of its capabilities.

TUP021	Recent Updates to the Optical Propagation Code OPC	diagnostics, FEL, electron, free-electron-laser	412
	P.J.M. van der Slot, K.J. Boller Mesa+, Enschede, The Netherlands P.J.M. van der Slot CSU, Fort Collins, Colorado, USA
	Funding: This research is supported in part by Office of Naval Research Global, grant number N62909-10-1-7151 In order to understand and design free-electron lasers (FELs), simulation codes modeling the interaction of electrons with a co-propagating optical field in the magnetic field of an undulator are essential. However, propagation of the optical field outside the undulator is equally important for evaluation of the optical field at the location of the application or to model FEL oscillators. The optical propagation code OPC provides such capabilities and can interface with FEL gain codes like GENESIS 1.3, MEDUSA and MINERVA. Here we present recent additions and modifications to the code that (i) improves the speed of the code and (ii) extends the modeling capabilities. These include amongst other, inline diagnostics that results in considerable faster runtimes, the ability to convert from free-space modes to guided modes (currently only cylindrical waveguides), and the possibility to determine the spectrum at each transverse location. The latter opens the possibility to include dispersion in the optical propagation. Finally, work is underway to support HDF5 to remain compatible with the upcoming new release of GENESIS 1.3.

TUP022	The Implementation of 3D Undulator Fields in the Unaveraged FEL Simulation Code Puffin	electron, FEL, focusing, simulation	416
	J. Henderson, L.T. Campbell, B.W.J. MᶜNeil USTRAT/SUPA, Glasgow, United Kingdom A.R. Maier CFEL, Hamburg, Germany A.R. Maier Uni HH, Hamburg, Germany
	Funding: We acknowledge STFC MoA 4132361; ARCHIE-WeSt HPC, EPSRC grant EP/K000586/1; John von Neumann Institute for Computing (NIC) on JUROPA at Jlich Supercomputing Centre (JSC), under project HHH20 The FEL simulation code Puffin is modified to include 3D magnetic undulator fields. Puffin, having previously used a 1D undulator field, is modified to accommodate general 3D magnetic fields. Both plane and curved pole undulators have been implemented. The electron motion for both agrees with analytic predictions.

TUP025	TW X-ray Free Electron Laser Optimisation by Transverse Pulse Shaping	electron, FEL, radiation, simulation	425
	C. Emma, C. Pellegrini UCLA, Los Angeles, USA C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA
	We study the dependence of the peak power of a 1.5 Angstrom TW, tapered X-ray free-electron laser on the transverse electron density distribution. Multidimensional optimization schemes for TW hard X-Ray free electron lasers are applied to the cases of transversely uniform and parabolic electron beam distributions and compared to a Gaussian distribution. The optimizations are performed for a 200 m undulator and a resonant wavelength of 1.5 Angstrom using the fully 3-dimensional FEL particle code GENESIS. The study shows that the flatter transverse electron distributions enhance optical guiding in the tapered section of the undulator and increase the maximum radiation power from a maximum of 1.56 TW for a transversely Gaussian beam to 2.26 TW for the parabolic case and 2.63 TW for the uniform case. Spectral data also shows a 30-70 % reduction in energy deposited in the sidebands for the uniform and parabolic beams compared with a Gaussian.

TUP026	Transverse Coherence Properties of a TGU-based FEL	FEL, electron, radiation, emittance	429
	P. Baxevanis, Z. Huang, R.D. Ruth SLAC, Menlo Park, California, USA C.B. Schroeder LBNL, Berkeley, California, USA
	The use of a transverse gradient undulator (TGU) is considered an attractive option for FELs driven by electron beams with a relatively large energy spread. In this scheme, a dispersion is introduced in the beam while the undulator poles are inclined so that the undulator field acquires a linear dependence upon the transverse position in the direction of dispersion. By suitably selecting the dispersion and the field gradient, the energy spread effect can be significantly mitigated, thus avoiding a drastic reduction in the FEL gain. However, adding the dispersion typically leads to electron beams with large aspect ratios. As a result, the presence of higher-order modes in the output FEL radiation can become significant. To investigate this effect, we study the properties of the higher-order eigenmodes of a TGU-based, high-gain FEL, using both a simplified, analytically-solvable model and a variational technique. This formalism is then used to provide an estimate of the degree of transverse coherence for a representative soft X-ray, TGU FEL example.

TUP027	Initial Value Problem for an FEL Driven by an Asymmetric Electron Beam	FEL, electron, radiation, simulation	433
	P. Baxevanis, R.D. Ruth SLAC, Menlo Park, California, USA
	FEL configurations in which the driving electron beam is not axially symmetric (round) are important in the study of novel concepts (such as TGU-based FELs) but also become relevant when one wishes to explore the degree to which the deviation from symmetry-inevitable in practical cases-affects the performance of more conventional FEL schemes. In this paper, we present a technique for solving the initial value problem of such an asymmetric FEL. Extending an earlier treatment of ours, we start from a self-consistent, fully 3D, evolution equation for the complex amplitude of the electric field of the FEL radiation, which is then solved by expanding the radiation amplitude in terms of a set of orthogonal transverse modes. The numerical results from such an analysis are in good agreement with simulation and provide a full description of the radiation in the linear regime. Moreover, when the electron beam sizes are constant, this approach can be used to verify the predictions of the standard eigenmode formalism.

TUP028	Mode Contents Analysis of a Tapered Free Electron Laser	FEL, electron, laser, simulation	437
	S.D. Chen, K. Fang, X. Huang, C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA S.D. Chen, C.-S. Hwang NCTU, Hsinchu, Taiwan C. Emma, C. Pellegrini UCLA, Los Angeles, USA K. Fang, S.-Y. Lee Indiana University, Bloomington, Indiana, USA C.-S. Hwang NSRRC, Hsinchu, Taiwan S. Serkez DESY, Hamburg, Germany
	For the ultimate use for the scientific experiments, the free electron laser (FEL) will propagate for long distance, much longer than the Rayleigh range, after exiting the undu- lator. To characterize the FEL for this purpose, we study the electromagnetic field mode components of the FEL photon beam. With the mode decomposition, the transverse coher- ence can be analyzed all along. The FEL here in this paper is a highly tapered one evolving through the exponential growth and then the post-saturation taper. Modes contents are analyzed for electron bunch with three different types of transverse distribution: flattop, Gaussian, and parabolic. The tapered FEL simulation is performed with Genesis code. The FEL photon beam transverse electric field is decom- posed with Gaussian-Laguerre polynomials. The evolutions of spot size, source location, and the portion of the power in the fundamental mode are discussed here. The approach can be applicable to various kind scheme of FEL.

TUP029	iSASE Study	electron, FEL, radiation, simulation	442
	K. Fang Indiana University, Bloomington, Indiana, USA S.D. Chen NCTU, Hsinchu, Taiwan S.D. Chen, K. Fang, X. Huang, C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA C. Emma, C. Pellegrini UCLA, Los Angeles, USA S. Reiche PSI, Villigen PSI, Switzerland
	Improved Self Amplified Spontaneous Emission (iSASE) is a scheme that reduces FEL bandwidth by increasing phase slippage between the electron bunch and radiation field. This is achieved by repeatedly delaying electrons using phase shifters between undulator sections. Genesis code is modified to facilitate this simulation. With this simulation code, the iSASE bandwidth reduction mechanism is studied in detail. A Temporal correlation function is introduced to describe the similarity between the new grown field from bunching factor and the amplified shifted field. This correlation function indicates the efficiency of iSASE process.

TUP030	Mode Component Evolution and Coherence Analysis in Terawatt Tapered FEL	FEL, electron, radiation, laser	446
	K. Fang, S.D. Chen, X. Huang, C. Pellegrini, J. Wu SLAC, Menlo Park, California, USA S.D. Chen NCTU, Hsinchu, Taiwan C. Emma, C. Pellegrini UCLA, Los Angeles, USA K. Fang Indiana University, Bloomington, Indiana, USA C.-S. Hwang NSRRC, Hsinchu, Taiwan S. Serkez DESY, Hamburg, Germany
	A fast and robust algorithm is developed to decompose FEL radiation field transverse distribution into a set of orthonormal basis. Laguerre Gaussian and Hermite Gaussian can be used in the analysis. The information of mode components strength and Gaussian beam parameters allows users in downstream better utilize FEL. With this method, physics of mode components evolution from starting stage, to linear regime and post saturation are studied with detail. With these decomposed modes, correlation function can be computed with less complexity. Eigenmodes of the FEL system can be solved using this method.

TUP031	FEL Code Comparison for the Production of Harmonics via Harmonic Lasing	FEL, electron, simulation, radiation	451
	G. Marcus, W.M. Fawley SLAC, Menlo Park, California, USA S. Reiche PSI, Villigen PSI, Switzerland E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	Harmonic lasing offers an attractive option to significantly extend the photon energy range of FEL beamlines. Here, the fundamental FEL radiation is suppressed by various combinations of phase shifters, attenuators, and detuned undulators while the radiation at a desired harmonic is allowed to grow linearly. The support of numerical simulations is extensively used in evaluating the performance of this scheme. This paper compares the results of harmonic growth in the harmonic lasing scheme using three FEL codes: FAST, GENESIS, and GINGER.

TUP032	FEL Simulation and Performance Studies for LCLS-II	electron, FEL, simulation, radiation	456
	G. Marcus, Y. Ding, P. Emma, Z. Huang, T.O. Raubenheimer, L. Wang, J. Wu SLAC, Menlo Park, California, USA
	The design and performance of the LCLS-II free-electron laser beamlines are presented using start-to-end numerical particle simulations. The particular beamline geometries were chosen to cover a large photon energy tuning range with x-ray pulse length and bandwidth flexibility. Results for self-amplified spontaneous emission and self-seeded operational modes are described in detail for both hard and soft x-ray beamlines in the baseline design.

TUP033	Broadly Tunable Free-Electron Laser for Four-wave Mixing Experiments with Soft X-ray Pulses	electron, FEL, laser, simulation	461
	G. Marcus SLAC, Menlo Park, California, USA G. Penn LBNL, Berkeley, California, USA A. Zholents ANL, Argonne, Illinois, USA
	This paper examines a FEL design for the production of three soft x-ray pulses from a single electron beam suitable for four-wave mixing experiments. Independent control of the wavelength, timing and angle of incidence of the three ultra-short, ultra-intense pulses with exquisite synchronization is critical. A process of selective amplification where a chirped electron beam and a tapered undulator are used to isolate the gain region to only a short fraction of the electron beam is explored in detail. Numerical particle simulations are used to demonstrate the essential features of this scheme in the context of the LCLS-II design study.

TUP035	Investigation of Reverse Taper to Optimize the Degree of Polarization for the Delta Undulator at the LCLS	radiation, polarization, simulation, bunching	465
	J.P. MacArthur Stanford University, Stanford, California, USA Z. Huang, A. Lutmann, A. Marinelli, T.J. Maxwell, H.-D. Nuhn, D.F. Ratner SLAC, Menlo Park, California, USA
	Funding: U.S. Department of Energy under contract No. DE-AC02-76SF00515 A 3.2 m adjustable phase Delta undulator* will soon be installed on the last girder of the LCLS undulator line. The Delta undulator will act as an afterburner terminating the 33 undulator line, providing arbitrary polarization control to users. Two important figures of merit for users will be the degree of polarization and the x-ray yield. In anticipation of this installation, machine development time at the LCLS was devoted to maximizing the final undulator x-ray contrast and yield with a standard canted pole undulator acting as a stand in for the Delta undulator. Following the recent suggestion** that a reverse taper (dK/dz > 0) in the main undulator line could suppress linearly polarized light generated before an afterburner while still producing the requisite microbunching, we report on a reverse taper study at the LCLS wherein a yield contrast of 15 was measured along the afterburner. We also present 1D simulations comparing the reverse taper technique to other schemes. * Nuhn, H.-D., Anderson, S., Bowden, G., Ding, Y., Gassner, G., et al., (2013). ** Schneidmiller, E. A. and Yurkov, M. V., Phys. Rev. ST Accel. Beams 16, 110702 (2013).

TUP040	Flying RF Undulator	electron, radiation, resonance, focusing	474
	A.V. Savilov, I.V. Bandurkin, S.V. Kuzikov, A.A. Vikharev IAP/RAS, Nizhny Novgorod, Russia
	A new concept for the room-temperature rf undulator, designed to produce coherent X-ray radiation by means of a relatively low-energy electron beam and pulsed mm-wavelength radiation, is proposed. The “flying” undulator is a high-power short rf pulse co-propagating together with a relativistic electron bunch in a helically corrugated waveguide. The electrons wiggle in the rf field of the -1st spatial harmonic with the phase velocity directed in the opposite direction in respect to the bunch velocity, so that particles can irradiate high-frequency Compton’s photons. A high group velocity (close to the speed of light) ensures long cooperative motion of the particles and the co-propagating rf pulse. This work is supported by the Russian Foundation for Basic Research (Projects 14-08-00803 and 14-02-00691).
	Poster TUP040 [0.189 MB]

TUP042	High Efficiency Lasing with a Strongly Tapered Undulator	laser, electron, radiation, experiment	478
	J.P. Duris, P. Musumeci UCLA, Los Angeles, California, USA
	Funding: This work was supported by DOE grant DE-FG02-92ER40693, Defense of Threat Reduction Agency award HDTRA1-10-1-0073 and University of California Office of the President award 09-LR-04-117055-MUSP. Typical electrical to optical energy conversion efficiencies for FELs are limited by the Pierce parameter to 10^-3 or smaller. Undulator tapering schemes have enabled extraction of as much as 1 or 2% of the electron energy. Recently, the UCLA BNL helical inverse free electron laser (IFEL) experiment at ATF demonstrated energy doubling and acceleration of 30% of an electron beam from 52 to 93 MeV with a modest 10¹¹ W power CO2 laser pulse. By reversing and retuning the undulator, the electrons may be violently decelerated, thereby transferring energy from the beam to the laser pulse. Simulations show that by sending a 1 kA, 70 MeV electron beam and 100 GW laser into a prebuncher and the reversed undulator, 41% of the electron beam energy should be converted to radiation, allowing the laser pulse power to grow to 127 GW.

TUP045	IFEL Driven Micro-Electro-Mechanical System Free Electron Laser	electron, FEL, laser, radiation	481
	N.S. Sudar, J.P. Duris, P. Musumeci UCLA, Los Angeles, USA
	The Free Electron Laser has provided modern science with a tunable source of high frequency, high power, coherent radiation. To date, short wavelength FEL's have required large amounts of space in order to achieve the necessary beam energy to drive the FEL process and to reach saturation of the output radiation power. By utilizing new methods for beam acceleration as well as new undulator technology, we can decrease the space required to build these machines. In this paper, we investigate a scheme by which a tabletop XUV FEL might be realized. Utilizing the Rubicon Inverse Free Electron Laser (IFEL) at BNL together with micro-electro-mechanical system (MEMS) undulator technology being developed at UCLA, we propose a design for a compact XUV FEL.

TUP046	Terahertz FEL based on Photoinjector Beam in RF Undulator	focusing, electron, FEL, radiation	485
	S.V. Kuzikov, I.V. Bandurkin, M.E. Plotkin, A.V. Savilov, A.A. Vikharev IAP/RAS, Nizhny Novgorod, Russia A.V. Savilov NNGU, Nizhny Novgorod, Russia
	Photoinjectors, which can produce picosecond electron bunches of MeV-level, are attractive for THz generation. Fortunately, a long distance to reach scattering power saturation in FEL is not necessary, if bunch length is shorter than the produced THz half-wavelength. However, the energy of several MeVs does not allow providing long traveling of the flying bunch without longitudinal divergence. That is why, we suggest using specific RF undulator in a form of the normal wave in the helical waveguide at 3 cm wavelength. The mentioned wave has the -1st space harmonic with transverse fields and negative phase velocity (responsible for particle wiggling). This wave has also the 0th harmonic with longitudinal field and positive phase velocity equal to bunch velocity. Due to the synchronous 0th harmonic one can channel low-energy bunches (due to longitudinal focusing field) as far as several meters distance. One might also inject electron bunches in slightly accelerating field, in this case the output THz pulse obtain nearly linear frequency modulation. Such long THz pulses with the mentioned modulation of the frequency can be effectively compressed by pair of diffraction gratings.
	Poster TUP046 [2.914 MB]

TUP047	Chirped Pulse Superradiant Free-electron Laser	radiation, electron, laser, FEL	489
	Y.-C. Huang, C.H. Chen NTHU, Hsinchu, Taiwan J. Wu, Z. Zhang SLAC, Menlo Park, California, USA
	Funding: This work is supported by Ministry of Science and Technology under Contract NSC 102-2112-M-007-002-MY3 When a short electron bunch traverses an undulator and radiates a wavelength significantly longer than the bunch length, the electrons quickly loses energy through so-called superradiance and generate a negatively chirped radiation frequency at the output. In this paper, we develop a theory to describe this chirped-pulse radiation and numerically demonstrate pulse compression by using a quadratic phase filter. As a design example at THz, a photoinjector/linac system generates a 15 MeV electron bunch containing 15-pC charge in a 60-fs duration. The electrons radiate a chirped pulse at 2.5 THz from a 1.5 m long undulator with a period of 5.6 cm and undulator parameter of 1.7. By using a grating pair, the output THz field can be compressed from 27 to 3 cycles. As another example at EUV, a future dielectric laser accelerator [1] is assumed to generate a 100 MeV electron bunch containing 75-fC charge in 1-nm long length. The electrons radiate a chirped EUV pulse at 13.5 nm from a 15.8 cm long dielectric laser undulator [2] with a period of 1.05 mm and undulator field of 3.3 T. By using a quadratic phase filter as a pulse compressor, the peak power of the EUV radiation is increased from 0.7 to 10 kW. Y.C. Huang and R.L. Byer, Appl. Phys. Lett. 69 (15), (1996) 2185-2177. *T. Plettner, R. L. Byer., Phys. Rev. ST Accel. Beams 11, (2008) 030704.

