FEL2014 - List of Keywords (emittance)

Paper	Title	Other Keywords	Page
MOP052	Update on FEL Performance for SwissFEL	FEL, undulator, simulation, radiation	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.

TUP012	Numerical Simulation of a Super-radiant THz Source Driven by Femtosecond Electron Bunches	electron, undulator, FEL, radiation	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]

TUP018	Sensitivity Study of a Tapered Free-Electron Laser	FEL, electron, undulator, 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.

TUP026	Transverse Coherence Properties of a TGU-based FEL	FEL, electron, undulator, radiation	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.

TUP083	ALPHA – The THz Radiation Source based on AREAL	radiation, electron, undulator, FEL	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.

WEB02	Beam Operation of the PAL-XFEL Injector Test Facility	gun, laser, electron, cavity	615
	J.H. Han, S.Y. Baek, M.S. Chae, H. J. Choi, T. Ha, J.H. Hong, J. Hu, W.H. Hwang, S.H. Jung, H.-S. Kang, C. Kim, C.H. Kim, I.Y. Kim, J.M. Kim, S.H. Kim, I.S. Ko, H.-S. Lee, J. Lee, S.J. Lee, W.W. Lee, C.-K. Min, G. Mun, D.H. Na, S.S. Park, S.J. Park, Y.J. Park, Y.G. Son, H. Yang PAL, Pohang, Kyungbuk, Republic of Korea
	The Pohang Accelerator Laboratory X-ray Free electron Laser (PAL-XFEL) project was launched in 2011. This project aims at the generation of X-ray FEL radiation in a range of 0.1 to 10 nm for photon users with a bunch repetition rate of 60 Hz. The machine consists of a 10 GeV normal conducting S-band linear accelerator and five undulator beamlines. The linac and two undulator beamlines will be constructed by the end of 2015 and first FEL radiation is expected in 2016. As a part of preparation for the project, an Injector Test Facility was constructed in 2012. Since December 2012, beam commissioning is being carried out to find optimum operating conditions and to test accelerator components including RF, laser, diagnostics, magnet, vacuum and control. We present the status of beam commissioning and components tests at the test facility.
	Slides WEB02 [10.249 MB]

THP003	Two Charges in the Same Bunch Train at the European XFEL	simulation, laser, operation, solenoid	678
	Y.A. Kot, T. Limberg, I. Zagorodnov DESY, Hamburg, Germany
	The European XFEL has been initially designed for the operation with bunch charge of 1 nC () which was later extended down to 20 pC (). An important upgrade of this extension might be the ability to operate different bunch charges in the same RF pulse. In this paper we assume the nominal design of the XFEL injector which means in particular that both charges in the same RF pulse experience the same solenoid field and are generated by the laser of the same rms size. We discuss the requirements which the combined working points of the injector have to fulfil and show the results of the complete start to end (S2E) and SASE simulations for the simultaneous operation of 250 pC and 500 pC bunch charges. DESY XFEL Project Group "The European X-Ray Free-Electron Laser. Technical Design Report" July 2007 ** W. Decking and T. Limberg "European XFEL. Post-TDR Description" February 2013

THP006	Optimization of the PITZ Photo Injector Towards the Best Achievable Beam Quality	laser, electron, cathode, flattop	685
	M. Khojoyan, M. Krasilnikov, F. Stephan, G. Vashchenko DESY Zeuthen, Zeuthen, Germany
	Funding: The work is supported by the German Federal Ministry of education and Research, project 05K10CHE and RFBR grant 13-02-91323. Uniform 3D ellipsoids are proven to be the best distributions for high brightness charged particle beam applications due to the linear dependence of the space charge fields on the position within the distribution. Such electron bunches have lower emittance and are less sensitive to the machine settings and, therefore, should allow more reliable operation, which is one of the key requirements for single-pass free-electron lasers (FELs). The Photo Injector test facility at DESY, Zeuthen site (PITZ) is optimizing high brightness electron sources for linac based FELs such as the European XFEL. Recent measurements at PITZ using a photocathode laser with a flat-top temporal profile have revealed record low transverse emittance values at different bunch charges. As a next step towards the further improvement of the high quality beams, a cathode laser system, capable of producing quasi-3D ellipsoidal bunches is intended to be used at PITZ. In this work the beam dynamics optimization results for various bunch charges and for flat-top and 3D ellipsoidal cathode laser shapes are presented. For each working point the relative emittance growth is estimated due to possible deviations of the machine parameters.

THP007	Recent Electron Beam Optimization at PITZ	electron, laser, gun, cathode	689
	G. Vashchenko, P. Boonpornprasert, J.D. Good, M. Groß, I.I. Isaev, D.K. Kalantaryan, M. Khojoyan, G. Kourkafas, M. Krasilnikov, D. Malyutin, D. Melkumyan, A. Oppelt, M. Otevřel, T. Rublack, F. Stephan DESY Zeuthen, Zeuthen, Germany G. Asova INRNE, Sofia, Bulgaria G. Pathak Uni HH, Hamburg, Germany D. Richter HZB, Berlin, Germany
	High brightness electron sources for linac based freee-lectron lasers operating at short wavelength such as FLASH and the European XFEL are characterized and optimized at the Photo Injector Test Facility at DESY, Zeuthen site (PITZ). In the last few years PITZ mainly was used to condition RF guns for their later operation at FLASH and the European XFEL. Only limited time could be spent for beam characterization. However, recently we have performed emittance measurements and optimization for a reduced gun accelerating gradient which is similar to the usual operation conditions at FLASH. The results of these measurements are presented in this paper.

THP011	Beam Measurement of Photocathode RF-gun for PAL-XFEL	laser, electron, gun, solenoid	699
	J.H. Hong, M.S. Chae, J.H. Han, H.-S. Kang, C.-K. Min, S.J. Park, Y.J. Park PAL, Pohang, Kyungbuk, Republic of Korea I.S. Ko POSTECH, Pohang, Kyungbuk, Republic of Korea
	The Injector Test Facility (ITF) at Pohang Accelerator Laboratory (PAL) was constructed to develop an injector for the PAL X-ray free-electron laser (PAL-XFEL) project. The PAL-XFEL design requires the injector to produce an electron beam with a slice emittance of 0.4 mm-mrad at the charge of 200 pC. A 4-hole type RF-gun has been successfully fabricated and tested at ITF. In this paper we report the recent beam-measurement results using the RF-gun at ITF. Emittance measurements have been carried out by changing laser and RF parameters.

THP012	Error Analysis for Linac Lattice of Hard X-ray FEL Line in PAL-XFEL*	linac, simulation, lattice, alignment	703
	H. Yang, J.H. Han, H.-S. Kang, I.S. Ko PAL, Pohang, Kyungbuk, Republic of Korea
	Funding: *This work was supported by MSIP, Korea. PAL-XFEL consists of the hard x-ray line for 0.06 – 1-nm FEL and the soft x-ray line for 1 – 10-nm FEL. The linac of hard x-ray line is designed to generate 10-GeV, 200-pC, and 3-kA electron beam. It consists of S-band accelerating columns, an X-band linearizer, three bunch compressors (BC). We conduct error simulation in order to evaluate the tolerances of machine parameters and alignments. First, the machine tolerances and beam jitter levels are calculated in the simulations with dynamic errors and we find out the optimized lattice to satisfy the target tolerance of machine. Second, we conduct simulations with misalignment. We quantify the emittance dilution by misalignments, especially those of BCs. In order to compensate the misalignments, the methods of beam correction like Beam Based Alignment (BBA) are presented and the effects of emittance improvements are calculated.
	Poster THP012 [0.736 MB]

THP013	Slice Emittance Measurement using RF Deflecting Cavity at PAL-XFEL ITF	quadrupole, cavity, electron, gun	707
	J. Lee POSTECH, Pohang, Kyungbuk, Republic of Korea J.H. Han, J.H. Hong, I.S. Ko, S.J. Park PAL, Pohang, Kyungbuk, Republic of Korea
	One of key characteristic for operating PAL-XFEL is the time-dependent transverse properties of a bunch, slice emittance. To achieve the design FEL performance of PAL-XFEL a slice emittance of 0.4 mm mrad at 0.2 nC is required. An Injector Test Facility (ITF) was constructed to study beam properties. In addition to projected emittance measurement, slice emittance measurement is being done using a transverse RF deflecting cavity. We presents results of slice emittance measurement at ITF and future plan for the optimization of operating condition.

