FEL2014 - List of Keywords (operation)

Paper	Title	Other Keywords	Page
MOA03	First Lasing at FLASH2	undulator, electron, 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]

MOP007	High Accuracy Shimming Technique for the Phase Shifters of the European XFEL	undulator, 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	undulator, controls, 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.

MOP019	Double-grating Monochromator for Ultrafast Free-electron Laser Beamlines	FEL, laser, radiation, focusing	58
	F. Frassetto, L. P. Poletto CNR-IFN, Padova, Italy M. Kuhlmann, E. Plönjes DESY, Hamburg, Germany
	We present the design of an ultrafast monochromator explicitly designed for extreme-ultraviolet FEL sources, in particular the upcoming FLASH II at DESY. The design originates from the variable-line-spaced (VLS) grating monochromator by adding a second grating to compensate for the pulse-front tilt given by the first grating after the diffraction. The covered spectral range is 6-60 nm, the spectral resolution is in the range 1000–2000, while the residual temporal broadening is lower than 15 fs. The proposed design minimizes the number of optical elements, since just one grating is added with respect to a standard VLS monochromator and requires simple mechanical movements, since only rotations are needed to perform the spectral scan.

MOP022	Pulse by Pulse Electron Beam Distribution for Multi-beamline Operation at SACLA	electron, kicker, septum, linac	71
	T. Hara, T. Inagaki, C. Kondo, Y. Otake, H. Takebe, H. Tanaka RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan K. Fukami JASRI/SPring-8, Hyogo-ken, Japan
	In order to meet the increasing demand for XFEL user operation, the second undulator beamline (BL2) will be installed during the 2014 summer shutdown at SACLA. Following the installation of BL2, a pulse by pulse electron beam distribution system composed of a kicker and a DC twin-septum magnet, which are currently under development, is planned be installed in January 2015. To distribute the electron beam on a bunch-to-bunch basis, the electron beam is deflected into 0 and ±10 mrad directions at 60 Hz by the kicker, and then the DC twin-septum magnet augments the separation angle to ±50 mrad. The kicker magnet is driven by a 60 Hz trapezoidal waveform and stability less than 30 ppm (peak-peak) has been achieved. This pulse by pulse distribution system will be also used for the beam injection to the upgraded low emittance ring of SPring-8 (SPring-8-II) in future. Since the SPring-8-II storage ring has a small dynamic aperture, low emittance is required for the injection beam. Also the beam injection in parallel with the XFEL operation enables to save the running cost of the injector during top-up operation.

MOP039	High Stability Resonant Kicker Development for the SwissFEL Switch Yard	kicker, dipole, electron, linac	103
	M. Paraliev, H.-H. Braun, S. Dordevic, C.H. Gough PSI, Villigen PSI, Switzerland
	The SwissFEL is a linac-based X-ray free electron laser facility under construction at the Paul Scherrer Institute. The facility will provide femtosecond, high brightness X-ray pulses for fundamental and applied science research. To increase facility efficiency, a double bunch operation is planned to serve simultaneously two experimental stations at the full linac repetition rate. The main linac will accelerate two electron bunches spaced 28 ns apart and a fast and stable deflecting system will be used to separate the two bunches into two different undulator lines. The deflecting system uses a novel concept based on resonant kicker magnets. A prototype kicker magnet and its control system were designed and built. Since stability is crucial, the stability performance of the prototype was studied. The peak to peak amplitude stability of ±11 ppm (3.5 ppm rms) was achieved, which is well within the FEL tolerance of ±80 ppm. The layout of the deflecting system and the key design parameters are also presented.

MOP043	Magnetic Design of an Apple III Undulator for SwissFEL	undulator, vacuum, polarization, 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.

MOP046	Undulator Radiation Damage Experience at LCLS	undulator, radiation, electron, 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.