TUP049	Storage Ring XFEL with Longitudinal Focusing	FEL, storage-ring, insertion, optics	492
	I.V. Agapov, G. Geloni XFEL. EU, Hamburg, Germany
	In present work we investigate the possibility of running a high gain FEL on a storage ring using a longitudinally focusing insertion to compress bunches passing an undulator. If integrated into a storage ring similar to PETRA III such device could potentially produce continuous ∼1ps pulses of photons in the nm range with peak pulse powers of tens of GW. Even without operating in FEL saturation mode the longitudinal focusing can provide means to increase the brightness and shorten the photon pulse length

TUP057	Development of Compact THz-FEL System at Kyoto University	gun, electron, FEL, simulation	501
	S. Suphakul, T. Kii, H. Ohgaki, Y. Tsugamura, H. Zen Kyoto University, Kyoto, Japan Q.K. Jia USTC/NSRL, Hefei, Anhui, People's Republic of China
	We are developing a compact accelerator based terahertz (THz) radiation source by free-electron laser (FEL) at the Institute of Advanced Energy, Kyoto University. The system consists of a 1.6 cell BNL type photocathode RF-gun, a focusing solenoid magnet, a magnetic bunch compressor, focusing quadrupoles and an undulator. The system generates an ultra-short electron pulse in a few hundred femtoseconds shorter than radiation wavelength, resulting in super-radiant emission from the undulator. The target radiation wavelength is 100 to 300 μm. A tracking simulation and optimization are performed by using PARMELA and General Particle Tracer (GPT) code. The FEL radiations are analyzed by a 1 dimensional FEL theory. The design parameters, simulation results and status are reported and discussed in this paper.

TUP066	Facility for Coherent THz and FIR Radiation	bunching, FEL, radiation, electron	512
	A. Meseck HZB, Berlin, Germany V.G. Ziemann Uppsala University, Uppsala, Sweden
	Linac based THz sources are increasingly becoming the method of choice for a variety of research fields, justifying the increasing demand for high repetition rate THz FEL facilities world wide. In particular, pump and probe experiments with THz and IR radiation are of major interest for the user community. In this paper, we propose a facility which accommodates an SRF-linac driven cw THz-FEL in combination with an IR undulator which utilizes the microbunched beam. The layout permits almost perfect synchronization between pump and probe pulse as well as nearly independently tunable THz and IR radiation.
	Poster TUP066 [1.655 MB]

TUP082	Coherent Harmonic Generation at the DELTA Storage Ring: Towards User Operation	electron, laser, radiation, experiment	556
	A. Meyer auf der Heide, S. Hilbrich, H. Huck, M. Huck, M. Höner, S. Khan, C. Mai, R. Molo, H. Rast, A. Schick, P. Ungelenk DELTA, Dortmund, Germany
	Funding: Work supported by DFG, BMBF, FZ Jülich, and by the Land NRW. At DELTA, a 1.5-GeV synchrotron light source at the TU Dortmund University, a short-pulse facility based on Coherent Harmonic Generation (CHG) is in operation and shall soon be used for pump-probe experiments. Due to the interaction of ultrashort laser pulses with electron bunches in an undulator, CHG provides short and coherent pulses at harmonics of the laser wavelength. In this paper, recent progress towards user operation, pulse characterization studies such as transverse and longitudinal coherence measurements as well as CHG in the presence of an RF phase modulation are presented.

TUP083	ALPHA – The THz Radiation Source based on AREAL	radiation, electron, FEL, emittance	561
	T.L. Vardanyan, G.A. Amatuni, V.S. Avagyan, A. Grigoryan, B. Grigoryan, M. Ivanyan, V.G. Khachatryan, V.H. Petrosyan, V. Sahakyan, A. Sargsyan, A.V. Tsakanian, V.M. Tsakanov, A. Vardanyan, G.S. Zanyan CANDLE SRI, Yerevan, Armenia
	Advanced Research Electron Accelerator Laboratory (AREAL) based on photo cathode RF gun is under construction at the CANDLE. The basic aim of this new facility is to generate sub-picosecond duration electron bunches with an extremely small beam emittance and energies up to 50 MeV. One of the promising directions of the facility development is the creation of ALPHA (Amplified Light Pulse for High-end Applications) experimental stations with coherent radiation source in THz region based on the concept of both conventional undulator and novel radiation sources. The status of the AREAL facility, the main features and outlooks for the ALPHA station are presented in this work.

TUP086	Experiment Preparation Towards a Demonstration of Laser Plasma Based Free Electron Laser Amplification	electron, laser, FEL, free-electron-laser	569
	M.-E. Couprie, C. Benabderrahmane, P. Berteaud, C. Bourassin-Bouchet, F. Bouvet, F. Briquez, L. Cassinari, L. Chapuis, M.E. El Ajjouri, C. Herbeaux, N. Hubert, M. Labat, A. Lestrade, A. Loulergue, J. Lüning, O. Marcouillé, J.L. Marlats, F. Marteau, C. Miron, P. Morin, F. Polack, K. Tavakoli, M. Valléau, D. Zerbib SOLEIL, Gif-sur-Yvette, France I.A. Andriyash, G. Lambert, V. Malka, C. Thaury LOA, Palaiseau, France S. Bielawski, C. Evain, C. Szwaj PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France X. Davoine CEA/DAM/DIF, Arpajon, France
	One direction towards compact Free Electron Laser is to replace the conventional linac by a laser plasma driven beam, provided proper electron beam manipulation to handle the value of the energy spread and of the divergence. Applying seeding techniques also enables to reduce the required undulator length. Rapidly developing Laser Wakefield Accelerators (LWFA) are already able to generate synchrotron radiation. With the presently achieved electron divergence and energy spread an adequate beam manipulation through the transport to the undulator is needed for FEL amplification. A test experiment for the demonstration of FEL amplification with a LWFA is under preparation in the frame of the COXINEL ERC contract in the more general context of LUNEX5. Electron beam transport follows different steps with strong focusing thanks to variable strength permanent magnet quadrupoles, demixing chicane with conventional dipoles, and a second set of quadrupoles for further focusing in the undulator. Progress on the equipment preparation and expected performance are described.

TUP087	The Status of LUNEX5 Project	electron, FEL, laser, operation	574
	M.-E. Couprie, C. Benabderrahmane, P. Berteaud, C. Bourassin-Bouchet, F. Bouvet, F. Briquez, L. Cassinari, L. Chapuis, J. Daillant, M. Diop, M.E. El Ajjouri, C. Herbeaux, N. Hubert, M. Labat, P. Lebasque, A. Lestrade, A. Loulergue, P. Marchand, O. Marcouillé, J.L. Marlats, C. Miron, P. Morin, A. Nadji, F. Polack, F. Ribeiro, J.P. Ricaud, P. Roy, K. Tavakoli, M. Valléau, D. Zerbib SOLEIL, Gif-sur-Yvette, France S. Bielawski PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France B. Carré, D. Garzella CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France X. Davoine CEA/DAM/DIF, Arpajon, France N. Delerue LAL, Orsay, France G. Devanz, A. Mosnier CEA/DSM/IRFU, France A. Dubois, J. Lüning CCPMR, Paris, France C. Evain, E. Roussel, C. Szwaj PhLAM/CERLA, Villeneuve d'Ascq, France G. Lambert, R. Lehé, V. Malka, A. Rousse, C. Thaury LOA, Palaiseau, France C. Madec CEA/IRFU, Gif-sur-Yvette, France
	LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short, intense, coherent Free Electron Laser (FEL) pulses in the 40-4 nm spectral range. It comprises a 400 MeV superconducting Linear Accelerator for high repetition rate operation (10 kHz), multi-FEL lines and adapted for studies of advanced FEL schemes, a 0.4 - 1 GeV Laser Wake Field Accelerator (LWFA) for its qualification by a FEL application, a single undulator line enabling seeding with High order Harmonic in Gas and echo configurations and pilot user applications. Concerning the superconducting linac, the electron beam dynamics has been modified from a scheme using a third harmonic linearizer and a compression chicane to dog-leg coupled to sextupoles. Besides, the choice of the gun is under revision for fulfilling to 10 kHz repetition rate. Following transport theoretical studies of longitudinal and transverse manipulation of a LWFA electron beam enabling to provide theoretical amplification, a test experiment is under preparation in collaboration with the Laboratoire d’Optique Appliquée towards an experimental demonstration.

TUP088	Free Electron Lasers in 2014	FEL, electron, laser, free-electron-laser	580
	J. Blau, K. R. Cohn, W.B. Colson, W.W. Tomlinson NPS, Monterey, California, USA
	Funding: This work has been supported by the Office of Naval Research and the High Energy Laser Joint Technology Office. Thirty-eight years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are tabulated and discussed.

TUP089	The Turkish Accelerator and Radiation Laboratory in Ankara (TARLA) Project	electron, FEL, radiation, linac	585
	A.A. Aksoy, Ö. Karslı, C. Kaya, O. Yavaş Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey P. Arıkan Gazi University, Faculty of Arts and Sciences, Teknikokullar, Ankara, Turkey S. Özkorucuklu Istanbul University, Istanbul, Turkey
	Funding: Work is supported by Ministry of Development of Turkey with Grand No: DPT2006K-120470 The Turkish Accelerator and Radiation Laboratory in Ankara (TARLA) which is proposed as a first facility of Turkish Accelerator Center (TAC) Project will operate two Infra-Red Free Electron Lasers (IR-FEL) covering the range of 3-250 microns. The facility will consist of an injector fed by a thermionic triode gun with two-stage RF bunch compression, two superconducting accelerating modules operating at continuous wave (CW) mode and two independent optical resonator systems with different undulator period lengths. The electron beam will also be used to generate Bremsstrahlung radiation. The facility aims to be first user laboratory in the region of Turkey in which both electromagnetic radiation and particles will be used. In this paper, we discuss design goals of the project and present status and road map of the project.

TUP095	Design of a Compact Light Source Accelerator Facility at IUAC, Delhi	electron, gun, radiation, laser	596
	S. Ghosh, R.K. Bhandari, G.K. Chaudhari, D. Kanjilal, J. Karmakar, N. Kumar, A. Pandey, P. Patra, A. Rai, B.K. Sahu IUAC, New Delhi, India A.S. Aryshev, J. Urakawa KEK, Ibaraki, Japan A. Deshpande, T.S. Dixit SAMEER, Mumbai, India V. Naik, A. Roy VECC, Kolkata, India
	Funding: * The project is supported jointly by Board of Research in Nuclear Sciences and Inter University Accelerator Center The demand for a light source with high brightness and short pulse length from the researchers in the field of physical, chemical, biological and medical sciences is growing in India. To cater to the experimental needs of multidisciplinary sciences, a project to develop a compact Light Source at Inter University Accelerator Centre (IUAC) has been taken up. In the first phase of the project, prebunched [1] electron beam of ~ 8 MeV will be produced by a photocathode RF gun and coherent THz radiation will be produced by a short undulator magnet. In the second phase, the energy of the electron beam will be increased up to 50 MeV by two sets of superconducting niobium resonators. The coherent IR radiation will be produced by using an undulator magnet (conventional method) and X-rays by Inverse Compton Scattering. To increase the average brightness of the electromagnetic radiation, fabrication of superconducting RF gun is going to be started in a parallel development. In this paper the detailed design of the LSI accelerator complex as well as construction timetable will be presented. The physical principles of THz generation and major accelerator subsystems will be discussed. [1] S. Liu & J.Urakawa, Proc. of FEL 2011, page-92

TUC01	Hard X-ray Self-Seeding Setup and Results at SACLA	electron, FEL, radiation, photon	603
	T. Inagaki, N. Adumi, T. Hara, T. Ishikawa, R. Kinjo, H. Maesaka, Y. Otake, H. Tanaka, T. Tanaka, K. Togawa, M. Yabashi RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan S. Goto, Y. Inubushi, T.K. Kameshima, T. Ohata, K. Tono JASRI/SPring-8, Hyogo, Japan T. Hasegawa, S. Tanaka SES, Hyogo-pref., Japan H. Kimura, A. Miura, H. Ohashi, H. Yamazaki Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), Hyogo, Japan
	In order to improve the spectral and temporal properties of XFEL, the self-seeding option based on the transmission crystal optics has been implemented in SACLA since 2012. The self-seeding setup composed of four dipole magnets that can generate up to 50 fs temporal delay and a diamond single crystal with the thickness of 180 micro-m has been installed at the position of the 9th undulator segment, which has been moved downstream. In 2013, the installation of all the components has been completed in August and the commissioning has been started in October. After a number of tuning processes such as the beam collimation and undulator K-value optimization, significant spectral narrowing has been confirmed at 10 keV with the C(400) Bragg reflection. The spectral bandwidth of seeded FEL is about 3 eV, which is nearly one order narrower than that of SASE measured without the diamond crystal. The peak spectral intensity of seeded FEL is about 5 times higher than that of SASE. Systematic optimization on beam properties is now in progress towards experimental use of seeded XFELs. This talk gives the overview of the plan, achieved results and ongoing R&D.
	Slides TUC01 [20.337 MB]

WEB03	European XFEL Construction Status	photon, electron, laser, diagnostics	623
	W. Decking DESY, Hamburg, Germany F. Le Pimpec XFEL. EU, Hamburg, Germany
	The European XFEL is presently constructed in the Hamburg region, Germany. It aims at producing X-rays in the range from 260 eV up to 24 keV out of three undulators that can be operated simultaneously with up to 27000 pulses/second. The FEL is driven by a 17.5 GeV linear accelerator based on TESLA-type superconducting accelerator modules. This paper presents the status of major components, the present project schedule and a summary of beam parameters that are adapted to the evolving needs of the users.
	Slides WEB03 [12.982 MB]

WEB04	The New IR FEL Facility at the Fritz-Haber-Institut in Berlin	FEL, electron, cavity, radiation	629
	W. Schöllkopf, W. Erlebach, S. Gewinner, H. Junkes, A. Liedke, G. Meijer, A. Paarmann, G. von Helden FHI, Berlin, Germany H. Bluem, D. Dowell, R. Lange, J. Rathke, A.M.M. Todd, L.M. Young AES, Princeton, New Jersey, USA S.C. Gottschalk STI, Washington, USA U. Lehnert, P. Michel, W. Seidel, R. Wünsch HZDR, Dresden, Germany
	A mid-infrared oscillator FEL has been commissioned at the Fritz-Haber-Institut. The accelerator consists of a thermionic gridded gun, a subharmonic buncher and two S-band standing-wave copper structures [1,2]. It provides a final electron energy adjustable from 15 to 50 MeV, low longitudinal (<50 keV-ps) and transverse emittance (<20 π mm-mrad), at more than 200 pC bunch charge with a micro-pulse repetition rate of 1 GHz and a macro-pulse length of up to 15 μs. Regular user operation started in Nov. 2013 with 6 user stations. Pulsed radiation with up to 100 mJ macro-pulse energy at about 0.5% FWHM bandwidth is routinely produced in the wavelength range from 4 to 48 μm. We will describe the FEL design and its performance as determined by IR power, bandwidth, and micro-pulse length measurements. Further, an overview of the new FHI FEL facility and first user results will be given. The latter include, for instance, spectroscopy of bio-molecules (peptides and small proteins) conformer selected or embedded in superfluid helium nano-droplets at 0.4 K, as well as vibrational spectroscopy of mass-selected metal-oxide clusters and protonated water clusters in the gas phase. [1] W. Schöllkopf et al., MOOB01, Proc. FEL 2012. [2] W. Schöllkopf et al., WEPSO62, Proc. FEL 2013.
	Slides WEB04 [12.785 MB]

WEB05	FLASH: First Soft X-ray FEL Operating Two Undulator Beamlines Simultaneously	electron, operation, laser, photon	635
	K. Honkavaara, B. Faatz, J. Feldhaus, S. Schreiber, R. Treusch, M. Vogt DESY, Hamburg, Germany
	FLASH, the free electron laser user facility at DESY (Hamburg, Germany), has been upgraded with a second undulator beamline FLASH2. After a shutdown to connect FLASH2 to the FLASH linac, FLASH1 is back in user operation since February 2014. Installation of the FLASH2 electron beamline has been completed early 2014, and the first electron beam was transported into the new beamline in March 2014. The commissioning of FLASH2 takes place in 2014 parallel to FLASH1 user operation. This paper reports the status of the FLASH facility, and the first experience of operating two FEL beamlines.
	Slides WEB05 [2.481 MB]

THA02	Experimental Characterization of FEL Polarization Control with Cross Polarized Undulators	polarization, FEL, radiation, controls	644
	E. Ferrari, E. Allaria, G. De Ninno, B. Diviacco, D. Gauthier, L. Giannessi, G. Penco, C. Spezzani Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy J. Buck, M. Ilchen XFEL. EU, Hamburg, Germany G. De Ninno, D. Gauthier University of Nova Gorica, Nova Gorica, Slovenia L. Giannessi ENEA C.R. Frascati, Frascati (Roma), Italy Z. Huang, A.A. Lutman SLAC, Menlo Park, California, USA G. Lambert, B. Mahieu LOA, Palaiseau, France J. Viefhaus DESY, Hamburg, Germany
	Polarization control of the coherent radiation is becoming an important feature of recent and future short wavelength free electron laser facilities. While polarization tuning can be achieved taking advantage of specially designed undulators, a scheme based on two consecutive undulators emitting orthogonally polarized fields has also been proposed. Developed initially in synchrotron radiation sources, crossed polarized undulator schemes could benefit from the coherent emission that characterize FELs. In this work we report the first detailed experimental characterization of the polarization properties of an FEL operated with crossed polarized undulators in the Soft-X-Rays. Aspects concerning the average degree of polarization and the shot to shot stability are investigated together with a comparison of the performance of various schemes to control and switch the polarization
	Slides THA02 [5.383 MB]

THA03	A Plan for the Development of Superconducting Undulator Prototypes for LCLS-II and Future FELs	FEL, linac, vacuum, electron	649
	P. Emma, N.R. Holtkamp, H.-D. Nuhn SLAC, Menlo Park, California, USA D. Arbelaez, J.N. Corlett, S.A. Myers, S. Prestemon, D. Schlueter LBNL, Berkeley, California, USA C.L. Doose, J.D. Fuerst, E. Gluskin, Q.B. Hasse, Y. Ivanyushenkov, M. Kasa, G. Pile, E. Trakhtenberg ANL, Argonne, Ilinois, USA
	Funding: Work supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515, DE-AC02-05CH11231, and DE-AC02-06CH11357. Undulators serve as the primary source of radiation for modern storage rings, and more recently for the advent of Free-Electron Lasers (FELs). The performance of future FELs can be greatly enhanced using the much higher magnetic fields of superconducting undulators (SCU). For example, the LCLS-II hard x-ray undulator can be shortened by up to 70 m using an SCU in place of a PMU (permanent magnet undulator), or its spectral performance can be critically improved when using a similar length. In addition, SCUs are expected to be orders of magnitude less sensitive to radiation dose; a major issue at LCLS-II with its 1-MHz electron bunch rate. We present a funded R&D collaboration between SLAC, ANL, and LBNL, which aims to demonstrate the viability of superconducting undulators for FELs by building, testing, measuring, and tuning two 1.5-m long planar SCU prototypes using two different technologies: NbTi at ANL and Nb3Sn at LBNL. Our goal is to review and reassess the LCLS-II HXR baseline plans (PMU) in July of 2015, after the development and evaluation of both prototypes, possibly in favor of an SCU for LCLS-II.
	Slides THA03 [29.468 MB]