THP020	Electron Beam Dynamics Optimization Using A Unified Differential Evolution Algorithm	electron, controls, cavity, solenoid	726
	J. Qiang, C.E. Mitchell LBNL, Berkeley, California, USA
	Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231. Accelerator beam dynamics design depends heavily on the use of control parameter optimization to achieve the best performance. In this paper, we report on electron beam dynamics optimization of a model photoinjector using a new unified differential evolution algorithm. We present the new unified differential evolution algorithm and benchmark its performance using several test examples. We also discuss the application of the algorithm in the multi-objective optimization of the photoinjector.

THP022	Theoretical Investigation of Coherent Synchrotron Radiation Induced Microbunching Instability in Transport and Recirculation Arcs	lattice, recirculation, damping, electron	730
	C.-Y. Tsai Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA D. Douglas, R. Li, C. Tennant JLab, Newport News, Virginia, USA
	Funding: This work is supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The coherent synchrotron radiation (CSR) of a high brightness electron beam traversing a series of dipoles, such as recirculation or transport arcs, may lead to the microbunching instability. We extend and develop a semi-analytical approach of the CSR-induced microbunching instability for a general lattice, based on the previous formulation with 1-D CSR model [Phys. Rev. ST Accel. Beams 5, 064401 (2002)] and apply it to investigate the physical processes of microbunching amplification for two example transport arc lattices. We find that the microbunching instability in transport arcs has a distinguishing feature of multistage amplification (e.g, up to 6th stage for our example arcs in contrast to two stage amplification for a 3-dipole chicane). By further extending the concept of stage gain as proposed by Huang and Kim [Phys. Rev. ST Accel. Beams 5, 074401 (2002)], we developed a method to quantitatively characterize the microbunching amplification in terms of iterative or staged orders that allows the comparison of optics impacts on microbunching gain for different lattices. The parametric dependencies and Landau damping for our example lattices are also studied. Excellent agreement of the gain functions and spectra from Vlasov analysis with results from ELEGANT is achieved which helps to validate our analyses.
	Poster THP022 [1.316 MB]

THP026	Design Study of LCLS Chirp-Control with a Corrugated Structure	wakefield, dipole, simulation, quadrupole	748
	Z. Zhang, K.L.F. Bane, Y. Ding, Z. Huang, R.H. Iverson, T.J. Maxwell, G.V. Stupakov, L. Wang SLAC, Menlo Park, California, USA P. Frigola, M.A. Harrison, M. Ruelas RadiaBeam, Santa Monica, California, USA
	The purpose of this paper is to investigate the use of flat metallic plates with small corrugations as a passive dechirper, studying its effects on beam dynamics. Similar systems have been tested in Pohang and Brookhaven at relatively low energies (~100 MeV) and with relatively long bunches (>1ps) [,]. Four meters of such a structure are being machined by Radiabeam Systems for use in the LCLS with a high energy and femtosecond electron beam. In this paper we use a field matching program to obtain the longitudinal and transverse wakes for the purpose of the LCLS dechirper design. In addition, we fit the longitudinal wake to simple functions, so that one can obtain the wake without resorting to the field matching program. Since the transverse wakes–both dipole and quadrupole wakes–are strong, we include beam dynamics simulations to find the tolerances for injection jitter and misalignment in the LCLS. P. Emma, et al. PRL 112, 034801 ** M. Harrison, et al., NaPAc 2013, Pasadena, USA

THP027	LCLS-II Bunch Compressor Study: 5-Bend Chicane	electron, FEL, radiation, wakefield	755
	D. Khan, T.O. Raubenheimer SLAC, Menlo Park, California, USA
	In this paper, we present a potential design for a bunch compressor consisting of 5 bend magnets which is designed to compensate the transverse emittance growth due to Coherent Synchrotron Radiation (CSR). A specific implementation for the second bunch compressor in the LCLS-II is considered. The design has been optimized using the particle tracking code, ELEGANT. Comparisons of the 5-bend chicane’s performance with that of a symmetric 4-bend chicane are shown for various compression ratios and bunch charges. Additionally, a one-dimensional, longitudinal CSR model for the 5-bend design is developed and its accuracy compared against ELEGANT simulations.
	Poster THP027 [0.881 MB]

THP029	MOGA OPTIMIZATION DESIGN OF LCLS-II LINAC CONFIGURATIONS	linac, undulator, 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]

THP030	Recent Photocathode R&D for the LCLS injector	laser, cathode, gun, vacuum	769
	F. Zhou, A. Brachmann, W.J. Corbett, M.J. Ferreira, S. Gilevich, E.N. Jongewaard, J.R. Lewandowski, J. Sheppard, T. Vecchione, S. Vetter, S.P. Weathersby SLAC, Menlo Park, California, USA
	Funding: US DOE under contract No. DE-AC02-76SF00515 Systematic studies of the copper photocathodes identical to those used in the LCLS injector gun has been carried out at SLAC’s RF gun test facility. Recent observations at the gun test facility indicate that the pre-cleaning of the cathode prior to the installation in the gun is the major cause of the lower initial QE (~10^-6) in the RF gun. All of four cathodes tested in the gun test facility have reliable higher initial QE, 4-8·10^-5, with removal of pre-cleaning step. All of details will be described in the paper. A robust laser-assisted processing recipe has been developed. With this recipe, QE can be repeatedly evolved to about 1x10^-4 within 3-4 weeks following the laser processing, and within 1-2 days the emittance is recovered to the values as observed prior to the laser processing. When compared to previous recipe used for the present LCLS cathode, the new recipe uses lower laser fluence and provides faster emittance recovery. Laser pointing stability is a key requirement for the success of the technique. This paper presents all details of the studies for four cathodes with over a few tens of laser-assisted spots and compares the results with the present LCLS cathode.

THP031	Further Understanding the LCLS Injector Emittance	electron, collimation, laser, radiation	774
	F. Zhou, K.L.F. Bane, Y. Ding, Z. Huang, H. Loos SLAC, Menlo Park, California, USA
	Funding: US DOE under contract No. DE-AC02-76SF00515 Notable COTR effect from the LCLS laser heater chicane is recently observed at the LCLS injector OTR screen, used for routine emittance measurements. The emittance with the OTR screen is under-estimated by about 30% compared to the values with the wire scanner located next to the OTR screen. The emittance with the OTR and wire scanner is compared and relevant analyses are presented. Slice emittance upstream of the LCLS BC1 is measured using a traditional transverse cavity. Recently, slice emittance downstream of the BC1 is able to be measured with a newly developed technique, using a collimator located in the middle of the BC1. The parasitic effects of using the collimator for slice emittance measurement are evaluated. The slice emittance before and after the BC1 is compared. The dependence of the slice emittance on the linearizer’s transverse offset and CSR effect from the BC1 is discussed.