MOP059	Beam Dynamic Simulations for Single Spike Radiation with Short-Pulse Injector Laser at FLASH	laser, simulation, electron, radiation	173
	M. Rehders University of Hamburg, Hamburg, Germany J. Rönsch-Schulenburg CFEL, Hamburg, Germany J. Rönsch-Schulenburg, J. Roßbach Uni HH, Hamburg, Germany S. Schreiber DESY, Hamburg, Germany
	Funding: The project has been supported by the Federal Ministry of Education and Research of Germany (BMBF) under contract No. 05K10GU2 and FSP301 This paper discusses the generation of single spike SASE pulses at soft x-ray wavelength at the free-electron laser FLASH by using very short electron bunches of only a few micrometer bunch length. In order to achieve these extremely short bunch lengths, very low bunch charges (in the order of 20 pC) and short electron bunches exiting the photo-injector are required. For this, a new short-pulse injector laser with adjustable rms pulse duration in the range of 0.7 ps to 1.6 ps and bunch charges up to 200 pC was installed, extending the electron beam parameter range before bunch compression in magnetic chicanes. Beam dynamic studies have been performed to optimize the injection and compression of low-charge electron bunches by controlling the effect of coherent synchrotron radiation and space-charge induced bunch lengthening and emittance growth. Optimization includes the pulse parameters of the injector laser. The simulation codes ASTRA, CSRtrack and Genesis 1.3 were employed.

MOP063	A Novel Modeling Approach for Electron Beams in SASE FELs	radiation, FEL, target, electron	190
	P. Niknejadi, J. Madey University of Hawaii, Honolulu,, USA
	We have recently shown that the Wheeler-Feynman analysis of the interaction of a moving charge with distant absorbers [] provides a perfect match to the energy radiated by two coherently oscillating charged particles (a heretofore unsolved problem in classical electrodynamics) []. Here we explain the need to include the Wheeler-Feynman coherent radiation reaction force as an integral part of the solution of the boundary value problem of free electron lasers (FELs) that radiate into “free space”. We will also discuss how the advanced field of the absorber can interact with the radiating particles at the time of emission. Finally we will introduce and explore the possibility of improving the temporal coherence in the self amplified spontaneous emission (SASE) FELs as well as the possibility of optimizing the spectrum of the emitted coherent radiation by SASE FELs via altering the structure of their targets by including the Wheeler-Feynman coherent radiation reaction force in the analysis of FEL operations. Wheeler, J. A.; Feynman, R. P, Rev. Mod. Phys. 17, 157, 1945. ** P. Niknejadi et al. "Energy Conservation of Coherently Oscillating Charged Particles in Classical Electrodynamics" submitted.

MOP066	An Overview of the Radiation Properties of the European XFEL	electron, radiation, undulator, 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, undulator, 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.

MOP077	Measurements of the FEL-bandwidth Scaling with Harmonic Number in a HGHG FEL	FEL, laser, electron, experiment	227
	E. Allaria, M.B. Danailov, W.M. Fawley, E. Ferrari, L. Giannessi Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy E. Ferrari Università degli Studi di Trieste, Trieste, Italy L. Giannessi ENEA C.R. Frascati, Frascati (Roma), Italy
	In this work we report recent measurements done at FERMI showing the dependence of the FEL bandwidth with respect to the seed laser harmonic at which the FEL is operated. Comparison of FEL spectra for different Fourier-limit seed and chirp pulses is also reported.

TUA02	A Review of High Power OPCPA Technology for High Repetition Rate Free-Electron Lasers	laser, FEL, electron, free-electron-laser	310
	M.J. Prandolini, R. Riedel HIJ, Jena, Germany M. Schulz DESY, Hamburg, Germany F. Tavella SLAC, Menlo Park, California, USA
	High repetition rate free-electron lasers (FEL) require the development of new laser systems that have the ability to operate at high average power. Optical parametric chirped-pulse amplification (OPCPA) is presently the most promising method to fulfill these requirements. This technique has been used to demonstrate amplification up to tens of watts with a repetition rate in the range between tens of kHz to MHz in burst and continuous mode. We review the current OPCPA technology for systems operating around 800 nm; this includes various frontend options, pump amplifier technology and latests results, and we discuss the important requirements for achieving high power lasers in both burst and continuous operation. Work supported by the Helmholtz Institute Jena and the Deutsches Elektronen-Synchrotron DESY in Hamburg.
	Slides TUA02 [4.997 MB]