THB04	Electron Beam Diagnostics and Feedback for the LCLS-II	cavity, feedback, diagnostics, controls	666
	J.C. Frisch, P. Emma, A.S. Fisher, P. Krejcik, H. Loos, T.J. Maxwell, T.O. Raubenheimer, S.R. Smith SLAC, Menlo Park, California, USA
	Funding: work supported by DOE contract DE-AC02-76-SF00515 The LCLS_II is a CW superconducting accelerator driven, hard and soft X-ray Free Electron Laser which is planned to be constructed at SLAC. It will operate with a variety of beam modes from single shot to approximately 1 MHz CW at bunch charges from 10pc to 300pC with average beam powers up to 1.2 MW. A variety of types of beam instrumentation will be used, including stripline and cavity BPMS, fluorescent and OTR based beam profile monitors, fast wire scanners and transverse deflection cavities. The beam diagnostics system is designed to allow tuning and continuous measurement of beam parameters, and to provide signals for fast beam feedbacks.
	Slides THB04 [1.501 MB]

THP014	Cyclotron-Undulator Cooling of a Free-Electron-Laser Beam	electron, radiation, cyclotron, FEL	710
	A.V. Savilov, I.V. Bandurkin, S.V. Kuzikov IAP/RAS, Nizhny Novgorod, Russia
	We propose methods of fast cooling of an electron beam, based on wiggling of particles in an undulator in presence of an axial magnetic field. We use a strong dependence of the axial electron velocity on the oscillatory velocity, when the electron cyclotron frequency is close to the frequency of electron wiggling in the undulator field. Such cooling may open a way for creating a compact X-ray free-electron laser based on the stimulated scattering of a powerful laser pulse on a moderately-relativistic (several MeV) electron beam. This work is supported by the Russian Foundation for Basic Research (Projects 14-08-00803 and 14-02-00691).
	Poster THP014 [0.166 MB]

THP018	The Seed Laser System for the Proposed VUV FEL Facility at NSRRC	laser, FEL, electron, radiation	718
	M.C. Chou, N.Y. Huang, W.K. Lau, A.P. Lee NSRRC, Hsinchu, Taiwan
	The possibility of establishing a free electron laser facility in Taiwan has been a continuing effort at NSRRC in the past several years. The baseline design of the envisioned NSRRC FEL is a high gain harmonic generation (HGHG) FEL seeded by a 266 nm laser. The seed laser is produced by adding an optical parametric amplification (OPA) system pumped by upgrading the existing IR laser system. To provide broad tunability of the FEL radiation, the seed laser will be tunable. The spectrum considered for seeding the FEL is between 266 - 800 nm with peak power of 200 MW. The spatial and temporal overlap between the sub-100 fs electron bunch and the 100 fs UV seed laser is under study.
	Poster THP018 [0.152 MB]

THP025	Linear Accelerator Design for the LCLS-II FEL Facility	linac, electron, FEL, laser	743
	P. Emma, J.C. Frisch, Z. Huang, H. Loos, A. Marinelli, T.J. Maxwell, Y. Nosochkov, T.O. Raubenheimer, L. Wang, J.J. Welch, M. Woodley SLAC, Menlo Park, California, USA J. Qiang, M. Venturini LBNL, Berkeley, California, USA A. Saini, N. Solyak Fermilab, Batavia, Illinois, USA
	Funding: Work supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515. The LCLS-II is an FEL facility proposed in response to the July 2013 BESAC advisory committee, which recommended the construction of a new FEL light source with a high-repetition rate and a broad photon energy range from 0.2 keV to at least 5 keV. A new CW 4-GeV electron linac is being designed to meet this need, using a superconducting (SC) L-band (1.3 GHz) linear accelerator capable of operating with a continuous bunch repetition rate up to 1 MHz at ~16 MV/m. This new 700-m linac is to be built at SLAC in the existing tunnel, making use of existing facilities and providing two separate FELs, preserving the operation of the existing FEL, which can be fed from either the existing copper or the new SC linac. We briefly describe the acceleration, bunch compression, beam transport, beam switching, and electron beam diagnostics. The high-power and low-level RF, and cryogenic systems are described elsewhere.
	Poster THP025 [0.627 MB]

THP029	MOGA OPTIMIZATION DESIGN OF LCLS-II LINAC CONFIGURATIONS	linac, emittance, FEL, simulation	763
	L. Wang, P. Emma, Y. Nosochkov, T.O. Raubenheimer, M. Woodley, F. Zhou SLAC, Menlo Park, California, USA C. F. Papadopoulos, J. Qiang, M. Venturini LBNL, Berkeley, California, USA
	The Linac Coherent Light Source II (LCLS-II) will generate extremely intense X-ray flashes to be used by researchers from all over the world. The FEL is powered by 4 GeV superconducting linear accelerator, operating with a 1 MHz bunch repetition rate. LCLS-II will provide large flexibility in bunch charge and peak current. Multi-Objective Genetic Algorithm (MOGA) is applied to optimize the machine parameters including bunch compressors system, linearizer, de-chirper, RF phase and laser heater, in order to minimize the energy spread, collective effects and emittance. The strong resistive wall wake field along the 2km bypass beam line acts as a natural de-chirper. This paper summarizes the optimization of various configurations.
	Poster THP029 [0.702 MB]

THP059	The Laser Heater System of SwissFEL	laser, electron, emittance, operation	871
	M. Pedrozzi, M. Calvi, R. Ischebeck, S. Reiche, C. Vicario PSI, Villigen PSI, Switzerland B.D. Fell, N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Short wavelength FELs are generally driven by high-brilliance photo-cathode RF-guns which generate electron beams with an uncorrelated energy spread on the order of 1 keV or less. These extremely cold beams can easily develop micro-bunching instabilities caused by longitudinal space charge forces after the compression process. This can result in a blow up of the energy spread and emittance beyond the tolerable level for SASE emission. It has been demonstrated theoretically and experimentally [1] that a controlled increase of the uncorrelated energy spread to typically a few keV is sufficient to strongly reduce the instability growth. In the laser heater system, one achieves a controlled increase of the beam energy spread by a resonant interaction of the electron beam with a transversally polarized laser beam inside of an undulator magnet. The momentum modulation resulting from the energy exchange within the undulator is consequently smeared out in the transmission line downstream of the laser heater system. In SwissFEL, the laser heater system is located after the first two S-band accelerating structures at a beam energy of 150 MeV. This paper describes the layout and the sub-components of this system. [1] Z. Huang, et al, Phys. Rev. Special Topics – Accelerator and beams 13, 020703 (2010)

THP073	Optics Measurements at FLASH2	optics, extraction, linac, emittance	902
	M. Scholz, B. Faatz, M. Vogt, J. Zemella DESY, Hamburg, Germany
	FLASH2 is a newly build second beam line at FLASH, the soft X-ray FEL at DESY, Hamburg. Unlike the existing beam line FLASH1, it is equipped with variable gap undulators. This beam line is currently being commissioned. Both undulator beam lines of FLASH are driven by a common linear accelerator. Fast kickers and a septum are installed at the end of the linac to distribute the electron bunches of every train between FLASH1 and FLASH2. A specific beam optic in the extraction arc with horizontal beam waists in the bending magnets is mandatory in order to mitigate CSR effects. Here we will show first results of measurements and compare to simulations.

THP087	Electron Beam Diagnostics for COXINEL	electron, diagnostics, plasma, FEL	937
	M. Labat, C. Bourassin-Bouchet, L. Cassinari, M.-E. Couprie, M.E. El Ajjouri, N. Hubert, A. Loulergue SOLEIL, Gif-sur-Yvette, France
	On the path towards more compact free electron lasers (FELs), the project COXINEL was recently funded: a transfer line will be installed to adapt a plasma accelerated beam (from LOA) into an in-vacuum undulator built by SOLEIL. This experiment should enable to demonstrate the first FEL based on a plasma accelerator. Because plasma beams are intrinsically very different from RF acceletor beams (much shorter, divergent and smaller with a higher energy spread and energy jitter), their transport and matching in the undulator is critical if willing to obtain a significant amplification. This is why special care has to be taken in the design of the beam diagnostics to be able to measure the transverse beam sizes, energy spread and jitter, emittance and bunch length. For these purposes, several diagnostics will be implemented from the plasma accelerator exit down to the undulator exit. In each station, several screen types will be available and associated to high resolution imaging screens. In this paper, we present the experimental layout and associated simulation of the diagnostics performances.

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MOA03

First Lasing at FLASH2

electron, operation, photon, laser

7

S. Schreiber, B. Faatz
DESY, Hamburg, Germany

FLASH, the free-electron laser user facility at DESY (Hamburg, Germany), has been upgraded with a second undulator beamline FLASH2. The installation of the FLASH2 electron beamline, including twelve variable gap undulators, was finalized early 2014, and beam commissioning of the new beamline started in March 2014. We announce first lasing at FLASH2 achieved at a wavelength of 40 nm on August 20, 2014.

Slides MOA03 [3.896 MB]

MOB01

Pulse Control in a Free Electron Laser Amplifier

FEL, electron, radiation, laser

9

L. Giannessi
ENEA C.R. Frascati, Frascati (Roma), Italy

Funding: Work supported by MIUR (DM1834 RIC.4-12-2002 and Grants No. FIRB- RBAP045JF2 and No. FIRB-RBAP06AWK3), and by the EU Commission in the Sixth Framework Program, Contract No. 011935- EUROFEL.
A significant progress has been made in controlling the properties of the radiation emitted by a FEL amplifier. Experiments have demonstrated the possibility both to increase the temporal coherence and to reduce the amplifier length to reach saturation, by seeding it with an external source. This may be a solid state, short pulse, laser (Ti:Sa,OPA..), doubled or tripled in a crystal, or a high order harmonic pulse generated in gas. The coherence improvement and the increased compactness of the source are only the first beneficial offspring of this marriage between the optical laser world and that of FELs. Non-linear effects in the seeded FEL dynamics may be exploited to shorten the pulse length beyond that allowed by the FEL natural gain bandwidth. Multiple seed pulses can be used to generate pulses whose temporal distance and properties are also controlled. Similarly, the FEL gain can be adapted to match the seed properties by tailoring the electrons phase space to generate ultra-short output pulses at unparalleled intensities. I had the honor (and luck) to participate in many relevant experiments at the SPARC and FERMI FELs and I will give my personal overview.

Slides MOB01 [29.932 MB]

MOP003

Helical Undulator Radiation in Internally Coated Metallic Pipe

radiation, vacuum, synchrotron-radiation, impedance

26

T.L. Vardanyan, A. Grigoryan, L.V. Hovakimyan, M. Ivanyan, A.V. Tsakanian, V.M. Tsakanov
CANDLE SRI, Yerevan, Armenia

The vacuum chambers of many advanced undulator sources are coated internally in order to reduce the impedance of the vacuum chamber or improve the vacuum performance. Although the impedances and radiation properties of the internally coated metallic pipes for straightforward moving charge are well studied, the peculiarities of the particles wiggling motion on the radiation characteristics in such structure are missed. In this paper we obtain exact expressions for the fields of a particle moving along a spiral path, as in the single-layer resistive as well as in the two-layer metallic waveguides, modelling NEG coating of the waveguide walls. Based on these results, it will be possible to obtain the necessary characteristics of the radiation of helical undulators, very close to reality. The solution is obtained as a superposition of a particular solution of inhomogeneous Maxwell's equations in a waveguide with perfectly conducting walls, and the solutions of the homogeneous Maxwell equations in the single-layer and double-layer resistive waveguides. Solution in the form of the multipole expansion for inhomogeneous Maxwell's equations for a waveguide with perfectly conducting walls, are also obtained in this study.

MOP007

High Accuracy Shimming Technique for the Phase Shifters of the European XFEL

operation, simulation, permanent-magnet, electron

29

Y. Li
DESY, Hamburg, Germany
J. Pflüger
XFEL. EU, Hamburg, Germany

For the European XFEL 91 phase shifters are needed, which have to fulfil stringent field integral specifications: There should be no observable beam deflection when the strength, i.e. the magnetic gap is changed In order to facilitate the mass production of 91 phase shifters within the tough XFEL schedule a shimming technique was developed. It is based on measured shim signatures and is straight forward and fast to apply. The method is described and results are presented demonstrating that all requirements can be fulfilled.

MOP008

Temperature Effects of the FLASH2 Undulators

controls, operation, feedback, insertion-device

34

M. Tischer, A. Schöps, P. Vagin
DESY, Hamburg, Germany

FELs are very sensitive to small changes in the resonance condition of the emitted radiation. As a consequence, permanent magnet undulators in FELs usually require extensive temperature control in order to assure stable operation conditions. In principle, the temperature dependence of permanent magnet material is well known but more things need to be considered like different thermal expansion of various mechanical parts or thermally induced deformation which do not only affect the K parameter but also the field quality. We have performed temperature dependent magnetic measurements in a range from 19 to 28 degrees Celsius and have analyzed the magnetic performance of the undulator. The results of this case study can be transferred to all FLASH2 undulators and shall allow for a simple temperature dependent gap correction in order to make the spectral properties insensitive to temperature changes of the insertion devices.

MOP012

Implementation Phase of the European XFEL Photon Diagnostics

photon, diagnostics, FEL, electron

41

J. Grünert, J. Buck, F. Dietrich, W. Freund, A. Koch, M. Planas
XFEL. EU, Hamburg, Germany

The European XFEL facility with 3 undulators and initially 6 experimental end-stations requires an extensive set of photon beam diagnostics for commissioning and user operation, capable of handling the extreme brilliance and its inherent damage potential, and the high intra bunch train repetition rate of 4.5MHz, potentially causing additional damage by high heat loads and making shot-to-shot diagnostics very demanding [1]. After extensive design [2-4] and prototype studies, in 2014 the installation of the photon beam devices starts with the equipment in the first photon tunnel XTD2 which is where the SASE1 hard X-ray undulator is located. This contribution reports on the device construction progress by focusing on the XTD2 tunnel devices and their implementation into the tunnel environment. [1] J.Grünert, Framework for X-Ray Photon Diagnostics at the European XFEL, TR-2012-003, 04/2012 [2] J.Buck, Online Photoemission Time-of-Flight Spectrometer for X-ray Photon Diagnostics, TR-2012-002, 06/2012 [3] C.Ozkan, Conceptual design report for Imaging Stations at the European XFEL, TR-2012-004, 02/2012 [4] W.Freund, The European XFEL Undulator Commissioning Spectrometer, XFEL. EU 05/2011

MOP018

Conceptual Study of a Self-seeding Scheme at FLASH2

FEL, electron, simulation, photon

53

T. Plath, L.L. Lazzarino
Uni HH, Hamburg, Germany
K.E. Hacker
DELTA, Dortmund, Germany

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K1GU4 and 05K10PE1 and the German Research Foundation program graduate school 1355.
We present a conceptual study of a self-seeding installation at the new FEL beamline, FLASH2, at the free-electron laser at DESY, Hamburg. For self-seeding, light from a first set of undulators is filtered by a monochromator and thus acts as a seed for the gain process in the main undulator. This scheme has been tested at LCLS at SLAC with a diamond monochromator for hard X-rays and with a grating monochromator for soft X-rays covering energies between 700 and 1000 eV. For such a design to offer benefits at FLASH2, it must be modified to work with X-rays with wavelength of about 5 nm (248 eV) where the damage threshold of the monochromator in the setup and the divergence at longer wavelengths become an issue. An analysis of the potential performance and limitations of this setup is performed using GENESIS 1.3 and a method developed for the soft X-ray self-seeding experiment at the European XFEL. With a total of 9 undulators in the first stage and 8 undulators after the monochromator, a pulse energy contrast ratio of 4.5 was simulated with an initial peak current of 2.5 kA.

MOP023

Development of a Magnetic System to Cancel the Attractive Force toward Structural Reform of Undulators

multipole, experiment, vacuum, synchrotron

75

R. Kinjo, T. Tanaka
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
A. Kagamihata, T. Seike
JASRI/SPring-8, Sayo-gun, Japan
S. Yamamoto
KEK, Tsukuba, Japan

As part of a development on a compact and lightweight structure toward structural reform of undulators, cancellation of magnetic attractive force is being studied. Undulators usually require rigid mechanical components and frames to control the magnet gap precisely against the large attractive force in between. If the attractive force is canceled out near the point of load, the requirement for the undulator structure is relaxed and the cost and lead time of construction and installation are saved largely. For that purpose, we have proposed to add periodically-magnetized monolithic magnets beside the main magnets, which are expected to generate a repulsive force having the same gap-dependency as the attractive force in a cost-effective way. In the conference, the present status of the development of the force cancellation system will be presented, with a focus on the result of preliminary experiments using the periodically-magnetized magnets. Also introduced will be a development plan for the compact and lightweight undulator based on the cancellation system.

MOP028

Field Integral Measurement System and Optical Alignment System for HUST THz-FEL

FEL, alignment, electron, cavity

80

B. Qin, Q.S. Chen, M. Fan, Q. Fu, T. Hu, X. Lei, K.F. Liu, X. Liu, P. Tan, Y.Q. Xiong, J. Yang, L. Yang
HUST, Wuhan, People's Republic of China
X. Liu, Z. Ouyang, Y.B. Wang
Huazhong University of Science and Technology, State Key Laboratory of Advanced Electromagnetic Engineering and Technology,, Hubei, People's Republic of China
Y.J. Pei
USTC/NSRL, Hefei, Anhui, People's Republic of China

A Free Electron Laser oscillator with radiation wavelength 50–100 μm is under construction in Huazhong University of Science and Technology (HUST). The linear polarization undulator with K=1.0-1.25 has been designed and manufactured by Kyma s.r.l., by using a pure permanent magnet scheme. Acceptance test bas been performed in Kyma factory with well controlled phase error and field integrals for all gaps. This paper introduces the development of an online field integrals measurement system for the undulator, using the stretched wire method. The design and considerations of the optical alignment system is described as well.