THP037	Beam Performance of the Photocathode Gun for the Max IV Linac	gun, laser, cathode, injection	799
	J. Andersson, F. Curbis, D. Kumbaro, F. Lindau, S. Werin MAX-lab, Lund, Sweden
	The MAX IV facility in Lund (Sweden) is under construction and conditioning of the electron guns for the injector is ongoing. There are two guns in the injector, one thermionic gun for storage ring injection and one photocathode gun for the Short Pulse Facility. In this paper we report on the beam performance tests of the photocathode gun. The measurements were performed at the MAX IV electron gun test stand during spring 2014. Parameters that were studied includes quantum efficiency, emittance and emittance compensation. Results from the measurements are also compared to particle simulations done with ASTRA.

THP039	Commissioning of the Photo-Cathode RF Gun at APS	gun, cathode, laser, solenoid	803
	Y.-E. Sun, J.C. Dooling, R.R. Lindberg, A. Nassiri, S.J. Pasky, H. Shang, T.L. Smith, A. Zholents ANL, Argonne, Ilinois, USA
	A S-band RF gun is recently RF conditioned and commissioned at APS, Argonne. In this paper we report the high-power RF conditioning process of the gun. Dark currents are monitored during the RF conditioning and found to be less than 150pC. Following the RF conditioning, photo-electron beams are generated from the gun and the copper cathode quantum efficiency is monitored. We study the quantum efficiency as gun gradient varies and vacuum condition improves. Photo-electron beam enery and emittance are measured as RF gun gradient and solenoid, as well as drive-laser conditions are varied. Finally we compare our experimental results with numerical simulations. Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.

THP041	Development of All-metal Stacked-double Gate Field Emitter Array Cathodes for X-ray Free-electron Laser Applications	electron, laser, collimation, resonance	811
	S. Tsujino, H.-H. Braun, P. Das Kanungo, V. Guzenko, C. Lee, Y. Oh, M. Paraliev PSI, Villigen PSI, Switzerland T. Feurer Universität Bern, Institute of Applied Physics, Bern, Switzerland
	Funding: This work was partially supported by the Swiss National Science Foundation Nos. 200020₁43428 and 2000021₁47101. We report the design, fabrication, and characterization of all-metal stacked-double-gate field emitter array (FEA) cathodes as a potential upgrade option of SwissFEL cathode at the Paul Scherrer Institute. Single-gate FEAs have demonstrated stable operation and gated field emission in pulsed diode gun with gradient up to 30 MV/m with pulse duration down to 200 ps and generation of 5 pC electron bunches by near infrared laser-induced field emission. However for high brightness applications it is crucial to reduce the beam divergence of individual beamlet by a suitable double-gate structure. The challenge lies in suppressing the concomitant decrease of the emission current when a negative focusing potential is applied to the second gate. To solve this problem, a stacked-double-gate FEAs with large collimation gate aperture diameter has been proposed. The intrinsic transverse emittance evaluated from a beam measurement for 1 mm-diameter FEA was below 0.1 mm-mrad. Compatibility with neon-gas conditioning to improve the beam uniformity and high emission current with double-gate FEAs were also demonstrated recently. The current research is focusing on the combination of the surface-plasmon-polariton resonance of the gate electrode and the near infrared laser-induced field emission to realize an ultrafast and ultrabright FEA cathode.

THP042	The LCLS-II Injector Design	gun, cathode, laser, cavity	815
	J.F. Schmerge, A. Brachmann, D. Dowell, A.R. Fry, R.K. Li, Z. Li, T.O. Raubenheimer, T. Vecchione, F. Zhou SLAC, Menlo Park, California, USA A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA D. Filippetto, R. Huang, C. F. Papadopoulos, G.J. Portmann, J. Qiang, F. Sannibale, S.P. Virostek, R.P. Wells LBNL, Berkeley, California, USA A. Lunin, N. Solyak, A. Vivoli Fermilab, Batavia, Illinois, USA
	The new LCLS-II project will construct a 4 GeV continuous wave (CW) superconducting linear accelerator to simultaneously feed two undulators which will cover the spectral ranges 0.2-1.2 keV and 1-5 keV, respectively. The injector must provide up to 300 pC/bunch with a normalized emittance < 0.6 mm and peak current > 30 A at up to 1 MHz repetition rate. An electron gun with the required brightness at such high repetition rate has not yet been demonstrated. However, several different options have been explored with results that meet or exceed the performance requirements of LCLS-II. The available technologies for high repetition-rate guns, and the need to keep dark current within acceptable values, limit the accelerating gradient in the electron gun. We propose a CW normal conducting low frequency RF gun for the electron source due to a combination of the simplicity of operation and the highest achieved gradient in a CW gun, potentially allowing for lower beam emittances. The high gradient is especially significant at the 300 pC/bunch charge where beam quality can suffer due to space charge. This paper describes the design challenges and presents our solutions for the LCLS-II injector.

THP057	Longitudinal and Transverse Optimization for a High Repetition Rate Injector	gun, electron, cavity, brightness	864
	C. F. Papadopoulos, D. Filippetto, R. Huang, G.J. Portmann, H.J. Qian, F. Sannibale, S.P. Virostek, R.P. Wells LBNL, Berkeley, California, USA A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA A. Brachmann, D. Dowell, P. Emma, Z. Li, T.O. Raubenheimer, J.F. Schmerge, T. Vecchione, F. Zhou SLAC, Menlo Park, California, USA A. Vivoli Fermilab, Batavia, Illinois, USA
	Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 The injector is the low energy part of a linac, where space charge and kinematic effects may affect the electron beam quality significantly, and in the case of single pass systems determines the brightness in the downstream components. Following the increasing demand for high repetition rate user facilities, the VHF-gun, a normal conducting, high repetition rate (1 MHz) RF gun operating at 186 MHz has been constructed at LBNL within the APEX project and is under operation. In the current paper, we report on the status of the beam dynamics studies. For this, a multi-objected approach is used, where both the transverse and the longitudinal phase space quality is optimized, as quantified by the transverse emittance and the bunch length and energy spread respectively. We also report on different bunch charge operating modes.

THP059	The Laser Heater System of SwissFEL	laser, undulator, electron, 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)

THP064	High Repetition Rate S-band Photoinjector Design for the CLARA FEL	gun, cavity, linac, FEL	889
	J.W. McKenzie, L.S. Cowie, P. Goudket, B.L. Militsyn STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom T.J. Jones STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom V.V. Paramonov RAS/INR, Moscow, Russia
	We present the design of a 1.5cell S-band photoinjector RF gun intended to be operated at repetition rates up to 400 Hz in single bunch mode. This gun is intended for use at the proposed CLARA (Compact Linear Accelerator for Research and Applications) FEL test facility at Daresbury Laboratory in the UK and will first be tested and characterised on VELA (Versatile Electron Linear Accelerator) in 2015. The final cavity design is presented including optimisation for CLARA beam dynamics, and choice of a novel coaxial H-shaped coupler.

THP073	Optics Measurements at FLASH2	optics, extraction, undulator, linac	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.

THP075	Design of TDS-based Multi-screen Electron Beam Diagnostics for the European XFEL	kicker, electron, operation, timing	909
	J. Wychowaniak TUL-DMCS, Łódź, Poland C. Gerth, M. Yan DESY, Hamburg, Germany
	Dedicated longitudinal electron beam diagnostics is essential for successful operation of modern free-electron lasers. Demand for diagnostic data includes the longitudinal bunch profile, bunch length and slice emittance of the electron bunches. Experimental setups based on transverse deflecting structures (TDS) are excellent candidates for this purpose. At the Free-Electron Laser in Hamburg (FLASH), such a longitudinal bunch profile monitor utilizing a TDS, a fast kicker magnet and an off-axis imaging screen, has been put into operation. It enables the measurement of a single bunch out of a bunch train without affecting the remaining bunches. At the European X-ray Free-Electron Laser (XFEL) multiscreen stations in combination with TDS are planned to be installed. In order to allow for flexible measurements of longitudinal bunch profile and slice emittance, a configurable timing and trigger distribution to the fast kicker magnets and screen stations is required. In this paper, we discuss various operation patterns and the corresponding realization based on MTCA.4 technology.