TUB04	Operation of FLASH with Short SASE-FEL Radiation Pulses	laser, FEL, electron, free-electron-laser	342
	J. Rönsch-Schulenburg, E. Hass, N.M. Lockmann, T. Plath, M. Rehders, J. Roßbach Uni HH, Hamburg, Germany G. Brenner, S. Dziarzhytski, T. Golz, H. Schlarb, B. Schmidt, E. Schneidmiller, S. Schreiber, B. Steffen, N. Stojanovic, S. Wunderlich, M.V. Yurkov DESY, Hamburg, Germany
	Funding: The project has been supported by the Federal Ministry of Education and Research of Germany (BMBF) under contract No. 05K10GU2 and FSP301 This paper describes the experimental activity on the generation of very short FEL pulses in the soft x-ray range in the SASE-mode at the high-gain free-electron laser FLASH [1, 2]. The key element, a photo-injector laser which is able to generate laser pulses of about 2 ps FWHM has been optimized and commissioned. It allows the generation of shorter bunches with low bunch charge (of up to 200 pC) directly at the photo-cathode. Initially shorter injector laser pulses and thus shorter bunches eases the required bunch compression factor for short pulses below 10 fs duration which makes operation of the electron beam formation system to be more robust with respect to jitters and collective effects. As a result, overall stability of SASE FEL performance is improved. In the optimal case single-spike operation can be achieved. In this paper the experimental results on production of short electron bunches and the SASE performance using the new injector laser will be shown and the measured electron bunch and FEL radiation properties are discussed. In addition, optimizations of bunch diagnostics for low charge and short bunches are discussed.
	Slides TUB04 [1.201 MB]

TUP069	Cavity Length Change vs. Mirror Steering in a Ring Confocal Resonator	cavity, wiggler, FEL, optics	516
	S.V. Benson JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-84-ER40150, the Office of Naval Research, and the Joint Technology Office. In principle, a ring confocal resonator allows for the use of a short Rayleigh length without the extreme sensi-tivity to mirror steering typical in a near-concentric reso-nator [1]. One possible weakness of such a resonator is that the cavity length is no longer independent of the mirror steering. This is one of the strengths of a linear resonator. In this presentation, it is shown that, in a simple 2-dimensional corner cube type ring confocal resonator, the cavity length is, in fact, not dependent on the mirror steering to first order in the mirror angles. Thus the ring-confocal resonator might be a very easy-to-operate and stable resonator for short Rayleigh range operation in FEL oscillators [1] Stephen Benson, George Neil, Michelle Shinn, Laser and Beam Control Technologies, Santanu Basu, James Riker, Editors, Proceedings of SPIE Vol. 4632 (2002).

TUP073	High Power Operation of the THz FEL at ISIR, Osaka University	FEL, electron, linac, gun	528
	K. Kawase, M. Fujimoto, S. Funakoshi, K. Furukawa, A. Irizawa, G. Isoyama, R. Kato, K. Kubo, K. Miyazaki, S. Suemine, A. Tokuchi, R. Tsutsumi, M. Yaguchi ISIR, Osaka, Japan
	The THz FEL at Osaka University is based on the L-band linac that provides a multi-bunch electron beam with an 8 us duration in the energy range from 12.5 to 20 MeV. Although the RF frequency of the linac is 1.3 GHz, the bunch intervals are expanded to 9.2 ns for the FEL using a sub-harmonic buncher system that operates at 10⁸ MHz, to enhance the bunch charge to 1 nC/bunch. The FEL covers the wavelength range from 30 to 150 um, and maximum energies of the macropulse and the micropulse are 3.7 mJ and 11 uJ, respectively, at ~70 um measured at an experimental station. To enhance the FEL power further, the electron beam current cannot be increased simply because the beam loading in the acceleration tube is too high. To solve this problem, we have developed a 27 MHz grid pulser for the thermionic electron gun that makes the bunch intervals 4 times longer and increases charge of the bunch 4 times higher whereas the beam loading is the same as that in the 108 MHz mode. In this new operation mode, where a single FEL pulse lases in the cavity, we have succeeded in obtaining the micropulse energy exceeding 100 uJ at a wavelength of 68 um.

TUP085	FERMI Status Report	FEL, electron, experiment, laser	564
	M. Svandrlik, E. Allaria, F. Bencivenga, C. Callegari, F. Capotondi, D. Castronovo, P. Cinquegrana, M. Coreno, R. Cucini, I. Cudin, G. D'Auria, M.B. Danailov, R. De Monte, G. De Ninno, P. Delgiusto, A.A. Demidovich, S. Di Mitri, B. Diviacco, A. Fabris, R. Fabris, W.M. Fawley, M. Ferianis, E. Ferrari, P. Finetti, L. Fröhlich, P. Furlan Radivo, G. Gaio, D. Gauthier, F. Gelmetti, L. Giannessi, M. Kiskinova, S. Krecic, M. Lonza, N. Mahne, C. Masciovecchio, M. Milloch, F. Parmigiani, G. Penco, L. Pivetta, O. Plekan, M. Predonzani, E. Principi, L. Raimondi, P. Rebernik Ribič, F. Rossi, L. Rumiz, C. Scafuri, C. Serpico, P. Sigalotti, C. Spezzani, C. Svetina, M. Trovò, A. Vascotto, M. Veronese, R. Visintini, D. Zangrando, M. Zangrando Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
	FERMI, the seeded FEL located at the Elettra laboratory in Trieste, Italy, is now in regular operation for users with its first FEL line, FEL-1, which covers the wavelength range between 100 and 20 nm. We will give an overview of the typical operating modes of the facility for users and we will report on the status of beamlines and experimental stations. Three beamlines are now opened for users, three more are in construction. Meanwhile, the second FEL line of FERMI, FEL-2, a HGHG double stage cascade covering the wavelength range 20 to 4 nm is still under commissioning; we will report on the latest results in particular at the shortest wavelength, 4 nm in the fundamental.