MOP030

Performance Analysis of Variable-Period Helical Undulator with Permanent Magnet for a KAERI THz FEL

permanent-magnet, FEL, radiation, simulation

84

J. Mun, K.H. Jang, Y.U. Jeong, K. Lee, S. H. Park, N. Vinokurov
KAERI, Daejon, Republic of Korea
M.Y. Jeon
Chungnam National University, Daejoen, Republic of Korea

Funding: This work was supported by the World Class Institute Program of the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT and Future Planning.(NRF Grant Number:WCI2011-001)
We realized a variable-period permanent-magnet helical undulator with high (~1 T) field amplitude, which is almost constant over undulator periods of 23–26 mm. Each undulator period has 4 modular sections of iron poles and permanent magnets embedded in non-magnetic disks with holes along the undulator axis. Modular plates undergo a longitudinal repulsive force from the magnetic field pressure and the spring coils between modular plates. The undulator period can thus be controlled by mechanically changing of the end plate longitudinal position. This compact design is suitable for a table-top terahertz free electron lasers. The measured on-axis field is about 0.97 T with the deviation less than 1% through the whole range of the undulator period variation. The measured spread of the longitudinal coordinates of the undulator field component maxima is less than 1%, and the measured field distribution meets the requirement for our terahertz FEL. The field reproducibility was checked by six measurements of the undulator field after the period variation for the 26 mm period. The r. m. s. phase errors is 3.7 degrees.

MOP033

Design, Fabrication, and Performance Tests of Dipole and Quadrupole Magnets for PAL-XFEL

quadrupole, dipole, multipole, optics

90

H.S. Suh, M.-H. Cho, S.-H. Jeong, Y.-G. Jung, H.-S. Kang, D.E. Kim, I.S. Ko, H.-G. Lee, S.B. Lee, B.G. Oh, K.-H. Park
PAL, Pohang, Kyungbuk, Republic of Korea

PAL-XFEL is now being constructed in Pohang, Korea. This facility will consist of a 10 GeV linac and five undulator beamlines. As the first phase we will construct one hard X-ray and one soft X-ray beamlines which require 7 different families of dipole magnets, and 11 families of quadrupole magnets. We are designing these magnets with considering the efficient manufacturing and the proper power supplies. In this presentation, we describe the design features of the magnets, the manufacturing, and the thermal analysis with the test results.

MOP036

Estimating Effect of Undulator Field Errors using the Radiation Hodograph Method

radiation, electron, synchrotron-radiation, free-electron-laser

93

N.A. Sokolov
Budker INP & NSU, Novosibirsk, Russia
N. Vinokurov
BINP SB RAS, Novosibirsk, Russia

Spatially-periodic magnetic structures are widely used for generation of high-brilliance radiation in storage rings, sources of synchrotron radiation and free electron lasers. In 1947, V.L. Ginzburg suggested the first undulator scheme. An alternating magnetic field created by a planar undulator makes electrons oscillate in the transverse direction, with interference of radiation emitted from separate parts of the trajectory. The spectrum of the forward emitted radiation is enchanced due to constructive interference. The ondulator is made of the magnetized bars that are not perfect and their magnetization differs. Therefore, the electron trajectory is not purely sinusoidal and, as a result, the spectral intensity fades. The task was to find out if the precision of magnet manufacturing is sufficient. This paper presents modelling of electron motion in the measured magnetic field of the new (third) free electron laser at the Siberian Synchrotron Radiation Centre. We have managed to estimate the effect of the field errors through comparison of the resulting emitted field amplitude with the amplitude from ideal magnet bars using the hodograph method.

MOP037

Modeling and Design of the Variable Period and Pole Number Undulator for the Second Stage of the Novosibirsk FEL

FEL, simulation, permanent-magnet, electron

96

I. Davidyuk
NSU, Novosibirsk, Russia
O.A. Shevchenko, V.G. Tcheskidov, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia
N. Vinokurov
KAERI, Daejon, Republic of Korea

The concept of the permanent magnet variable period undulator (VPU) has been proposed just several years ago and there are few examples of its implementation yet. The VPUs have several advantages compared to conventional undulators. One of them is wider radiation wavelength tunability range and another one is an option to increase the number of poles for shorter periods. Both these advantages will be realized in VPU which is being developed now at Budker INP. In this paper we present the 2-D and 3-D magnetic field simulation results and discuss the design features of this VPU.

MOP038

Characterization of the Undulator Magnetic Field Quality by the Angle Averaged Radiation Spectrum

radiation, electron, photon

100

O.A. Shevchenko, N. Vinokurov
BINP SB RAS, Novosibirsk, Russia
N. Vinokurov
KAERI, Daejon, Republic of Korea

The real undulator magnetic field always contains errors which influence undulator performance. The effect of these errors is usually characterized by broadening of the spontaneous emission spectrum at zero angle and corresponding reduction of the spectral intensity. This approach works very well for the phase errors while it does not take into account transversal trajectory displacements. The integrated over the angles radiation spectrum contains more complete information about the undulator field quality but its calculation requires more effort. Therefore the spectral density of emitted radiation (the total number of emitted photons with given energy) can be considered as a figure of merit for an undulator. In this paper we derive analytical formula for this spectrum suitable for doing efficient numerical calculations and demonstrate its application to the case of some typical undulator field errors.

MOP040

General Strategy for the Commissioning of the ARAMIS Undulators with a 3 GeV Electron Beam

electron, alignment, quadrupole, photon

107

M. Calvi, M. Aiba, M. Brügger, S. Danner, R. Ganter, R. Ischebeck, L. Patthey, T. Schietinger, T. Schmidt
PSI, Villigen PSI, Switzerland

The commissioning of the first SwissFEL undulator line (Aramis) is planned for the beginning of 2017. Each undulator is equipped with a 5-axis camshaft system to remotely adjust its position in the micrometer range and a gap drive system to set K-values between 0.1 and 1.8. In the following paper the beam-based alignment of the undulator with respect to the golden orbit, the definition of look-up tables for the local correction strategy (minimization of undulator field errors), the fine-tuning of the K-values as well as the setting of the phase shifters are addressed. When applicable both electron beam and light based methods are presented and compared.

MOP041

Summary of the U15 Prototype Magnetic Performance

vacuum, electron, quadrupole, photon

111

M. Calvi, M. Aiba, M. Brügger, S. Danner, R. Ganter, C. Ozkan, T. Schmidt
PSI, Villigen PSI, Switzerland

The first undulator prototype (U15) was assembled and magnetically tested. The instrumentation and the algorithms developed for the undulator optimization are presented and a comparison among different approaches is reviewed. The magnetic measurement results before and after the installation of the vacuum components are discussed. The summary of the undulator test with 100 MeV electron beam is presented and the impact of the radiation on the magnetics is addressed.

MOP043

Magnetic Design of an Apple III Undulator for SwissFEL

vacuum, polarization, operation, alignment

116

T. Schmidt, A. Anghel, P. Boehler, M. Brügger, M. Calvi, S. Danner, P. Huber, A. Keller, M. Locher
PSI, Villigen PSI, Switzerland

In the frame of the SwissFEL project a soft x-ray line is planned in the coming years to cover the wavelength between 0.7 and 7.0nm. Based on the good experience at the SLS storage ring with Apple undulator as source of variable polarized light, Apple III type undulators are also foreseen at the SwissFEL. In this paper the design of these devices is introduced and the preliminary magnetic configuration together with the optimization strategy is presented in details.

MOP045

Phase Shifter Design for iSASE

electron, power-supply, FEL, simulation

123

S.D. Chen, K. Fang, H.-D. Nuhn, C. Pellegrini, J. Wu, L. Zhu
SLAC, Menlo Park, California, USA
S.D. Chen, C.-S. Hwang
NCTU, Hsinchu, Taiwan
K. Fang
Indiana University, Bloomington, Indiana, USA
C.-S. Hwang
NSRRC, Hsinchu, Taiwan

A phase shifter to generate an additional phase advance of the spontaneous light versus the electron beam was de- signed for the iSASE scheme. The iSASE mechanism is for reducing the bandwidth further from SASE FEL process. A large phase advance about 1600*2Pi as the FEL operating at wavelength 0.8 nm was needed according to the simulation of iSASE process. Since the iSASE is thought to implement into LCLS II project, the space limitation causing by LCLS II should be considered when designing the phase shifter. An optimized three-pole electric phase shifter with 7.3 mm gap has the center field of 1.8 T . The vanadium steel was considered as pole material and the magnet physical length is 260 mm, meanwhile the water-cooling type copper coil was adopted. The temperature increment, force analysis, low field operation mode concept, and preliminary tolerance study were discussed.

MOP046

Undulator Radiation Damage Experience at LCLS

radiation, electron, operation, experiment

127

H.-D. Nuhn, R.C. Field, Yu.I. Levashov, X.S. Mao, M. Santana-Leitner, J.J. Welch, Z.R. Wolf
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515
The SLAC National Accelerator Laboratory has been running the Linac Coherent Light Source (LCLS), the first x-ray Free Electron Laser since 2009. Undulator magnet damage from radiation, produced by the electron beam traveling through the 133-m long straight vacuum tube, has been and is a concern. A damage measurement experiment has been performed in 2007 in order to obtain dose versus damage calibrations. Radiation reduction and detection devices have been integrated into the LCLS undulator system. The accumulated radiation dose rate was continuously monitored and recorded. In addition, undulator segments have been routinely removed from the beamline to be checked for magnetic (50 ppm, rms) and mechanic (about 0.25 μm, rms) changes. A reduction in strength of the undulator segments is being observed, at a level, which is now clearly above the noise. Recently, potential sources for the observed integrated radiation levels have been investigated. The paper discusses the results of these investigation as well as comparison between observed damage and measured dose accumulations and discusses, briefly, strategies for the new LCLS-II upgrade, which will be operating at more than 300 times larger beam rate.

MOP047

A 200 μm-period Laser-driven Undulator

laser, electron, plasma, alignment

131

F. Toufexis, T. Tang, S.G. Tantawi
SLAC, Menlo Park, California, USA

Funding: This project was funded by U.S. Department of Energy under Contract No. DE-AC02-76SF00515 and the DARPA AXiS program.
To reduce the linac energy required for a given synchrotron radiation wavelength, and hence the size of the device, a smaller undulator period with sufficient field strength is needed. In this work, a microfabricated, laser-driven undulator with 200um undulator period is proposed. A TE wave that co-propagates with the electron beam is excited between two polysilicon thin films, having a gap of 16.5um. The mode that is excited is a deflecting mode and causes the electron beam to wiggle. The device is fabricated on a silicon wafer, using conventional silicon micromachining techniques. A single polysilicon thin film is supported on a silicon chip, which has a slit from the back to allow delivery of the laser beam. Two such chips are bonded together to form a 16.5um gap, within which the electron beam passes through. The final device has dimensions 1cm x 1cm x 1.1mm and has approximately 35 undulator periods. In this paper, the model, design, fabrication, and cold measurements of the device are reported.

MOP052

Update on FEL Performance for SwissFEL

FEL, simulation, radiation, emittance

140

E. Prat, S. Reiche
PSI, Villigen PSI, Switzerland

The SwissFEL project under construction at the Paul Scherrer Institute foresees for 2017 the realization of an X-ray FEL with a photon wavelength down to 1 Å. In this paper we present the expected SASE performance for SwissFEL based on input distributions obtained from detailed start-to-end simulation results. The effects of the longitudinal wakefields due to resistive wall and surface roughness in the undulator beamline have been taken into account. We have studied and optimized the impact on the FEL performance of different factors like the electron focusing or the undulator tapering. Results for the standard cases with 200 pC and 10 pC electron bunch charge are shown.

MOP053

SASE FEL Performance at the SwissFEL Injector Test Facility

FEL, electron, simulation, gun

144

S. Reiche
PSI, Villigen PSI, Switzerland

A 4 m long prototype of the SwissFEL undulator module with an undulator period length of 15 mm was installed at the SwissFEL Injector Test Facility and tested with a 200 MeV electron beam in the beginning of 2014. We observed FEL lasing in SASE mode in the wavelength range from 70 to 800 nm, tuning the wavelength by energy and gap. The measurements of the FEL performance are reported.
on behalf of the SwissFEL Team

MOP054

Harmonic Lasing Options for LCLS-II

electron, photon, radiation, FEL

148

G. Marcus, Y. Ding, Z. Huang, T.O. Raubenheimer
SLAC, Menlo Park, California, USA
G. Penn
LBNL, Berkeley, California, USA

Harmonic lasing can be a cheap and relatively efficient way to extend the photon energy range of a particular FEL beamline. Furthermore, in comparison to nonlinear harmonics, harmonic lasing can provide a beam that is more intense, stable, and narrow-band. This paper explores the application of the harmonic lasing concept at LCLS-II using various combinations of phase shifters and attenuators. In addition, a scheme by which individual undulator modules are tuned to amplify either the third or fifth harmonic in different configurations is presented in detail.

MOP055

Start-to-End Simulations for IR/THz Undulator Radiation at PITZ

electron, radiation, FEL, simulation

153

P. Boonpornprasert, M. Khojoyan, M. Krasilnikov, F. Stephan
DESY Zeuthen, Zeuthen, Germany
B. Marchetti, E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany
S. Rimjaem
Chiang Mai University, Chiang Mai, Thailand

High brightness electron sources for modern linac-based Free-Electron Lasers (FELs) have been characterized and optimized at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). Since the time structure of the electron bunches at PITZ is identical to those at the European XFEL, the PITZ accelerator is being considered as a proper machine for the development of an IR/THz source prototype for pump and probe experiments planned at the European XFEL. Tunable IR/THz radiation sources using synchrotron radiation from a dipole magnet, transition radiation, high gain FELs and coherent radiation of tailored or premodulated beams are currently under consideration. This work describes start-to-end simulations for generating the FEL radiation using an APPLE-II undulator with electron beams produced by the PITZ accelerator. Analysis of the physical parameter space has been performed with tools of the FAST program code package. Electron Beam dynamics simulations were performed by using the ASTRA code, while the GENESIS 1.3 code was used to study the SASE process. The results of these studies are presented and discussed in this paper.

MOP056

SASE Characteristics from Baseline European XFEL Undulators in the Tapering Regime

photon, electron, radiation, FEL

159

I.V. Agapov, G. Geloni
XFEL. EU, Hamburg, Germany
G. Feng, V. Kocharyan, E. Saldin, S. Serkez, I. Zagorodnov
DESY, Hamburg, Germany

The output SASE characteristics of the baseline European XFEL, recently used in the TDRs of scientific instruments and X-ray optics, have been previously optimized assuming uniform undulators without considering the potential of undulator tapering in the SASE regime. Here we demonstrate that the performance of European XFEL sources can be significantly improved without additional hardware. The procedure consists in the optimization of the undulator gap configuration for each X-ray beamline. Here we provide a comprehensive description of the X-ray photon beam properties as a function of wavelength and bunch charge. Based on nominal parameters for the electron beam, we demonstrate that undulator tapering allows one to achieve up to a tenfold increase in peak power and photon spectral density in the conventional SASE regime.

MOP057

Proposal to Generate 10 TW Level Femtosecond X-ray Pulses from a Baseline Undulator in Conventional SASE Regime at the European XFEL

electron, laser, free-electron-laser, FEL

164

E. Saldin, V. Kocharyan, S. Serkez, I. Zagorodnov
DESY, Hamburg, Germany
G. Geloni
XFEL. EU, Hamburg, Germany

Output characteristics of the European XFEL have been previously studied assuming an operation point at 5 kA peak current. Here we explore the possibility to go well beyond such nominal peak current level. We consider a bunch with 0.25 nC charge, compressed up to a peak current of 45 kA. An advantage of operating at such high peak current is the increase of the x-ray output peak power without any modification to the baseline design. Based on start-to-end simulations, we demonstrate that such high peak current, combined with undulator tapering, allows one to achieve up to a 100-fold increase in a peak power in the conventional SASE regime, compared to the nominal mode of operation. In particular, we find that 10 TW-power level, femtosecond x-ray pulses can be generated in the photon energy range between 3 keV and 5 keV, which is optimal for single biomolecule imaging. Our simulations are based on the exploitation of all the 21 cells foreseen for the SASE3 undulator beamline, and indicate that one can achieve diffraction to the desired resolution with 15 mJ (corresponding to about 3·10¹³ photons) in pulses of about 3 fs, in the case of a 100 nm focus at the photon energy of 3.5 keV.

MOP058

Purified SASE Undulator Configuration to Enhance the Performance of the Soft X-ray Beamline at the European XFEL

FEL, electron, radiation, laser

169

V. Kocharyan, E. Saldin, S. Serkez, I. Zagorodnov
DESY, Hamburg, Germany
I.V. Agapov, G. Geloni
XFEL. EU, Hamburg, Germany

The purified SASE (pSASE) undulator configuration recently proposed at SLAC promises an increase in the output spectral density of XFELs. In this article we study a straightforward implementation of this configuration for the soft x-ray beamline at the European XFEL. A few undulator cells, resonant at a subharmonic of the FEL radiation, are used in the middle of the exponential regime to amplify the radiation, while simultaneously reducing the FEL bandwidth. Based on start-to-end simulations, we show that with the proposed configuration the spectral density in the photon energy range between 1.3 keV and 3 keV can be enhanced of an order of magnitude compared to the baseline mode of operation. This option can be implemented into the tunable-gap SASE3 baseline undulator without additional hardware, and it is complementary to the self-seeding option with grating monochromator proposed for the same undulator line, which can cover the photon energy range between about 0.26 keV and 1 keV.

MOP060

Demonstration of SASE Suppression Through a Seeded Microbunching Instability

electron, laser, FEL, free-electron-laser

177

C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach
Uni HH, Hamburg, Germany
S. Ackermann, J. Bödewadt, G. Brenner, M. Dohlus, N. Ekanayake, T. Golz, E. Hass, K. Honkavaara, T. Laarmann, T. Limberg, E. Schneidmiller, N. Stojanovic, M.V. Yurkov
DESY, Hamburg, Germany
K.E. Hacker, S. Khan, R. Molo
DELTA, Dortmund, Germany

Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3 and the German Research Foundation programme graduate school 1355.
Collective effects and instabilities due to longitudinal space charge and coherent synchrotron radiation can degrade the quality of the ultra-relativistic, high-brilliance electron bunches needed for the operation of free-electron lasers. In this contribution, we demonstrate the application of a laser-induced microbunching instability to selectively suppress the SASE process. A significant decrease of photon pulse energies was observed at the free-electron laser FLASH in coincidence with overlap of 800 nm laser pulses and electron bunches within a modulator located approximately 40 meters upstream of the undulators. We discuss the underlying mechanisms based on longitudinal space charge amplification [E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 110701 (2010)] and present measurements.