THP088	Comparison of Quadrupole Scan and Multi-screen Method for the Measurement of Projected and Slice Emittance at the SwissFEL Injector Test Facility	quadrupole, diagnostics, optics, FEL	941
	M. Yan, B. Beutner, C. Gerth DESY, Hamburg, Germany R. Ischebeck, E. Prat PSI, Villigen PSI, Switzerland
	High-brightness electron bunches with small transverse emittance are required to drive X-ray free-electron lasers (FELs). For the measurement of the transverse emittance, the quadrupole scan and multi-screen methods are the two most common procedures. By employing a transverse deflecting structure, the measurement of the slice emittance becomes feasible. The quadrupole scan is more flexible in freely choosing the data points during the scan, while the multi-screen method allows on-line emittance measurements utilising off-axis screens in combination with fast kicker magnets. The latter is especially the case for high-repetition multi-bunch FELs, such as the European XFEL, which offer the possibility of on-line diagnostics. In this paper, we present comparative measurements of projected and slice emittance applying these two methods at the SwissFEL Injector Test Facility and discuss the implementation of on-line diagnostics at the European XFEL.

THC02	Thermal Emittance Measurements at the SwissFEL Injector Test Facility	cathode, laser, gun, electron	970
	E. Prat, S. Bettoni, H.-H. Braun, M.C. Divall, R. Ganter, C.P. Hauri, T. Schietinger, A. Trisorio, C. Vicario PSI, Villigen PSI, Switzerland C.P. Hauri EPFL, Lausanne, Switzerland
	In a laser-driven RF-gun the ultimate limit of the beam emittance is the transverse momentum of the electrons as they exit the cathode, the so-called intrinsic or thermal emittance. In this contribution we present measurements of the thermal emittance at the SwissFEL Injector Test Facility for electron beam charges down to a few tens of fC. We have studied the thermal emittance and QE dependence on the laser wavelength, the RF-gun gradient and the cathode material (Cu and Cs2Te).
	Slides THC02 [1.063 MB]

THC03	Suppression of the CSR-induced Emittance Growth in Achromats using Two-dimensional point-kick Analysis	dipole, simulation, optics, linear-collider	976
	Y. Jiao, X. Cui, X.Y. Huang, G. Xu IHEP, Beijing, People's Republic of China
	Coherent synchrotron radiation (CSR) effect causes transverse emittance dilution in high-brightness light sources and linear colliders. Suppression of the emittance growth induced by CSR is essential and critical to preserve the beam quality and to help improve the machine performance. To evaluate the CSR effect analytically, we propose a novel method, named “two-dimensional point-kick analysis”. In this method, the CSR-induced emittance growth in an n-dipole achromat can be evaluated with the analysis of only the motion of particle in (x, x') two-dimensional plane with n-point kicks, which can be, to a large extent, counted separately. To demonstrate the effectiveness of this method, the CSR effect in a two-diople achromat and a symmetric TBA is studied, and generic conditions of suppressing the CSR-induced emittance growth, which are independent of concrete element parameters and are robust against the variation of initial beam distribution, are found. These conditions are verified with the ELEGANT simulations and can be rather easily applied to real machines.
	Slides THC03 [1.941 MB]

THC04	Beam Simulations of High Brightness Photocathode DC Gun and Injector for High Repetition FEL Light Source	gun, operation, FEL, cathode	980
	T. Miyajima, Y. Honda, X. Jin, T. Uchiyama, M. Yamamoto KEK, Ibaraki, Japan R. Hajima, R. Nagai, N. Nishimori JAEA, Ibaraki-ken, Japan
	As a next generation FEL light source based on linac, high repetition rate operation to increase average FEL power has been proposed, e.g. LCLS-II project. The injector, which generates high brightness and high average current beam, is one of key components. A photocathode DC gun and superconducting RF cavities, which are developed for ERL light source, can be employed for the high repetition rate injector. For high repetition rate operation of FEL light source, injector simulations were carried out based on ERL injector with demonstrated hardware performance by the cERL beam operation in KEK. The optimization results show that the gun voltage of 500 kV is helpful to achieve low emittance. In addition, to estimate optimum gun voltage and cavity acceleration gradient for the FEL operation, two optimizations with different injector layouts were carried out. The results show that the both different layouts have potential to achieve target emittance for FEL operation. Under the realistic operation condition, the transverse normalized rms emittance of 0.8 mm mrad with the rms bunch length of 3 ps, the bunch charge of 325 pC, and the beam energy of 10 MeV is obtained from the optimizations.
	Slides THC04 [3.796 MB]

FRB02	A Collinear Wakefield Accelerator for a High Repetition Rate Multi-beamline Soft X-ray FEL Facility	wakefield, electron, FEL, acceleration	993
	A. Zholents, W. Gai, R.R. Lindberg, J.G. Power, Y.-E. Sun ANL, Argonne, Ilinois, USA C.-J. Jing, A. Kanareykin Euclid TechLabs, LLC, Solon, Ohio, USA C. Li, C.-X. Tang TUB, Beijing, People's Republic of China D.Y. Shchegolkov, E.I. Simakov LANL, Los Alamos, New Mexico, USA
	Funding: Supported by U.S. Department of Energy under Contract No. DE-AC02-06CH11357 and by the U.S. Department of Energy Laboratory LDRD program at Los Alamos National Laboratory. A concept is presented for a multi beamline soft x-ray free-electron laser (FEL) facility where several FEL undulator lines are driven by an equal number of high repetition rate single-stage collinear wakefield accelerators (CWA). A practical design of the CWA, extending over 30 meters and embedded into a quadrupole wiggler, is considered. The wiggler’s structure of alternating focusing and defocusing quadrupoles is used to control single-bunch breakup instability. It is shown that practical restrictions on the maximum attainable quadrupole field limit the maximum attainable charge in the drive bunch whose sole purpose is to produce a high accelerating field in the CWA for the following main bunch. It is also pointed out that the distance between drive and main bunches varies along the accelerator, causing a measurable impact on the energy gain by the main bunch and on the energy spread of electrons in it. Means to mitigate these effects are proposed and results are presented for numerical simulations demonstrating the main bunch with plausible parameters for FEL application including a relatively small energy spread. Finally, results are presented for the expected FEL performance using an appropriately chosen undulator.
	Slides FRB02 [6.512 MB]

FRB04	Divergence Reduction and Emittance Conservation in a Laser Plasma Acceleration Stage	plasma, laser, acceleration, extraction	999
	A.R. Maier, I. Dornmair CFEL, Hamburg, Germany K. Flöttmann DESY, Hamburg, Germany
	Plasma accelerators promise a compact source of highly relativistic electron beams. Driven by high-intensity lasers or high-energetic electron beams, the longitudinal and transverse electric fields inside the plasma cavitiy support the generation of GeV electron beams over m-scale distances, while measured emittances on the order of 0.1 mm.mrad have been reported from plasma-driven accelerators. However, it remains challenging to conserve this excellent emittance when coupling from the plasma into vacuum and a subsequent beam optics, especially when considering the large energy spread, typically accumulated during the off-crest acceleration inside the plasma. Recently, we presented an analytical solution [1] to describe an adiabatic matching from the plasma into vacuum. Further elaborating this concept [2], we will discuss the generation of low-divergence electron beams from a tailored plasma target in order to preserve the emittance generated within the plasma. We will apply our concept to an externally injected electron bunch, that is matched in and out of a tailored plasma target, generating a GeV-level electron beam with low divergence and good emittance. * K. Floettmann, Phys. Rev. ST - Accel. Beams 17, 054402 (2014) ** I. Dornmair, K. Floettmann, and A. R. Maier, submitted (2014)

Paper

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Other Keywords

Page

MOP052

Update on FEL Performance for SwissFEL

FEL, undulator, simulation, radiation

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.