TUP087	The Status of LUNEX5 Project	electron, FEL, laser, undulator	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.

WEB05	FLASH: First Soft X-ray FEL Operating Two Undulator Beamlines Simultaneously	electron, laser, undulator, 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]

THP002	Beam Energy Management and RF Failure Compensation Scenarios for the European XFEL	linac, klystron, optics, quadrupole	672
	B. Beutner DESY, Hamburg, Germany
	The operation of complex systems as the driver linacs for free-electron-lasers is limited by the reliability of the individual components. Failures of RF systems can therefore constrict FEL availability. Typically reserves are included in the overall linac voltage capacity to allow for redistribution of acceleration in case of an RF failure. However, such redistributions of the acceleration of the linac affects the beam dynamics of the machine. While the effects on the optics can easily be compensated by rescaling of the quadrupole magnet strength, the bunch compression set-up requires a more involved investigation. In this paper we discuss studies for an energy management system for the European XFEL.

THP003	Two Charges in the Same Bunch Train at the European XFEL	simulation, laser, emittance, 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

THP046	Cu and Cs2Te Cathodes Preparation and QE History at the SwissFEL Injector Test Facility.	cathode, laser, gun, vacuum	832
	J. Bossert, R. Ganter, M. Schaer, T. Schietinger PSI, Villigen PSI, Switzerland
	The installation of a load-lock chamber attached to the SwissFEL gun gives the possibility to carefully prepare the metallic cathodes under vacuum and also to use semiconductor cathodes like Cs2Te cathodes which cannot be transported through air. The paper presents the preparation procedures used for copper (QE>1.e-4) and Cs2Te cathodes (based on a CERN recipe) together with surface analysis results (SEM, EDX, interferometry, microscopy). Finally, the QE evolutions obtained in the SwissFEL Injector test facility as well as in a test stand are discussed for both materials.

THP051	Thyratron Replacement	klystron, network, target, linear-collider	847
	I. Roth, M.P.J. Gaudreau, M.K. Kempkes Diversified Technologies, Inc., Bedford, Massachusetts, USA
	Funding: DOE Contract DE-SC0011292 Semiconductor thyristers have long been used as a replacement for thyratrons, at least in low power or long pulse RF systems. To date, however, such thyristor assemblies have not demonstrated the reliability needed for installation in short pulse, high peak power RF stations used with many pulsed electron accelerators. The difficulty is that a fast rising current in a thyristor tends to be carried in a small region, rather than across the whole device, and this localized current concentration can cause a short circuit failure. It is not clear that this failure mode can be overcome with currently available device designs. An alternate solid-state device, the insulated-gate bipolar transistor (IGBT), can readily operate at the speed needed for the accelerator, but commercial IGBTs cannot handle the voltage and current required. Diversified Technologies, Inc. (DTI) has patented and refined the technology required to build these arrays of series-parallel connected switches. Under DOE contract, DTI is currently developing an affordable, reliable, form-fit-function replacement for the klystron modulator thyratrons at SLAC capable of pulsing at 360 kV, 420 A, 6 μs, and 120 Hz.