MOP061

Electron Beam Delays for Improved Temporal Coherence and Short Pulse Generation at SwissFEL

FEL, electron, radiation, simulation

181

N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
S. Reiche
PSI, Villigen PSI, Switzerland

Proposals have been made for the introduction of magnetic electron beam delays in between the undulator modules of a long sectional FEL undulator - these can be used for the generation of trains of FEL pulses which can individually be shorter than the FEL cooperation time [*] or to greatly improve the temporal coherence of the FEL output compared to the nominal SASE configuration [**,***,***]. This paper comprises a feasibility study of the application of these techniques to the SwissFEL hard X-Ray beamline. Three-dimensional simulations are used to investigate the potential photon output.
[*] N.R. Thompson and B.W.J. McNeil, PRL 100:203901, 2008.
[**] N.R. Thompson et al. In Proc IPAC2010, pages 2257–2259, 2010
[***] J. Wu, A. Marinelli, and C. Pellegrini. Proc FEL2012, 2012.

MOP062

FEL Proposal Based on CLIC X-Band Structure

linac, FEL, klystron, linear-collider

186

A.A. Aksoy, O. Yavaş
Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey
E. Adli
University of Oslo, Oslo, Norway
D. Angal-Kalinin, J.A. Clarke
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
M.J. Boland, T.K. Charles, R.T. Dowd, G. LeBlanc
SLSA, Clayton, Australia
N. Charitonidis, A. Grudiev, A. Latina, D. Schulte, I. Syratchev, W. Wuensch
CERN, Geneva, Switzerland
G. D'Auria, S. Di Mitri
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
W. Fang, Q. Gu
SINAP, Shanghai, People's Republic of China
E.N. Gazis
National Technical University of Athens, Athens, Greece
M. Jacewicz, R.J.M.Y. Ruber, V.G. Ziemann
Uppsala University, Uppsala, Sweden
Z. Nergiz
Nigde University, Nigde, Turkey

A linear accelerating structure with an average loaded gradient of 100 MV/m at X-Band frequencies has been demonstrated in the CLIC study. Recently, it has been proposed to use this structure to drive an FEL linac. In contrast to CLIC the linac would be powered by klystrons not by an RF source created by a drive beam. The main advantage of this proposal is achieving the required energies in a very short distance, thus the facility would be rather compact. In this study, we present the structure choice and conceptual design parameters of a facility which could generate laser photon pulses below Angstrom. Shorter wavelengths can also be reached with slightly increasing the energy.

MOP064

Statistical Properties of the Radiation from SASE FEL Operating in a Post-saturation Regime with and without Undulator Tapering

FEL, radiation, free-electron-laser, laser

194

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

We describe statistical and coherence properties of the radiation from x-ray free electron lasers (XFEL) operating in the post-saturation regime. We consider practical case of the SASE3 FEL at European XFEL. We perform comparison of the main characteristics of X-ray FEL operating in the post-saturation regime with and without undulator tapering: efficiency, coherence time and degree of transverse coherence.

MOP065

Optimization of a High Efficiency FEL Amplifier

electron, FEL, radiation, laser

199

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

The problem of an efficiency increase of an FEL amplifier is now of great practical importance. Technique of undulator tapering in the post-saturation regime is used at the existing x-ray FELs LCLS and SACLA, and is planned for use at the European XFEL, Swiss FEL, and PAL XFEL. There are also discussions on the future of high peak and average power FELs for scientific and industrial applications. In this paper we perform detailed analysis of the tapering strategies for high power seeded FEL amplifiers. Application of similarity techniques allows us to derive universal law of the undulator tapering.

MOP066

An Overview of the Radiation Properties of the European XFEL

electron, radiation, operation, hardware

204

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

We present an overview of the radiation properties of the European XFEL based on recently accepted strategy of operation at the fixed set of electron energies (8.5 GeV, 12 GeV, 14 GeV, and 17.5 GeV), baseline parameters if the electron beam, and new set undulator parameters. We also discuss potential extension of the parameter space which does not require new hardware and can be realized at a very early stage of the European XFEL operation.

MOP067

Prospects for CW Operation of the European XFEL in Hard X-ray Regime

electron, linac, operation, FEL

210

R. Brinkmann, E. Schneidmiller, J.K. Sekutowicz, M.V. Yurkov
DESY, Hamburg, Germany

The European XFEL will operate nominally at 17.5 GeV in SP (short pulse) mode with 0.65 ms long bunch train and 10 Hz repetition rate. A possible upgrade of the linac to CW (continuous wave) or LP (long pulse) modes with a corresponding reduction of electron beam energy is under discussion since many years. Recent successes in the dedicated R&D program allow to forecast a technical feasibility of such an upgrade in the foreseeable future. One of the challenges is to provide sub-Angstroem FEL operation in CW and LP modes. In this paper we perform a preliminary analysis of a possible operation of the European XFEL in the hard X-ray regime in CW and LP modes with the energies of 7 GeV and 10 GeV, respectively. We consider lasing in the baseline XFEL undulator as well as in a new undulator with a reduced period. We show that, with reasonable requirements on electron beam quality, lasing on the fundamental will be possible in sub-Angstroem regime. As an option for generation of brilliant photon beams at short wavelengths we also consider harmonic lasing that has recently attracted a significant attention.

MOP068

Suppression of the Fundamental Frequency for a Successful Harmonic Lasing in SASE FELs

FEL, electron, simulation, photon

215

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

Harmonic lasing in X-ray FELs has recently attracted a significant attention and is now seriously considered as a potential method for generation of brilliant photon beams at short wavelengths. It is clear, however, that for a successful harmonic lasing one has to suppress the fundamental. In this paper we discuss different methods for such a suppression: phase shifters, intraundulator spectral filtering, switching between the 3rd and the 5th harmonics etc.

MOP075

Laser Seeding Schemes for Soft X-rays at LCLS-II

laser, electron, bunching, radiation

223

G. Penn
LBNL, Berkeley, California, USA
P. Emma, E. Hemsing, G. Marcus, T.O. Raubenheimer, L. Wang
SLAC, Menlo Park, California, USA

Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract Nos. DE-AC02-05CH11231 and DE-AC02-76SF00515.
The initial design for LCLS-II incorporates both SASE and self-seeded configurations. Increased stability and/or coherence than is possible with either configuration may be provided by seeding with external lasers followed by one or more stages of harmonic generation, especially in the soft x-ray regime. External seeding also allows for increased flexibility, for example the ability to quickly vary the pulse duration. Studies of schemes based on high-gain harmonic generation and echo-enabled harmonic generation are presented, including realistic electron distributions based on tracking through the injector and linac.

MOP079

Generation of Multiple Coherent Pulses in a Superradiant Free-Electron Laser

electron, FEL, radiation, simulation

233

X. Yang, S. Seletskiy
BNL, Upton, Long Island, New York, USA
L. Giannessi
ENEA C.R. Frascati, Frascati (Roma), Italy

We analyze the structure of the tail of a superradiant pulse, which is constituted by a train of sub-pulses with decaying amplitudes. We show how a trailing pulse, with pi phase advance from the leading pulse, is generated at the falling edge of the leading superradiant pulse, where the corresponding phase space is deeply saturated and the electrons become de-trapped by the reduced ponderomotive potential. Once the trailing pulse gains enough energy, it generates a second trailing pulse, and the process takes place again. By performing detailed simulations of the resulting electron phase space distribution and the FEL pulse spectral and temporal structure with PERSEO, we confirm that the deformation and re-bunching of the longitudinal phase space create a sequence of pulses. These results are compared to 3D simulations using the FEL code GENESIS 1.3 showing a good agreement.

MOP083

Start-to-End Simulation for FLASH2 HGHG Option

simulation, radiation, electron, FEL

244

G. Feng, S. Ackermann, J. Bödewadt, W. Decking, M. Dohlus, Y.A. Kot, T. Limberg, M. Scholz, I. Zagorodnov
DESY, Hamburg, Germany
K.E. Hacker
DELTA, Dortmund, Germany
T. Plath
Uni HH, Hamburg, Germany

The Free-electron laser in Hamburg (FLASH) is the first FEL user facility to have produced extreme ultraviolet (XUV) and soft X-ray photons. In order to increase the beam time delivered to users, a major upgrade of FLASH named FLASH II is in progress. The electron beamline of FLASH2 consists of diagnostic and matching sections, a seeding undulator section and a SASE undulator section. In this paper, results from a start-to-end simulation for a FLASH2 High-Gain Harmonic Generation (HGHG) option are presented. For the beam dynamics simulation, space charge, coherent synchrotron radiation (CSR) and longitudinal cavity wake field effects are taken into account. In order to get electron beam bunches with small correlated and uncorrelated energy spread, RF parameters of the accelerating modules have been optimized as well as the parameters of the bunch compressors. Radiation simulations for the modulator and the radiator have been done with code Genesis 1.3 by using the particle distribution generated from the beam dynamics simulation. The results show that for a single stage HGHG, 33.6 nm wavelength FEL radiation can be seeded at FLASH2 with a 235 nm seeding laser.

MOP086

Broadly Tunable THz FEL Amplifier

FEL, laser, electron, radiation

252

C.H. Chen, F.H. Chao, Y.C. Chiu, Y.K. Gan, K.Y. Huang, Y.-C. Huang, Y.C. Wang
NTHU, Hsinchu, Taiwan

Funding: MOST 102-2112-M-007 -002 -MY3, Taiwan
In this paper we present a broadly tunable sub-MW THz FEL amplifier driven by a photoinjector with a sub-kW seed THz source tunable between 0.7-2.0 THz. Specifically an S-band photoinjector at 2.856 GHz generate a 3.3-5.5 MeV electron bunch with 0.5 nC charge in a 4.25 ps rms bunch length, which is injected into a 2-m long undulator with a period of 18 mm and an rms undulator parameter of 0.98. The driver laser of the photoinjector is a frequency quadrupled amplified, mode-locked Nd:YVO4 laser at 1064 nm. We recycle the unconverted infrared laser at 1064 nm to pump a THz parametric amplifier using a lithium niobate crystal as its gain crystal. This THz parametric amplifier generates a transform-limited THz pulse with sub-kW power between 0.7 and 2.0 THz, which is seeded into the undulator to produce broadly tunable, transform-limited, sub-MW THz radiation through FEL amplification with a gain of about 3000. Since the pump laser of the THz OPA is derived from the driver laser of the photoinjector, the seed THz pulse is fully synchronized and overlapped with the electron bunch. Experimental progress of this work will be presented in the conference.
*Work supported by MoST under NSC 102-2112-M-007-002-MY3

Poster MOP086 [1.269 MB]

MOP087

Upgrade Plans for the Short-pulse Facility at DELTA

laser, electron, radiation, dipole

255

S. Hilbrich, H. Huck, M. Huck, M. Höner, S. Khan, C. Mai, A. Meyer auf der Heide, R. Molo, H. Rast, P. Ungelenk
DELTA, Dortmund, Germany

Funding: Work supported by DFG, BMBF, FZ Jülich, and by the Land NRW.
DELTA is a 1.5-GeV synchrotron light source operated by the TU Dortmund University with a short-pulse facility based on Coherent Harmonic Generation (CHG) * to produce radiation with wavelengths in the VUV regime. Even shorter wavelengths can be generated by an upgrade based on the Echo-Enabled Harmonic Generation (EEHG) technique ** which requires additional magnetic chicanes and undulators. A new storage ring lattice provides enough free space for an EEHG setup and additionally for a femtoslicing undulator. Besides the new optics, first simulation results of EEHG will be presented.
* S. Khan et al., Sync. Rad. News 26, 3 (2013).
** G. Stupakov, Phys. Rev. Lett. 102, 074801 (2009).

MOP090

Soft X-ray Self-seeding Simulation Methods and their Application for LCLS

radiation, simulation, FEL, optics

264

S. Serkez
DESY, Hamburg, Germany
Y. Ding, Z. Huang, J. Krzywinski
SLAC, Menlo Park, California, USA

Self-seeding is a promising approach to significantly narrow the SASE bandwidth of XFELs to produce nearly transform-limited pulses. We study radiation propagation through the grating monochromator installed at LCLS. The monochromator design is based on a toroidal variable line spacing grating working at a fixed incidence angle mounting without an entrance slit. It covers the spectral range from 500eV to 1000eV. The optical system was studied using wave optics method to evaluate the performance of the self-seeding scheme. Our wave optics analysis takes into account the finite size of the coherent source, third-order aberrations and height error of the optical elements. Wave optics is the only method available, in combination with FEL simulations, to simulate performance of the monochromator without exit slit. Two approaches for time-dependent simulations are presented, compared and discussed. Also pulse-front tilt phenomenon effect is illustrated.

MOP094

Indirect Measurements of NIR and UV Ultrashort Seed Laser Pulses using a Transverse Deflecting RF-Structure

laser, electron, experiment, interaction-region

272

N. Ekanayake, S. Ackermann
DESY, Hamburg, Germany
S. Ackermann, C. Lechner, Th. Maltezopoulos, T. Plath
Uni HH, Hamburg, Germany
K.E. Hacker
DELTA, Dortmund, Germany

Seeding of free-electron lasers (FELs) using external coherent optical pulses recently became an area of interest as users demand spectrally and temporally coherent FEL radiation which is not achievable in traditional self-amplified spontaneous emission operation mode. Since temporal and spectral properties of the seed laser pulses are directly imprinted on the electron bunch, a proper characterization of these seed pulses is needed. However, the lack of any measurement technique capable of characterizing ultrashort seed laser pulses at the laser-electron interaction region is a primary drawback. In this paper we report indirect measurements of seed laser pulses in an undulator section using a transverse deflecting RF-structure (TDS-LOLA) at the free-electron laser FLASH at DESY. Temporally chirped and unchirped seed pulse length measurements will be compared with second-harmonic generation frequency-resolved optical gating measurements and theoretical simulations. Using this technique we will demonstrate that pulse artifacts such as pre- and post-pulses in the seed pulse in the femtosecond and picosecond timescales can be identified without any temporal ambiguity.
Authors acknowledge the support received from FLASH team and many groups at DESY in preparation and commissioning of experiments. We thank our colleagues in the FLASH seeding team for their support.

MOP096

Enhancing the Harmonic Content of an HGHG Microbunch

electron, laser, simulation, bunching

281

K.E. Hacker
DELTA, Dortmund, Germany

Funding: BMBF grant 05K10PE1 and DESY
High Gain Harmonic Generation (HGHG) seeding has been demonstrated in the visible and ultraviolet, but it is limited in performance at high harmonics of the seed by the initial uncorrelated energy spread of the electron beam. A recent proposal from SINAP using a chirped electron beam and a canted pole undulator has suggested a new mechanism for cooling the uncorrelated energy spread of the electron beam in order to improve the performance of HGHG seeding at high harmonics. This note reviews the mechanism, the limitation of the concept and extrapolates to some new concepts using analogous mechanisms derived from transverse gradients of the laser properties. The impact of CSR wakes on the vanishingly short microbunches produced by the methods are also investigated.
[1] H. Deng and C. Feng, Phys. Rev. Lett. 111, 084801 (2013)

MOP097

A Concept for Seeding 4-40 nm FEL Radiation at FLASH2

electron, laser, FEL, bunching

286

K.E. Hacker
DELTA, Dortmund, Germany

Funding: Work supported by BMBF (contract 05K13PE3)
This note describes a scheme to seed the FLASH2 FEL over a range of 4-40 nm without impacting SASE capabilities. This scheme combines multiple seeding techniques, builds on current infrastructure and offers a maximized range of performance with higher pulse energies than what are available at lower-peak current facilities. The concept relies on Echo Enabled Harmonic Generation (EEHG), cascaded seeding, and Second Harmonic Afterburners (SHAB) while maintaining the possibility to operate with High Gain Harmonic Generation (HGHG) seeding at >30 nm wavelengths.

MOC01

Circular Polarization Control by Reverse Undulator Tapering

FEL, resonance, bunching, electron

297

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

In order to produce circularly polarized light at X-ray FEL facilities one can consider an installation of a short helical (or cross-planar) afterburner, but then one should have an efficient method to suppress powerful linearly polarized background from the main undulator. We propose a new method for such a suppression: an application of the reverse taper in the main undulator. We discover that in a certain range of the taper strength, the density modulation (bunching) at saturation is practically the same as in the case of non-tapered undulator while the power of linearly polarized radiation is suppressed by orders of magnitude. Then strongly modulated electron beam radiates at full power in the afterburner. Considering SASE3 undulator of the European XFEL as a practical example, we demonstrate that soft X-ray radiation pulses with peak power in excess of 100 GW and an ultimately high degree of circular polarization can be produced. The method can be used at different X-ray FEL facilities, in particular at LCLS after installation of the helical afterburner in the near future.

Slides MOC01 [1.545 MB]

MOC03

Radiation Properties of Tapered Hard X-ray Free Electron Lasers

radiation, electron, FEL, simulation

300

C. Emma, C. Pellegrini
UCLA, Los Angeles, USA
S.D. Chen
NCTU, Hsinchu, Taiwan
K. Fang, C. Pellegrini, J. Wu
SLAC, Menlo Park, California, USA
S. Serkez
DESY, Hamburg, Germany

We perform an analysis of the transverse coherence of the radiation from a TW level tapered hard X-ray Free Electron Laser (FEL). The radiation properties of the FEL are studied for a Gaussian, parabolic and uniform transverse electron beam density profile in a 200-m undulator at a resonant wavelength of 1.5 Angstrom. Simulations performed using the 3-D FEL particle code GENESIS show that diffraction of the radiation occurs due to a reduction in optical guiding in the tapered section of the undulator. This results in an increasing transverse coherence for all three transverse electron beam profiles. We determine that for each case considered the radiation coherence area is much larger than the electron beam spot size, making X-ray diffraction experiments possible for TW X-ray FELs.

Slides MOC03 [3.797 MB]

MOC04

Chirped and Modulated Electron Pulse Free Electron Laser Techniques

electron, radiation, FEL, simulation

303

J. Henderson, L.T. Campbell, B.W.J. MᶜNeil
USTRAT/SUPA, Glasgow, United Kingdom

Funding: We acknowledge STFC MoA 4132361; ARCHIE-WeSt HPC, EPSRC grant EP/K000586/1; John von Neumann Institute for Computing (NIC) on JUROPA at Jlich Supercomputing Centre (JSC), under project HHH20
A potential method to improve the free electron laser's output when the electron pulse has a large energy spread is investigate and results presented. A simplified model is the first given, in which there are a number of linearly chirped beamlets equally separated in energy and time. By using chicanes, radiation from one chirped beamlet is passed to the next, helping to negate the effect of the beamlet chirps and maintaining resonant interactions. Hence the addition of chicane allow the electrons to interact with a smaller range of frequencies (Δ ω <2 ρ γ_r), sustaining the FEL interaction. One method to generate such a beamlet structure is presented and is shown to increase FEL performance by two orders of magnitude.