TUP012

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

electron, undulator, FEL, radiation

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]

TUP018

Sensitivity Study of a Tapered Free-Electron Laser

FEL, electron, undulator, 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.

TUP026

Transverse Coherence Properties of a TGU-based FEL

FEL, electron, undulator, radiation

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.

TUP083

ALPHA – The THz Radiation Source based on AREAL

radiation, electron, undulator, FEL

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.

WEB02

Beam Operation of the PAL-XFEL Injector Test Facility

gun, laser, electron, cavity

615

J.H. Han, S.Y. Baek, M.S. Chae, H. J. Choi, T. Ha, J.H. Hong, J. Hu, W.H. Hwang, S.H. Jung, H.-S. Kang, C. Kim, C.H. Kim, I.Y. Kim, J.M. Kim, S.H. Kim, I.S. Ko, H.-S. Lee, J. Lee, S.J. Lee, W.W. Lee, C.-K. Min, G. Mun, D.H. Na, S.S. Park, S.J. Park, Y.J. Park, Y.G. Son, H. Yang
PAL, Pohang, Kyungbuk, Republic of Korea

The Pohang Accelerator Laboratory X-ray Free electron Laser (PAL-XFEL) project was launched in 2011. This project aims at the generation of X-ray FEL radiation in a range of 0.1 to 10 nm for photon users with a bunch repetition rate of 60 Hz. The machine consists of a 10 GeV normal conducting S-band linear accelerator and five undulator beamlines. The linac and two undulator beamlines will be constructed by the end of 2015 and first FEL radiation is expected in 2016. As a part of preparation for the project, an Injector Test Facility was constructed in 2012. Since December 2012, beam commissioning is being carried out to find optimum operating conditions and to test accelerator components including RF, laser, diagnostics, magnet, vacuum and control. We present the status of beam commissioning and components tests at the test facility.

Slides WEB02 [10.249 MB]

THP003

Two Charges in the Same Bunch Train at the European XFEL

simulation, laser, operation, solenoid

678

Y.A. Kot, T. Limberg, I. Zagorodnov
DESY, Hamburg, Germany

The European XFEL has been initially designed for the operation with bunch charge of 1 nC (*) which was later extended down to 20 pC (**). An important upgrade of this extension might be the ability to operate different bunch charges in the same RF pulse. In this paper we assume the nominal design of the XFEL injector which means in particular that both charges in the same RF pulse experience the same solenoid field and are generated by the laser of the same rms size. We discuss the requirements which the combined working points of the injector have to fulfil and show the results of the complete start to end (S2E) and SASE simulations for the simultaneous operation of 250 pC and 500 pC bunch charges.
* DESY XFEL Project Group "The European X-Ray Free-Electron Laser. Technical Design Report" July 2007
** W. Decking and T. Limberg "European XFEL. Post-TDR Description" February 2013

THP006

Optimization of the PITZ Photo Injector Towards the Best Achievable Beam Quality

laser, electron, cathode, flattop

685

M. Khojoyan, M. Krasilnikov, F. Stephan, G. Vashchenko
DESY Zeuthen, Zeuthen, Germany

Funding: The work is supported by the German Federal Ministry of education and Research, project 05K10CHE and RFBR grant 13-02-91323.
Uniform 3D ellipsoids are proven to be the best distributions for high brightness charged particle beam applications due to the linear dependence of the space charge fields on the position within the distribution. Such electron bunches have lower emittance and are less sensitive to the machine settings and, therefore, should allow more reliable operation, which is one of the key requirements for single-pass free-electron lasers (FELs). The Photo Injector test facility at DESY, Zeuthen site (PITZ) is optimizing high brightness electron sources for linac based FELs such as the European XFEL. Recent measurements at PITZ using a photocathode laser with a flat-top temporal profile have revealed record low transverse emittance values at different bunch charges. As a next step towards the further improvement of the high quality beams, a cathode laser system, capable of producing quasi-3D ellipsoidal bunches is intended to be used at PITZ. In this work the beam dynamics optimization results for various bunch charges and for flat-top and 3D ellipsoidal cathode laser shapes are presented. For each working point the relative emittance growth is estimated due to possible deviations of the machine parameters.

THP007

Recent Electron Beam Optimization at PITZ

electron, laser, gun, cathode

689

G. Vashchenko, P. Boonpornprasert, J.D. Good, M. Groß, I.I. Isaev, D.K. Kalantaryan, M. Khojoyan, G. Kourkafas, M. Krasilnikov, D. Malyutin, D. Melkumyan, A. Oppelt, M. Otevřel, T. Rublack, F. Stephan
DESY Zeuthen, Zeuthen, Germany
G. Asova
INRNE, Sofia, Bulgaria
G. Pathak
Uni HH, Hamburg, Germany
D. Richter
HZB, Berlin, Germany

High brightness electron sources for linac based freee-lectron lasers operating at short wavelength such as FLASH and the European XFEL are characterized and optimized at the Photo Injector Test Facility at DESY, Zeuthen site (PITZ). In the last few years PITZ mainly was used to condition RF guns for their later operation at FLASH and the European XFEL. Only limited time could be spent for beam characterization. However, recently we have performed emittance measurements and optimization for a reduced gun accelerating gradient which is similar to the usual operation conditions at FLASH. The results of these measurements are presented in this paper.

THP011

Beam Measurement of Photocathode RF-gun for PAL-XFEL

laser, electron, gun, solenoid

699

J.H. Hong, M.S. Chae, J.H. Han, H.-S. Kang, C.-K. Min, S.J. Park, Y.J. Park
PAL, Pohang, Kyungbuk, Republic of Korea
I.S. Ko
POSTECH, Pohang, Kyungbuk, Republic of Korea

The Injector Test Facility (ITF) at Pohang Accelerator Laboratory (PAL) was constructed to develop an injector for the PAL X-ray free-electron laser (PAL-XFEL) project. The PAL-XFEL design requires the injector to produce an electron beam with a slice emittance of 0.4 mm-mrad at the charge of 200 pC. A 4-hole type RF-gun has been successfully fabricated and tested at ITF. In this paper we report the recent beam-measurement results using the RF-gun at ITF. Emittance measurements have been carried out by changing laser and RF parameters.

THP012

Error Analysis for Linac Lattice of Hard X-ray FEL Line in PAL-XFEL*

linac, simulation, lattice, alignment

703

H. Yang, J.H. Han, H.-S. Kang, I.S. Ko
PAL, Pohang, Kyungbuk, Republic of Korea

Funding: *This work was supported by MSIP, Korea.
PAL-XFEL consists of the hard x-ray line for 0.06 – 1-nm FEL and the soft x-ray line for 1 – 10-nm FEL. The linac of hard x-ray line is designed to generate 10-GeV, 200-pC, and 3-kA electron beam. It consists of S-band accelerating columns, an X-band linearizer, three bunch compressors (BC). We conduct error simulation in order to evaluate the tolerances of machine parameters and alignments. First, the machine tolerances and beam jitter levels are calculated in the simulations with dynamic errors and we find out the optimized lattice to satisfy the target tolerance of machine. Second, we conduct simulations with misalignment. We quantify the emittance dilution by misalignments, especially those of BCs. In order to compensate the misalignments, the methods of beam correction like Beam Based Alignment (BBA) are presented and the effects of emittance improvements are calculated.