THP058	Solid-State Switch for a Klystron Modulator for Stable Operation of a THz- FEL	FEL, klystron, electron, linac	868
	G. Isoyama, M. Fujimoto, S. Funakoshi, K. Furukawa, A. Irizawa, R. Kato, K. Kawase, K. Miyazaki, A. Tokuchi, R. Tsutsumi, M. Yaguchi ISIR, Osaka, Japan F. Kamitsukasa Osaka University, Graduate School of Science, Osaka, Japan
	We have been conducting studies on upgrade of the THz-FEL and its applications, using the L-band electron linac at ISIR, Osaka University. The stability of the FEL is crucial for these studies and the operation of the FEL depends on characteristics of the electron beam, especially on stability of the electron energy, which is strongly affected by the RF power and its phase provided to the linac. We uses a klystron modulator with the a highly stable charging system to the PFN with a fractional variation of 8×10^-5 (peak-to-peak), but the klystron voltage varies by one order of magnitude larger due probably to the thyratron used as a high voltage and high current switch in the klystron modulator. In order to make the stability of the FEL higher, we have developed a solid-state switch using static induction thyristors. The performance of the switch is as follows; the maximum holding voltage is 25 kV, the maximum current is 6 kA for the pulse duration of 10 us, the switching time is 270 ns, and the maximum repetition frequency is 10 Hz. The intensity fluctuation of the FEL macropulse is reduced to a few percents using the solid state switch.

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

THP063	Production of C-band Disk-loaded type CG Accelerating Structures	vacuum, cavity, resonance, acceleration	885
	N. Shigeoka, S. Miura, D. Suzuki MHI, Hiroshima, Japan T. Asaka, T. Inagaki, Y. Otake, T. Sakurai RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan H. Ego JASRI/SPring-8, Hyogo-ken, Japan
	In April 2013, MITSUBISHI HEAVY INDUSTRIES, LTD. contracted with RIKEN to produce six C-band disk-loaded type and constant gradient (CG) accelerating structures for removal of SCSS. These structures were newly designed by RIKEN for operation with an acceleration gradient of over 45 MeV/m and a repletion rate of 120 pps. The first structure was delivered in August 2013 to RIKEN and the other five was also delivered in March 2014. The accelerating structures were stacked from one hundred accelerating cells and formed by the vacuum brazing method. These cells using oxygen free copper were ultra-precisely machined. Unlike the C-band choke-mode type structures, which MHI manufactured in past for SACLA, the accelerating cells of the CG structure can be tuned after the brazing by pushing dimpling at the tuning hole of each cell. Demands of a VSWR < 1.1 and a phase error < 3 degree are fulfilled after the tuning by using the nodal shift method, which corrects cell frequency shifts due to the machining errors of cells and a cell’s deformation by the heat cycle of the brazing. The detailed results of the production and low-power RF tests will be presented in this presentation.
	Poster THP063 [0.623 MB]

THP069	Performance Study of High Bandwidth Pickups Installed at FLASH and ELBE for Femtosecond-Precision Arrival Time Monitors	pick-up, laser, electron, experiment	893
	M.K. Czwalinna, C. Gerth, H. Schlarb, C. Sydlo DESY, Hamburg, Germany A. Angelovski, R. Jakoby, A. Penirschke TU Darmstadt, Darmstadt, Germany M. Gensch, M. Kuntzsch HZDR, Dresden, Germany M. Kuntzsch TU Dresden, Dresden, Germany T. Weiland TEMF, TU Darmstadt, Darmstadt, Germany
	At today's free-electron lasers, high-resolution electron bunch arrival time measurements have become increasingly more important in fast feedback systems for a timing jitter reduction down to the femtosecond level as well as for time-resolved pump-probe experiments. This is fulfilled by arrival time monitors which employ an electro-optical detection scheme by means of synchronised ultrashort laser pulses. Even more, at FLASH and the European XFEL the measurement has to cover a wide range of bunch charges from 1 nC down to 20 pC with equally sub-10 fs resolution. To meet these requirements, recently a high bandwidth pickup electrode with a cut-off frequency above 40 GHz has been developed. These pickups are installed at the macro-pulsed SRF accelerator of the free-electron laser FLASH and at the macro-pulsed continuous wave SRF accelerator ELBE. In this paper we present an evaluation of the pickup performance by direct signal measurements with high bandwidth oscilloscopes and by use of the electro-optical arrival time monitor.

THP075	Design of TDS-based Multi-screen Electron Beam Diagnostics for the European XFEL	kicker, emittance, electron, 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.