Slides MOC04 [6.777 MB]

TUB01

Review of Coherent SASE Schemes

electron, FEL, bunching, experiment

327

B.W.J. MᶜNeil, L.T. Campbell, J. Henderson
USTRAT/SUPA, Glasgow, United Kingdom
D.J. Dunning, N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Funding: We acknowledge STFC Agreement No. 4163192; ARCHIE-WeSt HPC, EPSRC grant EP/K000586/1; John von Neumann Institute for Computing (NIC) on JUROPA at Julich Supercomputing Centre (JSC), project HHH20
A review is presented of some of the methods and their origins that have recently been proposed to improve the temporal coherence of SASE output. These methods do not require any external laser seed field, or the use of the so-called self-seeding methods, where the SASE radiation is optically filtered and improved at an early stage of the interaction before re-injection and amplification to saturation. By using methods that introduce an additional relative propagation between the electron beam and the radiation field, the localised collective interaction, which leads to the formation of the ‘spiking’ associated with normal SASE output, is removed. The result is output pulses which are close to the fourier transform limit without the need for any external seeds or intermediate optics.

Slides TUB01 [6.256 MB]

TUP006

Two-color Free-electron Laser via Two Orthogonal Undulators

FEL, polarization, electron, radiation

358

N.S. Mirian
IPM, Tehran, Iran
G. Dattoli
ENEA C.R. Frascati, Frascati (Roma), Italy
V. Petrillo
Universita' degli Studi di Milano, Milano, Italy

An amplifier Free electron Laser (FEL) including two orthogonal polarized undulators with different periods and field intensities is able to emit two color radiations with different frequency and polarization while the total length of device does not change respect to usual single color FELs. The wavelengths of two different colors can be changed by choosing different periods, while variation in the magnetic strengths can be used to modify the gain lengths.

TUP007

Spectral Limits and Frequency Sum-rule of Current and Radiation Noise Measurement

electron, radiation, distributed, FEL

362

A. Gover, R. Ianconescu
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
A. Nause
UCLA, Los Angeles, USA

Funding: This research was supported by a grant from the United States-Israel Binational Science Foundation(BSF), Jerusalem, ISRAEL
The current noise spectrum of an electron beam is generally considered white and expressed by the shot-noise formula (eI0). It is possible to control the spectral energy of a random electron beam current by longitudinal space charge microdynamics and dispersive transport. Both noise suppression (relative to eI0)[1,2] and noise enhancement[3] have been demonstrated, exhibiting sub/super-Poissonian particle distribution statistics, respectively. We present a general theory for the current noise of an e-beam and its radiation emission in the entire spectrum. The measurable current noise spectrum is not white. It is cut-off at high frequencies, limited by the measurement length and the beam axial momentum spread (fundamentally limited by quantum uncertainty). We show that under certain conditions the current noise spectrum satisfies a frequency sum-rule: exhibiting noise enhancement in one part of the spectrum when suppressed at another part and vice versa. The spontaneous emission (radiation noise) into a single radiation mode or single direction in any scheme (OTR, Undulator etc.) is sub-radiant when the beam current is sub-Poissonian and vice versa, but the sum-rule does not apply.

TUP012

Numerical Simulation of a Super-radiant THz Source Driven by Femtosecond Electron Bunches

electron, FEL, radiation, emittance

374

R.V. Chulkov
B.I. Stepanov Institute of Physics, Belarus, Russia
V.A. Goryashko
Uppsala University, Uppsala, Sweden
V. Zhaunerchyk
University of Gothenburg, Gothenburg, Sweden

Funding: We would like to acknowledge the financial support from the Swedish FEL center.
Pulsed THz FELs are typically driven by rf Linacs which produce intense electron bunches with a duration of a few picoseconds or even shorter. When the bunch duration is less than a picosecond, the wavelength of the THz light is greater than the bunch length and the FEL operates in the super-radiant (SR) regime*. In the report, we summarize our studies performed for an SR source operating in the THz frequency range. In particular, we focus on an open-type planar undulator comprising no guiding structure. Using a numerical code that supports 3D modeling of the SR dynamics as well as statistical properties of electron bunches, we analyze influence of electron bunch parameters on generated THz radiation and reveal some surprising results. More specifically, for the considered undulator configuration, we predict degradation in the angular divergence and spectral broadening of the generated radiation as the electron bunch emittance decreases. We also demonstrate how electron bunch broadening associated with the electron energy spread can eventually be suppressed.
* R. Chulkov, V. Goryashko, and V. Zhaunerchyk, Report III of the series of reports by the Swedish FEL Center and FREIA Group, http://www.diva-portal.org/smash/get/diva2:699684/FULLTEXT01.pdf.

Poster TUP012 [1.553 MB]

TUP015

Radiation and Interaction of Layers in Quasi-plane Electron Bunches Moving in Undulators

radiation, electron, laser, free-electron-laser

388

N. Balal
Ariel University, Ariel, Israel
V.L. Bratman
IAP/RAS, Nizhny Novgorod, Russia

The model of radiating planes (1D radiating gas) consisting of electrons that oscillate and travel with a relativistic translational velocity allows one to develop a simple general theory describing a number of important effects of radiation in a undulator for dense electron bunches formed in photoinjector accelerators. Having based on this method and taking into account both Coulomb and radiation interactions of the planes with an arbitrary density, particle velocity distribution and energy chirp we have found analytically and numerically efficiency and frequency spectrum for coherent spontaneous radiation, including conditions for generation of minimum narrow and very broadband spectra. The developed theory has been applied for estimation of a powerful terahertz radiation source with a moderate energy of electrons.

TUP017

Using Lorentz Transformations for Simulations of Wiggler Superradiance from the Picosecond Electron Bunches

electron, simulation, radiation, scattering

395

A. Malkin, N.S. Ginzburg, A.A. Golovanov, I.V. Zotova
IAP/RAS, Nizhny Novgorod, Russia
V.P. Tarakanov
LPI, Moscow, Russia

Funding: This work was supported by Russian Foundation for Basic Research under Grant No 12-02-01152.
In this paper we present a theoretical analysis of superradiance (SR) from picosecond electron bunches wiggling in periodical undulator field based both on the method of averaged ponderomotive force and on a direct numerical PIC (particle-in-cell) simulation. Within both approaches the analysis takes place in the reference frame co-moving with electrons which allows simplifying the procedure of simulation significantly due to the fact that all the spatial scales including the radiation wavelength, the length of the beam and the length of the pump field pacet into which the undulator field is transformed are of the same order. We show that in the reference frame the SR effect can be interpreted as a formation of the distributed Bragg mirror in the bulk of the electron beam which is effectively reflecting (scattering) the pump wave. A possibility of generation of multimegawatt pulses in terahertz and far infrared wave ranges is demonstrated.

TUP018

Sensitivity Study of a Tapered Free-Electron Laser

FEL, electron, emittance, free-electron-laser

399

A.W.L. Mak, F. Curbis, S. Werin
MAX-lab, Lund, Sweden

The output power of a free-electron laser (FEL) can be greatly enhanced by tapering the undulator line. In this work, a sensitivity study of a tapered FEL is presented. The study is conducted using the numerical simulation code GENESIS and a taper optimization method. Starting from a possible case for the future X-ray FEL at the MAX IV Laboratory in Lund, Sweden, a number of parameters are varied systematically and the impact on the FEL power is investigated. These parameters include the electron beam's initial energy, current, emittance, energy spread, as well as the seed radiation power.

TUP019

Update on the FEL Code Genesis 1.3

electron, radiation, lattice, FEL

403

S. Reiche
PSI, Villigen PSI, Switzerland

The widely used time-dependent code Genesis 1.3 has been modified to address new needs of users worldwide. The existing limitation of tracking isolated slices of the FEL beam has been overcome by keeping the entire electron beam in memory, which is tracked as a whole through the undulator. This modification allows for additional features such as allowing particles to migrate into other slices or applying self-consistent wakefield and space charge models.

TUP020

MINERVA, a New Code to Model Free-Electron Lasers

FEL, electron, experiment, simulation

408

H. Freund, P.J.M. van der Slot
CSU, Fort Collins, Colorado, USA
P.J.M. van der Slot
Mesa+, Enschede, The Netherlands

Simulation codes modelling the interaction of electrons with an optical field inside an undulator are an essential tool for understanding and designing free-electron lasers (FELs). As there exists a large variety of FELs ranging from long-wavelength oscillators using partial wave guiding to soft and hard x-ray FELs that are either seeded or starting from noise, a simulation code should be capable of modelling this huge variety of FEL configurations. A new code under development, named MINERVA, will be capable of modelling such a large variety of FELs. The code uses a modal expansion for the optical field, e.g., a Gaussian expansion for free-space propagation, and an expansion in waveguide modes for propagation at long wavelengths, or a combination of the two for partial guiding at THz frequencies. MINERVA uses the full Newton-Lorentz force equation to track the particles through the optical and magnetic fields. To allow propagation of the optical field outside the undulator and interact with optical elements, MINERVA interfaces with the optical propagation code OPC to model oscillators. Here we describe the main features of MINERVA and give various examples of its capabilities.

TUP021

Recent Updates to the Optical Propagation Code OPC

diagnostics, FEL, electron, free-electron-laser

412

P.J.M. van der Slot, K.J. Boller
Mesa+, Enschede, The Netherlands
P.J.M. van der Slot
CSU, Fort Collins, Colorado, USA

Funding: This research is supported in part by Office of Naval Research Global, grant number N62909-10-1-7151
In order to understand and design free-electron lasers (FELs), simulation codes modeling the interaction of electrons with a co-propagating optical field in the magnetic field of an undulator are essential. However, propagation of the optical field outside the undulator is equally important for evaluation of the optical field at the location of the application or to model FEL oscillators. The optical propagation code OPC provides such capabilities and can interface with FEL gain codes like GENESIS 1.3, MEDUSA and MINERVA. Here we present recent additions and modifications to the code that (i) improves the speed of the code and (ii) extends the modeling capabilities. These include amongst other, inline diagnostics that results in considerable faster runtimes, the ability to convert from free-space modes to guided modes (currently only cylindrical waveguides), and the possibility to determine the spectrum at each transverse location. The latter opens the possibility to include dispersion in the optical propagation. Finally, work is underway to support HDF5 to remain compatible with the upcoming new release of GENESIS 1.3.

TUP022

The Implementation of 3D Undulator Fields in the Unaveraged FEL Simulation Code Puffin

electron, FEL, focusing, simulation

416

J. Henderson, L.T. Campbell, B.W.J. MᶜNeil
USTRAT/SUPA, Glasgow, United Kingdom
A.R. Maier
CFEL, Hamburg, Germany
A.R. Maier
Uni HH, Hamburg, Germany

Funding: We acknowledge STFC MoA 4132361; ARCHIE-WeSt HPC, EPSRC grant EP/K000586/1; John von Neumann Institute for Computing (NIC) on JUROPA at Jlich Supercomputing Centre (JSC), under project HHH20
The FEL simulation code Puffin is modified to include 3D magnetic undulator fields. Puffin, having previously used a 1D undulator field, is modified to accommodate general 3D magnetic fields. Both plane and curved pole undulators have been implemented. The electron motion for both agrees with analytic predictions.

TUP025

TW X-ray Free Electron Laser Optimisation by Transverse Pulse Shaping

electron, FEL, radiation, simulation

425

C. Emma, C. Pellegrini
UCLA, Los Angeles, USA
C. Pellegrini, J. Wu
SLAC, Menlo Park, California, USA

We study the dependence of the peak power of a 1.5 Angstrom TW, tapered X-ray free-electron laser on the transverse electron density distribution. Multidimensional optimization schemes for TW hard X-Ray free electron lasers are applied to the cases of transversely uniform and parabolic electron beam distributions and compared to a Gaussian distribution. The optimizations are performed for a 200 m undulator and a resonant wavelength of 1.5 Angstrom using the fully 3-dimensional FEL particle code GENESIS. The study shows that the flatter transverse electron distributions enhance optical guiding in the tapered section of the undulator and increase the maximum radiation power from a maximum of 1.56 TW for a transversely Gaussian beam to 2.26 TW for the parabolic case and 2.63 TW for the uniform case. Spectral data also shows a 30-70 % reduction in energy deposited in the sidebands for the uniform and parabolic beams compared with a Gaussian.

TUP026

Transverse Coherence Properties of a TGU-based FEL

FEL, electron, radiation, emittance

429

P. Baxevanis, Z. Huang, R.D. Ruth
SLAC, Menlo Park, California, USA
C.B. Schroeder
LBNL, Berkeley, California, USA

The use of a transverse gradient undulator (TGU) is considered an attractive option for FELs driven by electron beams with a relatively large energy spread. In this scheme, a dispersion is introduced in the beam while the undulator poles are inclined so that the undulator field acquires a linear dependence upon the transverse position in the direction of dispersion. By suitably selecting the dispersion and the field gradient, the energy spread effect can be significantly mitigated, thus avoiding a drastic reduction in the FEL gain. However, adding the dispersion typically leads to electron beams with large aspect ratios. As a result, the presence of higher-order modes in the output FEL radiation can become significant. To investigate this effect, we study the properties of the higher-order eigenmodes of a TGU-based, high-gain FEL, using both a simplified, analytically-solvable model and a variational technique. This formalism is then used to provide an estimate of the degree of transverse coherence for a representative soft X-ray, TGU FEL example.

TUP027

Initial Value Problem for an FEL Driven by an Asymmetric Electron Beam

FEL, electron, radiation, simulation

433

P. Baxevanis, R.D. Ruth
SLAC, Menlo Park, California, USA

FEL configurations in which the driving electron beam is not axially symmetric (round) are important in the study of novel concepts (such as TGU-based FELs) but also become relevant when one wishes to explore the degree to which the deviation from symmetry-inevitable in practical cases-affects the performance of more conventional FEL schemes. In this paper, we present a technique for solving the initial value problem of such an asymmetric FEL. Extending an earlier treatment of ours, we start from a self-consistent, fully 3D, evolution equation for the complex amplitude of the electric field of the FEL radiation, which is then solved by expanding the radiation amplitude in terms of a set of orthogonal transverse modes. The numerical results from such an analysis are in good agreement with simulation and provide a full description of the radiation in the linear regime. Moreover, when the electron beam sizes are constant, this approach can be used to verify the predictions of the standard eigenmode formalism.

TUP028

Mode Contents Analysis of a Tapered Free Electron Laser

FEL, electron, laser, simulation

437

S.D. Chen, K. Fang, X. Huang, C. Pellegrini, J. Wu
SLAC, Menlo Park, California, USA
S.D. Chen, C.-S. Hwang
NCTU, Hsinchu, Taiwan
C. Emma, C. Pellegrini
UCLA, Los Angeles, USA
K. Fang, S.-Y. Lee
Indiana University, Bloomington, Indiana, USA
C.-S. Hwang
NSRRC, Hsinchu, Taiwan
S. Serkez
DESY, Hamburg, Germany

For the ultimate use for the scientific experiments, the free electron laser (FEL) will propagate for long distance, much longer than the Rayleigh range, after exiting the undu- lator. To characterize the FEL for this purpose, we study the electromagnetic field mode components of the FEL photon beam. With the mode decomposition, the transverse coher- ence can be analyzed all along. The FEL here in this paper is a highly tapered one evolving through the exponential growth and then the post-saturation taper. Modes contents are analyzed for electron bunch with three different types of transverse distribution: flattop, Gaussian, and parabolic. The tapered FEL simulation is performed with Genesis code. The FEL photon beam transverse electric field is decom- posed with Gaussian-Laguerre polynomials. The evolutions of spot size, source location, and the portion of the power in the fundamental mode are discussed here. The approach can be applicable to various kind scheme of FEL.

TUP029

iSASE Study

electron, FEL, radiation, simulation

442

K. Fang
Indiana University, Bloomington, Indiana, USA
S.D. Chen
NCTU, Hsinchu, Taiwan
S.D. Chen, K. Fang, X. Huang, C. Pellegrini, J. Wu
SLAC, Menlo Park, California, USA
C. Emma, C. Pellegrini
UCLA, Los Angeles, USA
S. Reiche
PSI, Villigen PSI, Switzerland

Improved Self Amplified Spontaneous Emission (iSASE) is a scheme that reduces FEL bandwidth by increasing phase slippage between the electron bunch and radiation field. This is achieved by repeatedly delaying electrons using phase shifters between undulator sections. Genesis code is modified to facilitate this simulation. With this simulation code, the iSASE bandwidth reduction mechanism is studied in detail. A Temporal correlation function is introduced to describe the similarity between the new grown field from bunching factor and the amplified shifted field. This correlation function indicates the efficiency of iSASE process.

TUP030

Mode Component Evolution and Coherence Analysis in Terawatt Tapered FEL

FEL, electron, radiation, laser

446

K. Fang, S.D. Chen, X. Huang, C. Pellegrini, J. Wu
SLAC, Menlo Park, California, USA
S.D. Chen
NCTU, Hsinchu, Taiwan
C. Emma, C. Pellegrini
UCLA, Los Angeles, USA
K. Fang
Indiana University, Bloomington, Indiana, USA
C.-S. Hwang
NSRRC, Hsinchu, Taiwan
S. Serkez
DESY, Hamburg, Germany

A fast and robust algorithm is developed to decompose FEL radiation field transverse distribution into a set of orthonormal basis. Laguerre Gaussian and Hermite Gaussian can be used in the analysis. The information of mode components strength and Gaussian beam parameters allows users in downstream better utilize FEL. With this method, physics of mode components evolution from starting stage, to linear regime and post saturation are studied with detail. With these decomposed modes, correlation function can be computed with less complexity. Eigenmodes of the FEL system can be solved using this method.

TUP031

FEL Code Comparison for the Production of Harmonics via Harmonic Lasing

FEL, electron, simulation, radiation

451

G. Marcus, W.M. Fawley
SLAC, Menlo Park, California, USA
S. Reiche
PSI, Villigen PSI, Switzerland
E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

Harmonic lasing offers an attractive option to significantly extend the photon energy range of FEL beamlines. Here, the fundamental FEL radiation is suppressed by various combinations of phase shifters, attenuators, and detuned undulators while the radiation at a desired harmonic is allowed to grow linearly. The support of numerical simulations is extensively used in evaluating the performance of this scheme. This paper compares the results of harmonic growth in the harmonic lasing scheme using three FEL codes: FAST, GENESIS, and GINGER.