Poster THP012 [0.736 MB]

THP013

Slice Emittance Measurement using RF Deflecting Cavity at PAL-XFEL ITF

quadrupole, cavity, electron, gun

707

J. Lee
POSTECH, Pohang, Kyungbuk, Republic of Korea
J.H. Han, J.H. Hong, I.S. Ko, S.J. Park
PAL, Pohang, Kyungbuk, Republic of Korea

One of key characteristic for operating PAL-XFEL is the time-dependent transverse properties of a bunch, slice emittance. To achieve the design FEL performance of PAL-XFEL a slice emittance of 0.4 mm mrad at 0.2 nC is required. An Injector Test Facility (ITF) was constructed to study beam properties. In addition to projected emittance measurement, slice emittance measurement is being done using a transverse RF deflecting cavity. We presents results of slice emittance measurement at ITF and future plan for the optimization of operating condition.

THP020

Electron Beam Dynamics Optimization Using A Unified Differential Evolution Algorithm

electron, controls, cavity, solenoid

726

J. Qiang, C.E. Mitchell
LBNL, Berkeley, California, USA

Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231.
Accelerator beam dynamics design depends heavily on the use of control parameter optimization to achieve the best performance. In this paper, we report on electron beam dynamics optimization of a model photoinjector using a new unified differential evolution algorithm. We present the new unified differential evolution algorithm and benchmark its performance using several test examples. We also discuss the application of the algorithm in the multi-objective optimization of the photoinjector.

THP022

Theoretical Investigation of Coherent Synchrotron Radiation Induced Microbunching Instability in Transport and Recirculation Arcs

lattice, recirculation, damping, electron

730

C.-Y. Tsai
Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
D. Douglas, R. Li, C. Tennant
JLab, Newport News, Virginia, USA

Funding: This work is supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The coherent synchrotron radiation (CSR) of a high brightness electron beam traversing a series of dipoles, such as recirculation or transport arcs, may lead to the microbunching instability. We extend and develop a semi-analytical approach of the CSR-induced microbunching instability for a general lattice, based on the previous formulation with 1-D CSR model [Phys. Rev. ST Accel. Beams 5, 064401 (2002)] and apply it to investigate the physical processes of microbunching amplification for two example transport arc lattices. We find that the microbunching instability in transport arcs has a distinguishing feature of multistage amplification (e.g, up to 6th stage for our example arcs in contrast to two stage amplification for a 3-dipole chicane). By further extending the concept of stage gain as proposed by Huang and Kim [Phys. Rev. ST Accel. Beams 5, 074401 (2002)], we developed a method to quantitatively characterize the microbunching amplification in terms of iterative or staged orders that allows the comparison of optics impacts on microbunching gain for different lattices. The parametric dependencies and Landau damping for our example lattices are also studied. Excellent agreement of the gain functions and spectra from Vlasov analysis with results from ELEGANT is achieved which helps to validate our analyses.

Poster THP022 [1.316 MB]

THP026

Design Study of LCLS Chirp-Control with a Corrugated Structure

wakefield, dipole, simulation, quadrupole

748

Z. Zhang, K.L.F. Bane, Y. Ding, Z. Huang, R.H. Iverson, T.J. Maxwell, G.V. Stupakov, L. Wang
SLAC, Menlo Park, California, USA
P. Frigola, M.A. Harrison, M. Ruelas
RadiaBeam, Santa Monica, California, USA

The purpose of this paper is to investigate the use of flat metallic plates with small corrugations as a passive dechirper, studying its effects on beam dynamics. Similar systems have been tested in Pohang and Brookhaven at relatively low energies (~100 MeV) and with relatively long bunches (>1ps) [*,**]. Four meters of such a structure are being machined by Radiabeam Systems for use in the LCLS with a high energy and femtosecond electron beam. In this paper we use a field matching program to obtain the longitudinal and transverse wakes for the purpose of the LCLS dechirper design. In addition, we fit the longitudinal wake to simple functions, so that one can obtain the wake without resorting to the field matching program. Since the transverse wakes–both dipole and quadrupole wakes–are strong, we include beam dynamics simulations to find the tolerances for injection jitter and misalignment in the LCLS.
* P. Emma, et al. PRL 112, 034801
** M. Harrison, et al., NaPAc 2013, Pasadena, USA

THP027

LCLS-II Bunch Compressor Study: 5-Bend Chicane

electron, FEL, radiation, wakefield

755

D. Khan, T.O. Raubenheimer
SLAC, Menlo Park, California, USA

In this paper, we present a potential design for a bunch compressor consisting of 5 bend magnets which is designed to compensate the transverse emittance growth due to Coherent Synchrotron Radiation (CSR). A specific implementation for the second bunch compressor in the LCLS-II is considered. The design has been optimized using the particle tracking code, ELEGANT. Comparisons of the 5-bend chicane’s performance with that of a symmetric 4-bend chicane are shown for various compression ratios and bunch charges. Additionally, a one-dimensional, longitudinal CSR model for the 5-bend design is developed and its accuracy compared against ELEGANT simulations.

Poster THP027 [0.881 MB]

THP029

MOGA OPTIMIZATION DESIGN OF LCLS-II LINAC CONFIGURATIONS

linac, undulator, 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]

THP030

Recent Photocathode R&D for the LCLS injector

laser, cathode, gun, vacuum

769

F. Zhou, A. Brachmann, W.J. Corbett, M.J. Ferreira, S. Gilevich, E.N. Jongewaard, J.R. Lewandowski, J. Sheppard, T. Vecchione, S. Vetter, S.P. Weathersby
SLAC, Menlo Park, California, USA

Funding: US DOE under contract No. DE-AC02-76SF00515
Systematic studies of the copper photocathodes identical to those used in the LCLS injector gun has been carried out at SLAC’s RF gun test facility. Recent observations at the gun test facility indicate that the pre-cleaning of the cathode prior to the installation in the gun is the major cause of the lower initial QE (~10^-6) in the RF gun. All of four cathodes tested in the gun test facility have reliable higher initial QE, 4-8·10^-5, with removal of pre-cleaning step. All of details will be described in the paper. A robust laser-assisted processing recipe has been developed. With this recipe, QE can be repeatedly evolved to about 1x10^-4 within 3-4 weeks following the laser processing, and within 1-2 days the emittance is recovered to the values as observed prior to the laser processing. When compared to previous recipe used for the present LCLS cathode, the new recipe uses lower laser fluence and provides faster emittance recovery. Laser pointing stability is a key requirement for the success of the technique. This paper presents all details of the studies for four cathodes with over a few tens of laser-assisted spots and compares the results with the present LCLS cathode.

THP031

Further Understanding the LCLS Injector Emittance

electron, collimation, laser, radiation

774

F. Zhou, K.L.F. Bane, Y. Ding, Z. Huang, H. Loos
SLAC, Menlo Park, California, USA

Funding: US DOE under contract No. DE-AC02-76SF00515
Notable COTR effect from the LCLS laser heater chicane is recently observed at the LCLS injector OTR screen, used for routine emittance measurements. The emittance with the OTR screen is under-estimated by about 30% compared to the values with the wire scanner located next to the OTR screen. The emittance with the OTR and wire scanner is compared and relevant analyses are presented. Slice emittance upstream of the LCLS BC1 is measured using a traditional transverse cavity. Recently, slice emittance downstream of the BC1 is able to be measured with a newly developed technique, using a collimator located in the middle of the BC1. The parasitic effects of using the collimator for slice emittance measurement are evaluated. The slice emittance before and after the BC1 is compared. The dependence of the slice emittance on the linearizer’s transverse offset and CSR effect from the BC1 is discussed.

THP037

Beam Performance of the Photocathode Gun for the Max IV Linac

gun, laser, cathode, injection

799

J. Andersson, F. Curbis, D. Kumbaro, F. Lindau, S. Werin
MAX-lab, Lund, Sweden

The MAX IV facility in Lund (Sweden) is under construction and conditioning of the electron guns for the injector is ongoing. There are two guns in the injector, one thermionic gun for storage ring injection and one photocathode gun for the Short Pulse Facility. In this paper we report on the beam performance tests of the photocathode gun. The measurements were performed at the MAX IV electron gun test stand during spring 2014. Parameters that were studied includes quantum efficiency, emittance and emittance compensation. Results from the measurements are also compared to particle simulations done with ASTRA.