THP090	Femtosecond Timing Distribution for the European XFEL	laser, timing, status, FEL	945
	C. Sydlo, M.K. Czwalinna, M. Felber, C. Gerth, T. Lamb, H. Schlarb, S. Schulz, F. Zummack DESY, Hamburg, Germany S. Jabłoński Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
	Accurate timing synchronization on the femtosecond timescale is an essential installation for time-resolved experiments at free-electron lasers (FELs) such as FLASH and the upcoming European XFEL. To date the required precision levels can only be achieved by a laser-based synchronization system. Such a system has been successfully deployed at FLASH and is based on the distribution of femtosecond laser pulses over actively stabilized optical fibers. Albeit its maturity and proven performance this system had to undergo a major redesign for the upcoming European XFEL due to the enlarged number of stabilized optical fibers and an increase by a factor of up to 10 in length. The experience and knowledge gathered from the operation of the optical synchronization system at FLASH has led to an elaborate and modular precision instrument which can stabilize polarization maintaining fibers for highest accuracy as well as economic single mode fibers for shorter lengths. This paper reports on the laser-based synchronization system focusing on the active fiber stabilization units for the European XFEL, discusses major complications, their solutions and and the most recent performance results.

THC04	Beam Simulations of High Brightness Photocathode DC Gun and Injector for High Repetition FEL Light Source	gun, emittance, 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]

Paper

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MOA03

First Lasing at FLASH2

undulator, electron, 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]

MOP007

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

undulator, 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

undulator, controls, 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.

MOP019

Double-grating Monochromator for Ultrafast Free-electron Laser Beamlines

FEL, laser, radiation, focusing

58

F. Frassetto, L. P. Poletto
CNR-IFN, Padova, Italy
M. Kuhlmann, E. Plönjes
DESY, Hamburg, Germany

We present the design of an ultrafast monochromator explicitly designed for extreme-ultraviolet FEL sources, in particular the upcoming FLASH II at DESY. The design originates from the variable-line-spaced (VLS) grating monochromator by adding a second grating to compensate for the pulse-front tilt given by the first grating after the diffraction. The covered spectral range is 6-60 nm, the spectral resolution is in the range 1000–2000, while the residual temporal broadening is lower than 15 fs. The proposed design minimizes the number of optical elements, since just one grating is added with respect to a standard VLS monochromator and requires simple mechanical movements, since only rotations are needed to perform the spectral scan.

MOP022

Pulse by Pulse Electron Beam Distribution for Multi-beamline Operation at SACLA

electron, kicker, septum, linac

71

T. Hara, T. Inagaki, C. Kondo, Y. Otake, H. Takebe, H. Tanaka
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
K. Fukami
JASRI/SPring-8, Hyogo-ken, Japan

In order to meet the increasing demand for XFEL user operation, the second undulator beamline (BL2) will be installed during the 2014 summer shutdown at SACLA. Following the installation of BL2, a pulse by pulse electron beam distribution system composed of a kicker and a DC twin-septum magnet, which are currently under development, is planned be installed in January 2015. To distribute the electron beam on a bunch-to-bunch basis, the electron beam is deflected into 0 and ±10 mrad directions at 60 Hz by the kicker, and then the DC twin-septum magnet augments the separation angle to ±50 mrad. The kicker magnet is driven by a 60 Hz trapezoidal waveform and stability less than 30 ppm (peak-peak) has been achieved. This pulse by pulse distribution system will be also used for the beam injection to the upgraded low emittance ring of SPring-8 (SPring-8-II) in future. Since the SPring-8-II storage ring has a small dynamic aperture, low emittance is required for the injection beam. Also the beam injection in parallel with the XFEL operation enables to save the running cost of the injector during top-up operation.

MOP039

High Stability Resonant Kicker Development for the SwissFEL Switch Yard

kicker, dipole, electron, linac

103

M. Paraliev, H.-H. Braun, S. Dordevic, C.H. Gough
PSI, Villigen PSI, Switzerland

The SwissFEL is a linac-based X-ray free electron laser facility under construction at the Paul Scherrer Institute. The facility will provide femtosecond, high brightness X-ray pulses for fundamental and applied science research. To increase facility efficiency, a double bunch operation is planned to serve simultaneously two experimental stations at the full linac repetition rate. The main linac will accelerate two electron bunches spaced 28 ns apart and a fast and stable deflecting system will be used to separate the two bunches into two different undulator lines. The deflecting system uses a novel concept based on resonant kicker magnets. A prototype kicker magnet and its control system were designed and built. Since stability is crucial, the stability performance of the prototype was studied. The peak to peak amplitude stability of ±11 ppm (3.5 ppm rms) was achieved, which is well within the FEL tolerance of ±80 ppm. The layout of the deflecting system and the key design parameters are also presented.

MOP043

Magnetic Design of an Apple III Undulator for SwissFEL

undulator, vacuum, polarization, 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.

MOP046

Undulator Radiation Damage Experience at LCLS

undulator, radiation, electron, 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.