TUP032

FEL Simulation and Performance Studies for LCLS-II

electron, FEL, simulation, radiation

456

G. Marcus, Y. Ding, P. Emma, Z. Huang, T.O. Raubenheimer, L. Wang, J. Wu
SLAC, Menlo Park, California, USA

The design and performance of the LCLS-II free-electron laser beamlines are presented using start-to-end numerical particle simulations. The particular beamline geometries were chosen to cover a large photon energy tuning range with x-ray pulse length and bandwidth flexibility. Results for self-amplified spontaneous emission and self-seeded operational modes are described in detail for both hard and soft x-ray beamlines in the baseline design.

TUP033

Broadly Tunable Free-Electron Laser for Four-wave Mixing Experiments with Soft X-ray Pulses

electron, FEL, laser, simulation

461

G. Marcus
SLAC, Menlo Park, California, USA
G. Penn
LBNL, Berkeley, California, USA
A. Zholents
ANL, Argonne, Illinois, USA

This paper examines a FEL design for the production of three soft x-ray pulses from a single electron beam suitable for four-wave mixing experiments. Independent control of the wavelength, timing and angle of incidence of the three ultra-short, ultra-intense pulses with exquisite synchronization is critical. A process of selective amplification where a chirped electron beam and a tapered undulator are used to isolate the gain region to only a short fraction of the electron beam is explored in detail. Numerical particle simulations are used to demonstrate the essential features of this scheme in the context of the LCLS-II design study.

TUP035

Investigation of Reverse Taper to Optimize the Degree of Polarization for the Delta Undulator at the LCLS

radiation, polarization, simulation, bunching

465

J.P. MacArthur
Stanford University, Stanford, California, USA
Z. Huang, A. Lutmann, A. Marinelli, T.J. Maxwell, H.-D. Nuhn, D.F. Ratner
SLAC, Menlo Park, California, USA

Funding: U.S. Department of Energy under contract No. DE-AC02-76SF00515
A 3.2 m adjustable phase Delta undulator* will soon be installed on the last girder of the LCLS undulator line. The Delta undulator will act as an afterburner terminating the 33 undulator line, providing arbitrary polarization control to users. Two important figures of merit for users will be the degree of polarization and the x-ray yield. In anticipation of this installation, machine development time at the LCLS was devoted to maximizing the final undulator x-ray contrast and yield with a standard canted pole undulator acting as a stand in for the Delta undulator. Following the recent suggestion** that a reverse taper (dK/dz > 0) in the main undulator line could suppress linearly polarized light generated before an afterburner while still producing the requisite microbunching, we report on a reverse taper study at the LCLS wherein a yield contrast of 15 was measured along the afterburner. We also present 1D simulations comparing the reverse taper technique to other schemes.
* Nuhn, H.-D., Anderson, S., Bowden, G., Ding, Y., Gassner, G., et al., (2013).
** Schneidmiller, E. A. and Yurkov, M. V., Phys. Rev. ST Accel. Beams 16, 110702 (2013).

TUP040

Flying RF Undulator

electron, radiation, resonance, focusing

474

A.V. Savilov, I.V. Bandurkin, S.V. Kuzikov, A.A. Vikharev
IAP/RAS, Nizhny Novgorod, Russia

A new concept for the room-temperature rf undulator, designed to produce coherent X-ray radiation by means of a relatively low-energy electron beam and pulsed mm-wavelength radiation, is proposed. The “flying” undulator is a high-power short rf pulse co-propagating together with a relativistic electron bunch in a helically corrugated waveguide. The electrons wiggle in the rf field of the -1st spatial harmonic with the phase velocity directed in the opposite direction in respect to the bunch velocity, so that particles can irradiate high-frequency Compton’s photons. A high group velocity (close to the speed of light) ensures long cooperative motion of the particles and the co-propagating rf pulse. This work is supported by the Russian Foundation for Basic Research (Projects 14-08-00803 and 14-02-00691).

Poster TUP040 [0.189 MB]

TUP042

High Efficiency Lasing with a Strongly Tapered Undulator

laser, electron, radiation, experiment

478

J.P. Duris, P. Musumeci
UCLA, Los Angeles, California, USA

Funding: This work was supported by DOE grant DE-FG02-92ER40693, Defense of Threat Reduction Agency award HDTRA1-10-1-0073 and University of California Office of the President award 09-LR-04-117055-MUSP.
Typical electrical to optical energy conversion efficiencies for FELs are limited by the Pierce parameter to 10^-3 or smaller. Undulator tapering schemes have enabled extraction of as much as 1 or 2% of the electron energy. Recently, the UCLA BNL helical inverse free electron laser (IFEL) experiment at ATF demonstrated energy doubling and acceleration of 30% of an electron beam from 52 to 93 MeV with a modest 10¹¹ W power CO2 laser pulse. By reversing and retuning the undulator, the electrons may be violently decelerated, thereby transferring energy from the beam to the laser pulse. Simulations show that by sending a 1 kA, 70 MeV electron beam and 100 GW laser into a prebuncher and the reversed undulator, 41% of the electron beam energy should be converted to radiation, allowing the laser pulse power to grow to 127 GW.

TUP045

IFEL Driven Micro-Electro-Mechanical System Free Electron Laser

electron, FEL, laser, radiation

481

N.S. Sudar, J.P. Duris, P. Musumeci
UCLA, Los Angeles, USA

The Free Electron Laser has provided modern science with a tunable source of high frequency, high power, coherent radiation. To date, short wavelength FEL's have required large amounts of space in order to achieve the necessary beam energy to drive the FEL process and to reach saturation of the output radiation power. By utilizing new methods for beam acceleration as well as new undulator technology, we can decrease the space required to build these machines. In this paper, we investigate a scheme by which a tabletop XUV FEL might be realized. Utilizing the Rubicon Inverse Free Electron Laser (IFEL) at BNL together with micro-electro-mechanical system (MEMS) undulator technology being developed at UCLA, we propose a design for a compact XUV FEL.

TUP046

Terahertz FEL based on Photoinjector Beam in RF Undulator

focusing, electron, FEL, radiation

485

S.V. Kuzikov, I.V. Bandurkin, M.E. Plotkin, A.V. Savilov, A.A. Vikharev
IAP/RAS, Nizhny Novgorod, Russia
A.V. Savilov
NNGU, Nizhny Novgorod, Russia

Photoinjectors, which can produce picosecond electron bunches of MeV-level, are attractive for THz generation. Fortunately, a long distance to reach scattering power saturation in FEL is not necessary, if bunch length is shorter than the produced THz half-wavelength. However, the energy of several MeVs does not allow providing long traveling of the flying bunch without longitudinal divergence. That is why, we suggest using specific RF undulator in a form of the normal wave in the helical waveguide at 3 cm wavelength. The mentioned wave has the -1st space harmonic with transverse fields and negative phase velocity (responsible for particle wiggling). This wave has also the 0th harmonic with longitudinal field and positive phase velocity equal to bunch velocity. Due to the synchronous 0th harmonic one can channel low-energy bunches (due to longitudinal focusing field) as far as several meters distance. One might also inject electron bunches in slightly accelerating field, in this case the output THz pulse obtain nearly linear frequency modulation. Such long THz pulses with the mentioned modulation of the frequency can be effectively compressed by pair of diffraction gratings.

Poster TUP046 [2.914 MB]

TUP047

Chirped Pulse Superradiant Free-electron Laser

radiation, electron, laser, FEL

489

Y.-C. Huang, C.H. Chen
NTHU, Hsinchu, Taiwan
J. Wu, Z. Zhang
SLAC, Menlo Park, California, USA

Funding: This work is supported by Ministry of Science and Technology under Contract NSC 102-2112-M-007-002-MY3
When a short electron bunch traverses an undulator and radiates a wavelength significantly longer than the bunch length, the electrons quickly loses energy through so-called superradiance and generate a negatively chirped radiation frequency at the output. In this paper, we develop a theory to describe this chirped-pulse radiation and numerically demonstrate pulse compression by using a quadratic phase filter. As a design example at THz, a photoinjector/linac system generates a 15 MeV electron bunch containing 15-pC charge in a 60-fs duration. The electrons radiate a chirped pulse at 2.5 THz from a 1.5 m long undulator with a period of 5.6 cm and undulator parameter of 1.7. By using a grating pair, the output THz field can be compressed from 27 to 3 cycles. As another example at EUV, a future dielectric laser accelerator [1] is assumed to generate a 100 MeV electron bunch containing 75-fC charge in 1-nm long length. The electrons radiate a chirped EUV pulse at 13.5 nm from a 15.8 cm long dielectric laser undulator [2] with a period of 1.05 mm and undulator field of 3.3 T. By using a quadratic phase filter as a pulse compressor, the peak power of the EUV radiation is increased from 0.7 to 10 kW.
*Y.C. Huang and R.L. Byer, Appl. Phys. Lett. 69 (15), (1996) 2185-2177.
**T. Plettner, R. L. Byer., Phys. Rev. ST Accel. Beams 11, (2008) 030704.

TUP049

Storage Ring XFEL with Longitudinal Focusing

FEL, storage-ring, insertion, optics

492

I.V. Agapov, G. Geloni
XFEL. EU, Hamburg, Germany

In present work we investigate the possibility of running a high gain FEL on a storage ring using a longitudinally focusing insertion to compress bunches passing an undulator. If integrated into a storage ring similar to PETRA III such device could potentially produce continuous ∼1ps pulses of photons in the nm range with peak pulse powers of tens of GW. Even without operating in FEL saturation mode the longitudinal focusing can provide means to increase the brightness and shorten the photon pulse length

TUP057

Development of Compact THz-FEL System at Kyoto University

gun, electron, FEL, simulation

501

S. Suphakul, T. Kii, H. Ohgaki, Y. Tsugamura, H. Zen
Kyoto University, Kyoto, Japan
Q.K. Jia
USTC/NSRL, Hefei, Anhui, People's Republic of China

We are developing a compact accelerator based terahertz (THz) radiation source by free-electron laser (FEL) at the Institute of Advanced Energy, Kyoto University. The system consists of a 1.6 cell BNL type photocathode RF-gun, a focusing solenoid magnet, a magnetic bunch compressor, focusing quadrupoles and an undulator. The system generates an ultra-short electron pulse in a few hundred femtoseconds shorter than radiation wavelength, resulting in super-radiant emission from the undulator. The target radiation wavelength is 100 to 300 μm. A tracking simulation and optimization are performed by using PARMELA and General Particle Tracer (GPT) code. The FEL radiations are analyzed by a 1 dimensional FEL theory. The design parameters, simulation results and status are reported and discussed in this paper.

TUP066

Facility for Coherent THz and FIR Radiation

bunching, FEL, radiation, electron

512

A. Meseck
HZB, Berlin, Germany
V.G. Ziemann
Uppsala University, Uppsala, Sweden

Linac based THz sources are increasingly becoming the method of choice for a variety of research fields, justifying the increasing demand for high repetition rate THz FEL facilities world wide. In particular, pump and probe experiments with THz and IR radiation are of major interest for the user community. In this paper, we propose a facility which accommodates an SRF-linac driven cw THz-FEL in combination with an IR undulator which utilizes the microbunched beam. The layout permits almost perfect synchronization between pump and probe pulse as well as nearly independently tunable THz and IR radiation.

Poster TUP066 [1.655 MB]

TUP082

Coherent Harmonic Generation at the DELTA Storage Ring: Towards User Operation

electron, laser, radiation, experiment

556

A. Meyer auf der Heide, S. Hilbrich, H. Huck, M. Huck, M. Höner, S. Khan, C. Mai, R. Molo, H. Rast, A. Schick, P. Ungelenk
DELTA, Dortmund, Germany

Funding: Work supported by DFG, BMBF, FZ Jülich, and by the Land NRW.
At DELTA, a 1.5-GeV synchrotron light source at the TU Dortmund University, a short-pulse facility based on Coherent Harmonic Generation (CHG) is in operation and shall soon be used for pump-probe experiments. Due to the interaction of ultrashort laser pulses with electron bunches in an undulator, CHG provides short and coherent pulses at harmonics of the laser wavelength. In this paper, recent progress towards user operation, pulse characterization studies such as transverse and longitudinal coherence measurements as well as CHG in the presence of an RF phase modulation are presented.

TUP083

ALPHA – The THz Radiation Source based on AREAL

radiation, electron, FEL, emittance

561

T.L. Vardanyan, G.A. Amatuni, V.S. Avagyan, A. Grigoryan, B. Grigoryan, M. Ivanyan, V.G. Khachatryan, V.H. Petrosyan, V. Sahakyan, A. Sargsyan, A.V. Tsakanian, V.M. Tsakanov, A. Vardanyan, G.S. Zanyan
CANDLE SRI, Yerevan, Armenia

Advanced Research Electron Accelerator Laboratory (AREAL) based on photo cathode RF gun is under construction at the CANDLE. The basic aim of this new facility is to generate sub-picosecond duration electron bunches with an extremely small beam emittance and energies up to 50 MeV. One of the promising directions of the facility development is the creation of ALPHA (Amplified Light Pulse for High-end Applications) experimental stations with coherent radiation source in THz region based on the concept of both conventional undulator and novel radiation sources. The status of the AREAL facility, the main features and outlooks for the ALPHA station are presented in this work.

TUP086

Experiment Preparation Towards a Demonstration of Laser Plasma Based Free Electron Laser Amplification

electron, laser, FEL, free-electron-laser

569

M.-E. Couprie, C. Benabderrahmane, P. Berteaud, C. Bourassin-Bouchet, F. Bouvet, F. Briquez, L. Cassinari, L. Chapuis, M.E. El Ajjouri, C. Herbeaux, N. Hubert, M. Labat, A. Lestrade, A. Loulergue, J. Lüning, O. Marcouillé, J.L. Marlats, F. Marteau, C. Miron, P. Morin, F. Polack, K. Tavakoli, M. Valléau, D. Zerbib
SOLEIL, Gif-sur-Yvette, France
I.A. Andriyash, G. Lambert, V. Malka, C. Thaury
LOA, Palaiseau, France
S. Bielawski, C. Evain, C. Szwaj
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
X. Davoine
CEA/DAM/DIF, Arpajon, France

One direction towards compact Free Electron Laser is to replace the conventional linac by a laser plasma driven beam, provided proper electron beam manipulation to handle the value of the energy spread and of the divergence. Applying seeding techniques also enables to reduce the required undulator length. Rapidly developing Laser Wakefield Accelerators (LWFA) are already able to generate synchrotron radiation. With the presently achieved electron divergence and energy spread an adequate beam manipulation through the transport to the undulator is needed for FEL amplification. A test experiment for the demonstration of FEL amplification with a LWFA is under preparation in the frame of the COXINEL ERC contract in the more general context of LUNEX5. Electron beam transport follows different steps with strong focusing thanks to variable strength permanent magnet quadrupoles, demixing chicane with conventional dipoles, and a second set of quadrupoles for further focusing in the undulator. Progress on the equipment preparation and expected performance are described.

TUP087

The Status of LUNEX5 Project

electron, FEL, laser, operation

574

M.-E. Couprie, C. Benabderrahmane, P. Berteaud, C. Bourassin-Bouchet, F. Bouvet, F. Briquez, L. Cassinari, L. Chapuis, J. Daillant, M. Diop, M.E. El Ajjouri, C. Herbeaux, N. Hubert, M. Labat, P. Lebasque, A. Lestrade, A. Loulergue, P. Marchand, O. Marcouillé, J.L. Marlats, C. Miron, P. Morin, A. Nadji, F. Polack, F. Ribeiro, J.P. Ricaud, P. Roy, K. Tavakoli, M. Valléau, D. Zerbib
SOLEIL, Gif-sur-Yvette, France
S. Bielawski
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
B. Carré, D. Garzella
CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France
X. Davoine
CEA/DAM/DIF, Arpajon, France
N. Delerue
LAL, Orsay, France
G. Devanz, A. Mosnier
CEA/DSM/IRFU, France
A. Dubois, J. Lüning
CCPMR, Paris, France
C. Evain, E. Roussel, C. Szwaj
PhLAM/CERLA, Villeneuve d'Ascq, France
G. Lambert, R. Lehé, V. Malka, A. Rousse, C. Thaury
LOA, Palaiseau, France
C. Madec
CEA/IRFU, Gif-sur-Yvette, France

LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) aims at investigating the production of short, intense, coherent Free Electron Laser (FEL) pulses in the 40-4 nm spectral range. It comprises a 400 MeV superconducting Linear Accelerator for high repetition rate operation (10 kHz), multi-FEL lines and adapted for studies of advanced FEL schemes, a 0.4 - 1 GeV Laser Wake Field Accelerator (LWFA) for its qualification by a FEL application, a single undulator line enabling seeding with High order Harmonic in Gas and echo configurations and pilot user applications. Concerning the superconducting linac, the electron beam dynamics has been modified from a scheme using a third harmonic linearizer and a compression chicane to dog-leg coupled to sextupoles. Besides, the choice of the gun is under revision for fulfilling to 10 kHz repetition rate. Following transport theoretical studies of longitudinal and transverse manipulation of a LWFA electron beam enabling to provide theoretical amplification, a test experiment is under preparation in collaboration with the Laboratoire d’Optique Appliquée towards an experimental demonstration.

TUP088

Free Electron Lasers in 2014

FEL, electron, laser, free-electron-laser

580

J. Blau, K. R. Cohn, W.B. Colson, W.W. Tomlinson
NPS, Monterey, California, USA

Funding: This work has been supported by the Office of Naval Research and the High Energy Laser Joint Technology Office.
Thirty-eight years after the first operation of the short wavelength free electron laser (FEL) at Stanford University, there continue to be many important experiments, proposed experiments, and user facilities around the world. Properties of FELs in the infrared, visible, UV, and x-ray wavelength regimes are tabulated and discussed.

TUP089

The Turkish Accelerator and Radiation Laboratory in Ankara (TARLA) Project

electron, FEL, radiation, linac

585

A.A. Aksoy, Ö. Karslı, C. Kaya, O. Yavaş
Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey
P. Arıkan
Gazi University, Faculty of Arts and Sciences, Teknikokullar, Ankara, Turkey
S. Özkorucuklu
Istanbul University, Istanbul, Turkey

Funding: Work is supported by Ministry of Development of Turkey with Grand No: DPT2006K-120470
The Turkish Accelerator and Radiation Laboratory in Ankara (TARLA) which is proposed as a first facility of Turkish Accelerator Center (TAC) Project will operate two Infra-Red Free Electron Lasers (IR-FEL) covering the range of 3-250 microns. The facility will consist of an injector fed by a thermionic triode gun with two-stage RF bunch compression, two superconducting accelerating modules operating at continuous wave (CW) mode and two independent optical resonator systems with different undulator period lengths. The electron beam will also be used to generate Bremsstrahlung radiation. The facility aims to be first user laboratory in the region of Turkey in which both electromagnetic radiation and particles will be used. In this paper, we discuss design goals of the project and present status and road map of the project.