THP039

Commissioning of the Photo-Cathode RF Gun at APS

gun, cathode, laser, solenoid

803

Y.-E. Sun, J.C. Dooling, R.R. Lindberg, A. Nassiri, S.J. Pasky, H. Shang, T.L. Smith, A. Zholents
ANL, Argonne, Ilinois, USA

A S-band RF gun is recently RF conditioned and commissioned at APS, Argonne. In this paper we report the high-power RF conditioning process of the gun. Dark currents are monitored during the RF conditioning and found to be less than 150pC. Following the RF conditioning, photo-electron beams are generated from the gun and the copper cathode quantum efficiency is monitored. We study the quantum efficiency as gun gradient varies and vacuum condition improves. Photo-electron beam enery and emittance are measured as RF gun gradient and solenoid, as well as drive-laser conditions are varied. Finally we compare our experimental results with numerical simulations.
Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.

THP041

Development of All-metal Stacked-double Gate Field Emitter Array Cathodes for X-ray Free-electron Laser Applications

electron, laser, collimation, resonance

811

S. Tsujino, H.-H. Braun, P. Das Kanungo, V. Guzenko, C. Lee, Y. Oh, M. Paraliev
PSI, Villigen PSI, Switzerland
T. Feurer
Universität Bern, Institute of Applied Physics, Bern, Switzerland

Funding: This work was partially supported by the Swiss National Science Foundation Nos. 200020₁43428 and 2000021₁47101.
We report the design, fabrication, and characterization of all-metal stacked-double-gate field emitter array (FEA) cathodes as a potential upgrade option of SwissFEL cathode at the Paul Scherrer Institute. Single-gate FEAs have demonstrated stable operation and gated field emission in pulsed diode gun with gradient up to 30 MV/m with pulse duration down to 200 ps and generation of 5 pC electron bunches by near infrared laser-induced field emission. However for high brightness applications it is crucial to reduce the beam divergence of individual beamlet by a suitable double-gate structure. The challenge lies in suppressing the concomitant decrease of the emission current when a negative focusing potential is applied to the second gate. To solve this problem, a stacked-double-gate FEAs with large collimation gate aperture diameter has been proposed. The intrinsic transverse emittance evaluated from a beam measurement for 1 mm-diameter FEA was below 0.1 mm-mrad. Compatibility with neon-gas conditioning to improve the beam uniformity and high emission current with double-gate FEAs were also demonstrated recently. The current research is focusing on the combination of the surface-plasmon-polariton resonance of the gate electrode and the near infrared laser-induced field emission to realize an ultrafast and ultrabright FEA cathode.

THP042

The LCLS-II Injector Design

gun, cathode, laser, cavity

815

J.F. Schmerge, A. Brachmann, D. Dowell, A.R. Fry, R.K. Li, Z. Li, T.O. Raubenheimer, T. Vecchione, F. Zhou
SLAC, Menlo Park, California, USA
A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
D. Filippetto, R. Huang, C. F. Papadopoulos, G.J. Portmann, J. Qiang, F. Sannibale, S.P. Virostek, R.P. Wells
LBNL, Berkeley, California, USA
A. Lunin, N. Solyak, A. Vivoli
Fermilab, Batavia, Illinois, USA

The new LCLS-II project will construct a 4 GeV continuous wave (CW) superconducting linear accelerator to simultaneously feed two undulators which will cover the spectral ranges 0.2-1.2 keV and 1-5 keV, respectively. The injector must provide up to 300 pC/bunch with a normalized emittance < 0.6 mm and peak current > 30 A at up to 1 MHz repetition rate. An electron gun with the required brightness at such high repetition rate has not yet been demonstrated. However, several different options have been explored with results that meet or exceed the performance requirements of LCLS-II. The available technologies for high repetition-rate guns, and the need to keep dark current within acceptable values, limit the accelerating gradient in the electron gun. We propose a CW normal conducting low frequency RF gun for the electron source due to a combination of the simplicity of operation and the highest achieved gradient in a CW gun, potentially allowing for lower beam emittances. The high gradient is especially significant at the 300 pC/bunch charge where beam quality can suffer due to space charge. This paper describes the design challenges and presents our solutions for the LCLS-II injector.

THP057

Longitudinal and Transverse Optimization for a High Repetition Rate Injector

gun, electron, cavity, brightness

864

C. F. Papadopoulos, D. Filippetto, R. Huang, G.J. Portmann, H.J. Qian, F. Sannibale, S.P. Virostek, R.P. Wells
LBNL, Berkeley, California, USA
A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
A. Brachmann, D. Dowell, P. Emma, Z. Li, T.O. Raubenheimer, J.F. Schmerge, T. Vecchione, F. Zhou
SLAC, Menlo Park, California, USA
A. Vivoli
Fermilab, Batavia, Illinois, USA

Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The injector is the low energy part of a linac, where space charge and kinematic effects may affect the electron beam quality significantly, and in the case of single pass systems determines the brightness in the downstream components. Following the increasing demand for high repetition rate user facilities, the VHF-gun, a normal conducting, high repetition rate (1 MHz) RF gun operating at 186 MHz has been constructed at LBNL within the APEX project and is under operation. In the current paper, we report on the status of the beam dynamics studies. For this, a multi-objected approach is used, where both the transverse and the longitudinal phase space quality is optimized, as quantified by the transverse emittance and the bunch length and energy spread respectively. We also report on different bunch charge operating modes.

THP059

The Laser Heater System of SwissFEL

laser, undulator, electron, 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)

THP064

High Repetition Rate S-band Photoinjector Design for the CLARA FEL

gun, cavity, linac, FEL

889

J.W. McKenzie, L.S. Cowie, P. Goudket, B.L. Militsyn
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
T.J. Jones
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
V.V. Paramonov
RAS/INR, Moscow, Russia

We present the design of a 1.5cell S-band photoinjector RF gun intended to be operated at repetition rates up to 400 Hz in single bunch mode. This gun is intended for use at the proposed CLARA (Compact Linear Accelerator for Research and Applications) FEL test facility at Daresbury Laboratory in the UK and will first be tested and characterised on VELA (Versatile Electron Linear Accelerator) in 2015. The final cavity design is presented including optimisation for CLARA beam dynamics, and choice of a novel coaxial H-shaped coupler.

THP073

Optics Measurements at FLASH2

optics, extraction, undulator, linac

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.

THP075

Design of TDS-based Multi-screen Electron Beam Diagnostics for the European XFEL

kicker, electron, operation, timing

909

J. Wychowaniak
TUL-DMCS, Łódź, Poland
C. Gerth, M. Yan
DESY, Hamburg, Germany

Dedicated longitudinal electron beam diagnostics is essential for successful operation of modern free-electron lasers. Demand for diagnostic data includes the longitudinal bunch profile, bunch length and slice emittance of the electron bunches. Experimental setups based on transverse deflecting structures (TDS) are excellent candidates for this purpose. At the Free-Electron Laser in Hamburg (FLASH), such a longitudinal bunch profile monitor utilizing a TDS, a fast kicker magnet and an off-axis imaging screen, has been put into operation. It enables the measurement of a single bunch out of a bunch train without affecting the remaining bunches. At the European X-ray Free-Electron Laser (XFEL) multiscreen stations in combination with TDS are planned to be installed. In order to allow for flexible measurements of longitudinal bunch profile and slice emittance, a configurable timing and trigger distribution to the fast kicker magnets and screen stations is required. In this paper, we discuss various operation patterns and the corresponding realization based on MTCA.4 technology.