MOP059

Beam Dynamic Simulations for Single Spike Radiation with Short-Pulse Injector Laser at FLASH

laser, simulation, electron, radiation

173

M. Rehders
University of Hamburg, Hamburg, Germany
J. Rönsch-Schulenburg
CFEL, Hamburg, Germany
J. Rönsch-Schulenburg, J. Roßbach
Uni HH, Hamburg, Germany
S. Schreiber
DESY, Hamburg, Germany

Funding: The project has been supported by the Federal Ministry of Education and Research of Germany (BMBF) under contract No. 05K10GU2 and FSP301
This paper discusses the generation of single spike SASE pulses at soft x-ray wavelength at the free-electron laser FLASH by using very short electron bunches of only a few micrometer bunch length. In order to achieve these extremely short bunch lengths, very low bunch charges (in the order of 20 pC) and short electron bunches exiting the photo-injector are required. For this, a new short-pulse injector laser with adjustable rms pulse duration in the range of 0.7 ps to 1.6 ps and bunch charges up to 200 pC was installed, extending the electron beam parameter range before bunch compression in magnetic chicanes. Beam dynamic studies have been performed to optimize the injection and compression of low-charge electron bunches by controlling the effect of coherent synchrotron radiation and space-charge induced bunch lengthening and emittance growth. Optimization includes the pulse parameters of the injector laser. The simulation codes ASTRA, CSRtrack and Genesis 1.3 were employed.

MOP063

A Novel Modeling Approach for Electron Beams in SASE FELs

radiation, FEL, target, electron

190

P. Niknejadi, J. Madey
University of Hawaii, Honolulu,, USA

We have recently shown that the Wheeler-Feynman analysis of the interaction of a moving charge with distant absorbers [*] provides a perfect match to the energy radiated by two coherently oscillating charged particles (a heretofore unsolved problem in classical electrodynamics) [**]. Here we explain the need to include the Wheeler-Feynman coherent radiation reaction force as an integral part of the solution of the boundary value problem of free electron lasers (FELs) that radiate into “free space”. We will also discuss how the advanced field of the absorber can interact with the radiating particles at the time of emission. Finally we will introduce and explore the possibility of improving the temporal coherence in the self amplified spontaneous emission (SASE) FELs as well as the possibility of optimizing the spectrum of the emitted coherent radiation by SASE FELs via altering the structure of their targets by including the Wheeler-Feynman coherent radiation reaction force in the analysis of FEL operations.
* Wheeler, J. A.; Feynman, R. P, Rev. Mod. Phys. 17, 157, 1945.
** P. Niknejadi et al. "Energy Conservation of Coherently Oscillating Charged Particles in Classical Electrodynamics" submitted.

MOP066

An Overview of the Radiation Properties of the European XFEL

electron, radiation, undulator, 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, undulator, 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.

MOP077

Measurements of the FEL-bandwidth Scaling with Harmonic Number in a HGHG FEL

FEL, laser, electron, experiment

227

E. Allaria, M.B. Danailov, W.M. Fawley, E. Ferrari, L. Giannessi
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
E. Ferrari
Università degli Studi di Trieste, Trieste, Italy
L. Giannessi
ENEA C.R. Frascati, Frascati (Roma), Italy

In this work we report recent measurements done at FERMI showing the dependence of the FEL bandwidth with respect to the seed laser harmonic at which the FEL is operated. Comparison of FEL spectra for different Fourier-limit seed and chirp pulses is also reported.

TUA02

A Review of High Power OPCPA Technology for High Repetition Rate Free-Electron Lasers

laser, FEL, electron, free-electron-laser

310

M.J. Prandolini, R. Riedel
HIJ, Jena, Germany
M. Schulz
DESY, Hamburg, Germany
F. Tavella
SLAC, Menlo Park, California, USA

High repetition rate free-electron lasers (FEL) require the development of new laser systems that have the ability to operate at high average power. Optical parametric chirped-pulse amplification (OPCPA) is presently the most promising method to fulfill these requirements. This technique has been used to demonstrate amplification up to tens of watts with a repetition rate in the range between tens of kHz to MHz in burst and continuous mode. We review the current OPCPA technology for systems operating around 800 nm; this includes various frontend options, pump amplifier technology and latests results, and we discuss the important requirements for achieving high power lasers in both burst and continuous operation.
Work supported by the Helmholtz Institute Jena and the Deutsches Elektronen-Synchrotron DESY in Hamburg.