TUP095

Design of a Compact Light Source Accelerator Facility at IUAC, Delhi

electron, gun, radiation, laser

596

S. Ghosh, R.K. Bhandari, G.K. Chaudhari, D. Kanjilal, J. Karmakar, N. Kumar, A. Pandey, P. Patra, A. Rai, B.K. Sahu
IUAC, New Delhi, India
A.S. Aryshev, J. Urakawa
KEK, Ibaraki, Japan
A. Deshpande, T.S. Dixit
SAMEER, Mumbai, India
V. Naik, A. Roy
VECC, Kolkata, India

Funding: * The project is supported jointly by Board of Research in Nuclear Sciences and Inter University Accelerator Center
The demand for a light source with high brightness and short pulse length from the researchers in the field of physical, chemical, biological and medical sciences is growing in India. To cater to the experimental needs of multidisciplinary sciences, a project to develop a compact Light Source at Inter University Accelerator Centre (IUAC) has been taken up. In the first phase of the project, prebunched [1] electron beam of ~ 8 MeV will be produced by a photocathode RF gun and coherent THz radiation will be produced by a short undulator magnet. In the second phase, the energy of the electron beam will be increased up to 50 MeV by two sets of superconducting niobium resonators. The coherent IR radiation will be produced by using an undulator magnet (conventional method) and X-rays by Inverse Compton Scattering. To increase the average brightness of the electromagnetic radiation, fabrication of superconducting RF gun is going to be started in a parallel development. In this paper the detailed design of the LSI accelerator complex as well as construction timetable will be presented. The physical principles of THz generation and major accelerator subsystems will be discussed.
[1] S. Liu & J.Urakawa, Proc. of FEL 2011, page-92

TUC01

Hard X-ray Self-Seeding Setup and Results at SACLA

electron, FEL, radiation, photon

603

T. Inagaki, N. Adumi, T. Hara, T. Ishikawa, R. Kinjo, H. Maesaka, Y. Otake, H. Tanaka, T. Tanaka, K. Togawa, M. Yabashi
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
S. Goto, Y. Inubushi, T.K. Kameshima, T. Ohata, K. Tono
JASRI/SPring-8, Hyogo, Japan
T. Hasegawa, S. Tanaka
SES, Hyogo-pref., Japan
H. Kimura, A. Miura, H. Ohashi, H. Yamazaki
Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), Hyogo, Japan

In order to improve the spectral and temporal properties of XFEL, the self-seeding option based on the transmission crystal optics has been implemented in SACLA since 2012. The self-seeding setup composed of four dipole magnets that can generate up to 50 fs temporal delay and a diamond single crystal with the thickness of 180 micro-m has been installed at the position of the 9th undulator segment, which has been moved downstream. In 2013, the installation of all the components has been completed in August and the commissioning has been started in October. After a number of tuning processes such as the beam collimation and undulator K-value optimization, significant spectral narrowing has been confirmed at 10 keV with the C(400) Bragg reflection. The spectral bandwidth of seeded FEL is about 3 eV, which is nearly one order narrower than that of SASE measured without the diamond crystal. The peak spectral intensity of seeded FEL is about 5 times higher than that of SASE. Systematic optimization on beam properties is now in progress towards experimental use of seeded XFELs. This talk gives the overview of the plan, achieved results and ongoing R&D.

Slides TUC01 [20.337 MB]

WEB03

European XFEL Construction Status

photon, electron, laser, diagnostics

623

W. Decking
DESY, Hamburg, Germany
F. Le Pimpec
XFEL. EU, Hamburg, Germany

The European XFEL is presently constructed in the Hamburg region, Germany. It aims at producing X-rays in the range from 260 eV up to 24 keV out of three undulators that can be operated simultaneously with up to 27000 pulses/second. The FEL is driven by a 17.5 GeV linear accelerator based on TESLA-type superconducting accelerator modules. This paper presents the status of major components, the present project schedule and a summary of beam parameters that are adapted to the evolving needs of the users.

Slides WEB03 [12.982 MB]

WEB04

The New IR FEL Facility at the Fritz-Haber-Institut in Berlin

FEL, electron, cavity, radiation

629

W. Schöllkopf, W. Erlebach, S. Gewinner, H. Junkes, A. Liedke, G. Meijer, A. Paarmann, G. von Helden
FHI, Berlin, Germany
H. Bluem, D. Dowell, R. Lange, J. Rathke, A.M.M. Todd, L.M. Young
AES, Princeton, New Jersey, USA
S.C. Gottschalk
STI, Washington, USA
U. Lehnert, P. Michel, W. Seidel, R. Wünsch
HZDR, Dresden, Germany

A mid-infrared oscillator FEL has been commissioned at the Fritz-Haber-Institut. The accelerator consists of a thermionic gridded gun, a subharmonic buncher and two S-band standing-wave copper structures [1,2]. It provides a final electron energy adjustable from 15 to 50 MeV, low longitudinal (<50 keV-ps) and transverse emittance (<20 π mm-mrad), at more than 200 pC bunch charge with a micro-pulse repetition rate of 1 GHz and a macro-pulse length of up to 15 μs. Regular user operation started in Nov. 2013 with 6 user stations. Pulsed radiation with up to 100 mJ macro-pulse energy at about 0.5% FWHM bandwidth is routinely produced in the wavelength range from 4 to 48 μm. We will describe the FEL design and its performance as determined by IR power, bandwidth, and micro-pulse length measurements. Further, an overview of the new FHI FEL facility and first user results will be given. The latter include, for instance, spectroscopy of bio-molecules (peptides and small proteins) conformer selected or embedded in superfluid helium nano-droplets at 0.4 K, as well as vibrational spectroscopy of mass-selected metal-oxide clusters and protonated water clusters in the gas phase.
[1] W. Schöllkopf et al., MOOB01, Proc. FEL 2012.
[2] W. Schöllkopf et al., WEPSO62, Proc. FEL 2013.

Slides WEB04 [12.785 MB]

WEB05

FLASH: First Soft X-ray FEL Operating Two Undulator Beamlines Simultaneously

electron, operation, laser, photon

635

K. Honkavaara, B. Faatz, J. Feldhaus, S. Schreiber, R. Treusch, M. Vogt
DESY, Hamburg, Germany

FLASH, the free electron laser user facility at DESY (Hamburg, Germany), has been upgraded with a second undulator beamline FLASH2. After a shutdown to connect FLASH2 to the FLASH linac, FLASH1 is back in user operation since February 2014. Installation of the FLASH2 electron beamline has been completed early 2014, and the first electron beam was transported into the new beamline in March 2014. The commissioning of FLASH2 takes place in 2014 parallel to FLASH1 user operation. This paper reports the status of the FLASH facility, and the first experience of operating two FEL beamlines.

Slides WEB05 [2.481 MB]

THA02

Experimental Characterization of FEL Polarization Control with Cross Polarized Undulators

polarization, FEL, radiation, controls

644

E. Ferrari, E. Allaria, G. De Ninno, B. Diviacco, D. Gauthier, L. Giannessi, G. Penco, C. Spezzani
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
J. Buck, M. Ilchen
XFEL. EU, Hamburg, Germany
G. De Ninno, D. Gauthier
University of Nova Gorica, Nova Gorica, Slovenia
L. Giannessi
ENEA C.R. Frascati, Frascati (Roma), Italy
Z. Huang, A.A. Lutman
SLAC, Menlo Park, California, USA
G. Lambert, B. Mahieu
LOA, Palaiseau, France
J. Viefhaus
DESY, Hamburg, Germany

Polarization control of the coherent radiation is becoming an important feature of recent and future short wavelength free electron laser facilities. While polarization tuning can be achieved taking advantage of specially designed undulators, a scheme based on two consecutive undulators emitting orthogonally polarized fields has also been proposed. Developed initially in synchrotron radiation sources, crossed polarized undulator schemes could benefit from the coherent emission that characterize FELs. In this work we report the first detailed experimental characterization of the polarization properties of an FEL operated with crossed polarized undulators in the Soft-X-Rays. Aspects concerning the average degree of polarization and the shot to shot stability are investigated together with a comparison of the performance of various schemes to control and switch the polarization

Slides THA02 [5.383 MB]

THA03

A Plan for the Development of Superconducting Undulator Prototypes for LCLS-II and Future FELs

FEL, linac, vacuum, electron

649

P. Emma, N.R. Holtkamp, H.-D. Nuhn
SLAC, Menlo Park, California, USA
D. Arbelaez, J.N. Corlett, S.A. Myers, S. Prestemon, D. Schlueter
LBNL, Berkeley, California, USA
C.L. Doose, J.D. Fuerst, E. Gluskin, Q.B. Hasse, Y. Ivanyushenkov, M. Kasa, G. Pile, E. Trakhtenberg
ANL, Argonne, Ilinois, USA

Funding: Work supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515, DE-AC02-05CH11231, and DE-AC02-06CH11357.
Undulators serve as the primary source of radiation for modern storage rings, and more recently for the advent of Free-Electron Lasers (FELs). The performance of future FELs can be greatly enhanced using the much higher magnetic fields of superconducting undulators (SCU). For example, the LCLS-II hard x-ray undulator can be shortened by up to 70 m using an SCU in place of a PMU (permanent magnet undulator), or its spectral performance can be critically improved when using a similar length. In addition, SCUs are expected to be orders of magnitude less sensitive to radiation dose; a major issue at LCLS-II with its 1-MHz electron bunch rate. We present a funded R&D collaboration between SLAC, ANL, and LBNL, which aims to demonstrate the viability of superconducting undulators for FELs by building, testing, measuring, and tuning two 1.5-m long planar SCU prototypes using two different technologies: NbTi at ANL and Nb3Sn at LBNL. Our goal is to review and reassess the LCLS-II HXR baseline plans (PMU) in July of 2015, after the development and evaluation of both prototypes, possibly in favor of an SCU for LCLS-II.

Slides THA03 [29.468 MB]

THB04

Electron Beam Diagnostics and Feedback for the LCLS-II

cavity, feedback, diagnostics, controls

666

J.C. Frisch, P. Emma, A.S. Fisher, P. Krejcik, H. Loos, T.J. Maxwell, T.O. Raubenheimer, S.R. Smith
SLAC, Menlo Park, California, USA

Funding: work supported by DOE contract DE-AC02-76-SF00515
The LCLS_II is a CW superconducting accelerator driven, hard and soft X-ray Free Electron Laser which is planned to be constructed at SLAC. It will operate with a variety of beam modes from single shot to approximately 1 MHz CW at bunch charges from 10pc to 300pC with average beam powers up to 1.2 MW. A variety of types of beam instrumentation will be used, including stripline and cavity BPMS, fluorescent and OTR based beam profile monitors, fast wire scanners and transverse deflection cavities. The beam diagnostics system is designed to allow tuning and continuous measurement of beam parameters, and to provide signals for fast beam feedbacks.

Slides THB04 [1.501 MB]

THP014

Cyclotron-Undulator Cooling of a Free-Electron-Laser Beam

electron, radiation, cyclotron, FEL

710

A.V. Savilov, I.V. Bandurkin, S.V. Kuzikov
IAP/RAS, Nizhny Novgorod, Russia

We propose methods of fast cooling of an electron beam, based on wiggling of particles in an undulator in presence of an axial magnetic field. We use a strong dependence of the axial electron velocity on the oscillatory velocity, when the electron cyclotron frequency is close to the frequency of electron wiggling in the undulator field. Such cooling may open a way for creating a compact X-ray free-electron laser based on the stimulated scattering of a powerful laser pulse on a moderately-relativistic (several MeV) electron beam. This work is supported by the Russian Foundation for Basic Research (Projects 14-08-00803 and 14-02-00691).

Poster THP014 [0.166 MB]

THP018

The Seed Laser System for the Proposed VUV FEL Facility at NSRRC

laser, FEL, electron, radiation

718

M.C. Chou, N.Y. Huang, W.K. Lau, A.P. Lee
NSRRC, Hsinchu, Taiwan

The possibility of establishing a free electron laser facility in Taiwan has been a continuing effort at NSRRC in the past several years. The baseline design of the envisioned NSRRC FEL is a high gain harmonic generation (HGHG) FEL seeded by a 266 nm laser. The seed laser is produced by adding an optical parametric amplification (OPA) system pumped by upgrading the existing IR laser system. To provide broad tunability of the FEL radiation, the seed laser will be tunable. The spectrum considered for seeding the FEL is between 266 - 800 nm with peak power of 200 MW. The spatial and temporal overlap between the sub-100 fs electron bunch and the 100 fs UV seed laser is under study.

Poster THP018 [0.152 MB]

THP025

Linear Accelerator Design for the LCLS-II FEL Facility

linac, electron, FEL, laser

743

P. Emma, J.C. Frisch, Z. Huang, H. Loos, A. Marinelli, T.J. Maxwell, Y. Nosochkov, T.O. Raubenheimer, L. Wang, J.J. Welch, M. Woodley
SLAC, Menlo Park, California, USA
J. Qiang, M. Venturini
LBNL, Berkeley, California, USA
A. Saini, N. Solyak
Fermilab, Batavia, Illinois, USA

Funding: Work supported by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515.
The LCLS-II is an FEL facility proposed in response to the July 2013 BESAC advisory committee, which recommended the construction of a new FEL light source with a high-repetition rate and a broad photon energy range from 0.2 keV to at least 5 keV. A new CW 4-GeV electron linac is being designed to meet this need, using a superconducting (SC) L-band (1.3 GHz) linear accelerator capable of operating with a continuous bunch repetition rate up to 1 MHz at ~16 MV/m. This new 700-m linac is to be built at SLAC in the existing tunnel, making use of existing facilities and providing two separate FELs, preserving the operation of the existing FEL, which can be fed from either the existing copper or the new SC linac. We briefly describe the acceleration, bunch compression, beam transport, beam switching, and electron beam diagnostics. The high-power and low-level RF, and cryogenic systems are described elsewhere.

Poster THP025 [0.627 MB]

THP029

MOGA OPTIMIZATION DESIGN OF LCLS-II LINAC CONFIGURATIONS

linac, emittance, FEL, simulation

763

L. Wang, P. Emma, Y. Nosochkov, T.O. Raubenheimer, M. Woodley, F. Zhou
SLAC, Menlo Park, California, USA
C. F. Papadopoulos, J. Qiang, M. Venturini
LBNL, Berkeley, California, USA

The Linac Coherent Light Source II (LCLS-II) will generate extremely intense X-ray flashes to be used by researchers from all over the world. The FEL is powered by 4 GeV superconducting linear accelerator, operating with a 1 MHz bunch repetition rate. LCLS-II will provide large flexibility in bunch charge and peak current. Multi-Objective Genetic Algorithm (MOGA) is applied to optimize the machine parameters including bunch compressors system, linearizer, de-chirper, RF phase and laser heater, in order to minimize the energy spread, collective effects and emittance. The strong resistive wall wake field along the 2km bypass beam line acts as a natural de-chirper. This paper summarizes the optimization of various configurations.

Poster THP029 [0.702 MB]

THP059

The Laser Heater System of SwissFEL

laser, electron, emittance, operation

871

M. Pedrozzi, M. Calvi, R. Ischebeck, S. Reiche, C. Vicario
PSI, Villigen PSI, Switzerland
B.D. Fell, N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Short wavelength FELs are generally driven by high-brilliance photo-cathode RF-guns which generate electron beams with an uncorrelated energy spread on the order of 1 keV or less. These extremely cold beams can easily develop micro-bunching instabilities caused by longitudinal space charge forces after the compression process. This can result in a blow up of the energy spread and emittance beyond the tolerable level for SASE emission. It has been demonstrated theoretically and experimentally [1] that a controlled increase of the uncorrelated energy spread to typically a few keV is sufficient to strongly reduce the instability growth. In the laser heater system, one achieves a controlled increase of the beam energy spread by a resonant interaction of the electron beam with a transversally polarized laser beam inside of an undulator magnet. The momentum modulation resulting from the energy exchange within the undulator is consequently smeared out in the transmission line downstream of the laser heater system. In SwissFEL, the laser heater system is located after the first two S-band accelerating structures at a beam energy of 150 MeV. This paper describes the layout and the sub-components of this system.
[1] Z. Huang, et al, Phys. Rev. Special Topics – Accelerator and beams 13, 020703 (2010)

THP073

Optics Measurements at FLASH2

optics, extraction, linac, emittance

902

M. Scholz, B. Faatz, M. Vogt, J. Zemella
DESY, Hamburg, Germany

FLASH2 is a newly build second beam line at FLASH, the soft X-ray FEL at DESY, Hamburg. Unlike the existing beam line FLASH1, it is equipped with variable gap undulators. This beam line is currently being commissioned. Both undulator beam lines of FLASH are driven by a common linear accelerator. Fast kickers and a septum are installed at the end of the linac to distribute the electron bunches of every train between FLASH1 and FLASH2. A specific beam optic in the extraction arc with horizontal beam waists in the bending magnets is mandatory in order to mitigate CSR effects. Here we will show first results of measurements and compare to simulations.

THP087

Electron Beam Diagnostics for COXINEL

electron, diagnostics, plasma, FEL

937

M. Labat, C. Bourassin-Bouchet, L. Cassinari, M.-E. Couprie, M.E. El Ajjouri, N. Hubert, A. Loulergue
SOLEIL, Gif-sur-Yvette, France

On the path towards more compact free electron lasers (FELs), the project COXINEL was recently funded: a transfer line will be installed to adapt a plasma accelerated beam (from LOA) into an in-vacuum undulator built by SOLEIL. This experiment should enable to demonstrate the first FEL based on a plasma accelerator. Because plasma beams are intrinsically very different from RF acceletor beams (much shorter, divergent and smaller with a higher energy spread and energy jitter), their transport and matching in the undulator is critical if willing to obtain a significant amplification. This is why special care has to be taken in the design of the beam diagnostics to be able to measure the transverse beam sizes, energy spread and jitter, emittance and bunch length. For these purposes, several diagnostics will be implemented from the plasma accelerator exit down to the undulator exit. In each station, several screen types will be available and associated to high resolution imaging screens. In this paper, we present the experimental layout and associated simulation of the diagnostics performances.