THP088

Comparison of Quadrupole Scan and Multi-screen Method for the Measurement of Projected and Slice Emittance at the SwissFEL Injector Test Facility

quadrupole, diagnostics, optics, FEL

941

M. Yan, B. Beutner, C. Gerth
DESY, Hamburg, Germany
R. Ischebeck, E. Prat
PSI, Villigen PSI, Switzerland

High-brightness electron bunches with small transverse emittance are required to drive X-ray free-electron lasers (FELs). For the measurement of the transverse emittance, the quadrupole scan and multi-screen methods are the two most common procedures. By employing a transverse deflecting structure, the measurement of the slice emittance becomes feasible. The quadrupole scan is more flexible in freely choosing the data points during the scan, while the multi-screen method allows on-line emittance measurements utilising off-axis screens in combination with fast kicker magnets. The latter is especially the case for high-repetition multi-bunch FELs, such as the European XFEL, which offer the possibility of on-line diagnostics. In this paper, we present comparative measurements of projected and slice emittance applying these two methods at the SwissFEL Injector Test Facility and discuss the implementation of on-line diagnostics at the European XFEL.

THC02

Thermal Emittance Measurements at the SwissFEL Injector Test Facility

cathode, laser, gun, electron

970

E. Prat, S. Bettoni, H.-H. Braun, M.C. Divall, R. Ganter, C.P. Hauri, T. Schietinger, A. Trisorio, C. Vicario
PSI, Villigen PSI, Switzerland
C.P. Hauri
EPFL, Lausanne, Switzerland

In a laser-driven RF-gun the ultimate limit of the beam emittance is the transverse momentum of the electrons as they exit the cathode, the so-called intrinsic or thermal emittance. In this contribution we present measurements of the thermal emittance at the SwissFEL Injector Test Facility for electron beam charges down to a few tens of fC. We have studied the thermal emittance and QE dependence on the laser wavelength, the RF-gun gradient and the cathode material (Cu and Cs2Te).

Slides THC02 [1.063 MB]

THC03

Suppression of the CSR-induced Emittance Growth in Achromats using Two-dimensional point-kick Analysis

dipole, simulation, optics, linear-collider

976

Y. Jiao, X. Cui, X.Y. Huang, G. Xu
IHEP, Beijing, People's Republic of China

Coherent synchrotron radiation (CSR) effect causes transverse emittance dilution in high-brightness light sources and linear colliders. Suppression of the emittance growth induced by CSR is essential and critical to preserve the beam quality and to help improve the machine performance. To evaluate the CSR effect analytically, we propose a novel method, named “two-dimensional point-kick analysis”. In this method, the CSR-induced emittance growth in an n-dipole achromat can be evaluated with the analysis of only the motion of particle in (x, x') two-dimensional plane with n-point kicks, which can be, to a large extent, counted separately. To demonstrate the effectiveness of this method, the CSR effect in a two-diople achromat and a symmetric TBA is studied, and generic conditions of suppressing the CSR-induced emittance growth, which are independent of concrete element parameters and are robust against the variation of initial beam distribution, are found. These conditions are verified with the ELEGANT simulations and can be rather easily applied to real machines.

Slides THC03 [1.941 MB]

THC04

Beam Simulations of High Brightness Photocathode DC Gun and Injector for High Repetition FEL Light Source

gun, operation, FEL, cathode

980

T. Miyajima, Y. Honda, X. Jin, T. Uchiyama, M. Yamamoto
KEK, Ibaraki, Japan
R. Hajima, R. Nagai, N. Nishimori
JAEA, Ibaraki-ken, Japan

As a next generation FEL light source based on linac, high repetition rate operation to increase average FEL power has been proposed, e.g. LCLS-II project. The injector, which generates high brightness and high average current beam, is one of key components. A photocathode DC gun and superconducting RF cavities, which are developed for ERL light source, can be employed for the high repetition rate injector. For high repetition rate operation of FEL light source, injector simulations were carried out based on ERL injector with demonstrated hardware performance by the cERL beam operation in KEK. The optimization results show that the gun voltage of 500 kV is helpful to achieve low emittance. In addition, to estimate optimum gun voltage and cavity acceleration gradient for the FEL operation, two optimizations with different injector layouts were carried out. The results show that the both different layouts have potential to achieve target emittance for FEL operation. Under the realistic operation condition, the transverse normalized rms emittance of 0.8 mm mrad with the rms bunch length of 3 ps, the bunch charge of 325 pC, and the beam energy of 10 MeV is obtained from the optimizations.

Slides THC04 [3.796 MB]

FRB02

A Collinear Wakefield Accelerator for a High Repetition Rate Multi-beamline Soft X-ray FEL Facility

wakefield, electron, FEL, acceleration

993

A. Zholents, W. Gai, R.R. Lindberg, J.G. Power, Y.-E. Sun
ANL, Argonne, Ilinois, USA
C.-J. Jing, A. Kanareykin
Euclid TechLabs, LLC, Solon, Ohio, USA
C. Li, C.-X. Tang
TUB, Beijing, People's Republic of China
D.Y. Shchegolkov, E.I. Simakov
LANL, Los Alamos, New Mexico, USA

Funding: Supported by U.S. Department of Energy under Contract No. DE-AC02-06CH11357 and by the U.S. Department of Energy Laboratory LDRD program at Los Alamos National Laboratory.
A concept is presented for a multi beamline soft x-ray free-electron laser (FEL) facility where several FEL undulator lines are driven by an equal number of high repetition rate single-stage collinear wakefield accelerators (CWA). A practical design of the CWA, extending over 30 meters and embedded into a quadrupole wiggler, is considered. The wiggler’s structure of alternating focusing and defocusing quadrupoles is used to control single-bunch breakup instability. It is shown that practical restrictions on the maximum attainable quadrupole field limit the maximum attainable charge in the drive bunch whose sole purpose is to produce a high accelerating field in the CWA for the following main bunch. It is also pointed out that the distance between drive and main bunches varies along the accelerator, causing a measurable impact on the energy gain by the main bunch and on the energy spread of electrons in it. Means to mitigate these effects are proposed and results are presented for numerical simulations demonstrating the main bunch with plausible parameters for FEL application including a relatively small energy spread. Finally, results are presented for the expected FEL performance using an appropriately chosen undulator.

Slides FRB02 [6.512 MB]

FRB04

Divergence Reduction and Emittance Conservation in a Laser Plasma Acceleration Stage

plasma, laser, acceleration, extraction

999

A.R. Maier, I. Dornmair
CFEL, Hamburg, Germany
K. Flöttmann
DESY, Hamburg, Germany

Plasma accelerators promise a compact source of highly relativistic electron beams. Driven by high-intensity lasers or high-energetic electron beams, the longitudinal and transverse electric fields inside the plasma cavitiy support the generation of GeV electron beams over m-scale distances, while measured emittances on the order of 0.1 mm.mrad have been reported from plasma-driven accelerators. However, it remains challenging to conserve this excellent emittance when coupling from the plasma into vacuum and a subsequent beam optics, especially when considering the large energy spread, typically accumulated during the off-crest acceleration inside the plasma. Recently, we presented an analytical solution [1] to describe an adiabatic matching from the plasma into vacuum. Further elaborating this concept [2], we will discuss the generation of low-divergence electron beams from a tailored plasma target in order to preserve the emittance generated within the plasma. We will apply our concept to an externally injected electron bunch, that is matched in and out of a tailored plasma target, generating a GeV-level electron beam with low divergence and good emittance.
* K. Floettmann, Phys. Rev. ST - Accel. Beams 17, 054402 (2014)
** I. Dornmair, K. Floettmann, and A. R. Maier, submitted (2014)