Slides TUA02 [4.997 MB]

TUB04

Operation of FLASH with Short SASE-FEL Radiation Pulses

laser, FEL, electron, free-electron-laser

342

J. Rönsch-Schulenburg, E. Hass, N.M. Lockmann, T. Plath, M. Rehders, J. Roßbach
Uni HH, Hamburg, Germany
G. Brenner, S. Dziarzhytski, T. Golz, H. Schlarb, B. Schmidt, E. Schneidmiller, S. Schreiber, B. Steffen, N. Stojanovic, S. Wunderlich, M.V. Yurkov
DESY, Hamburg, Germany

Funding: The project has been supported by the Federal Ministry of Education and Research of Germany (BMBF) under contract No. 05K10GU2 and FSP301
This paper describes the experimental activity on the generation of very short FEL pulses in the soft x-ray range in the SASE-mode at the high-gain free-electron laser FLASH [1, 2]. The key element, a photo-injector laser which is able to generate laser pulses of about 2 ps FWHM has been optimized and commissioned. It allows the generation of shorter bunches with low bunch charge (of up to 200 pC) directly at the photo-cathode. Initially shorter injector laser pulses and thus shorter bunches eases the required bunch compression factor for short pulses below 10 fs duration which makes operation of the electron beam formation system to be more robust with respect to jitters and collective effects. As a result, overall stability of SASE FEL performance is improved. In the optimal case single-spike operation can be achieved. In this paper the experimental results on production of short electron bunches and the SASE performance using the new injector laser will be shown and the measured electron bunch and FEL radiation properties are discussed. In addition, optimizations of bunch diagnostics for low charge and short bunches are discussed.

Slides TUB04 [1.201 MB]

TUP069

Cavity Length Change vs. Mirror Steering in a Ring Confocal Resonator

cavity, wiggler, FEL, optics

516

S.V. Benson
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-84-ER40150, the Office of Naval Research, and the Joint Technology Office.
In principle, a ring confocal resonator allows for the use of a short Rayleigh length without the extreme sensi-tivity to mirror steering typical in a near-concentric reso-nator [1]. One possible weakness of such a resonator is that the cavity length is no longer independent of the mirror steering. This is one of the strengths of a linear resonator. In this presentation, it is shown that, in a simple 2-dimensional corner cube type ring confocal resonator, the cavity length is, in fact, not dependent on the mirror steering to first order in the mirror angles. Thus the ring-confocal resonator might be a very easy-to-operate and stable resonator for short Rayleigh range operation in FEL oscillators
[1] Stephen Benson, George Neil, Michelle Shinn, Laser and Beam Control Technologies, Santanu Basu, James Riker, Editors, Proceedings of SPIE Vol. 4632 (2002).

TUP073

High Power Operation of the THz FEL at ISIR, Osaka University

FEL, electron, linac, gun

528

K. Kawase, M. Fujimoto, S. Funakoshi, K. Furukawa, A. Irizawa, G. Isoyama, R. Kato, K. Kubo, K. Miyazaki, S. Suemine, A. Tokuchi, R. Tsutsumi, M. Yaguchi
ISIR, Osaka, Japan

The THz FEL at Osaka University is based on the L-band linac that provides a multi-bunch electron beam with an 8 us duration in the energy range from 12.5 to 20 MeV. Although the RF frequency of the linac is 1.3 GHz, the bunch intervals are expanded to 9.2 ns for the FEL using a sub-harmonic buncher system that operates at 10⁸ MHz, to enhance the bunch charge to 1 nC/bunch. The FEL covers the wavelength range from 30 to 150 um, and maximum energies of the macropulse and the micropulse are 3.7 mJ and 11 uJ, respectively, at ~70 um measured at an experimental station. To enhance the FEL power further, the electron beam current cannot be increased simply because the beam loading in the acceleration tube is too high. To solve this problem, we have developed a 27 MHz grid pulser for the thermionic electron gun that makes the bunch intervals 4 times longer and increases charge of the bunch 4 times higher whereas the beam loading is the same as that in the 108 MHz mode. In this new operation mode, where a single FEL pulse lases in the cavity, we have succeeded in obtaining the micropulse energy exceeding 100 uJ at a wavelength of 68 um.

TUP085

FERMI Status Report

FEL, electron, experiment, laser

564

M. Svandrlik, E. Allaria, F. Bencivenga, C. Callegari, F. Capotondi, D. Castronovo, P. Cinquegrana, M. Coreno, R. Cucini, I. Cudin, G. D'Auria, M.B. Danailov, R. De Monte, G. De Ninno, P. Delgiusto, A.A. Demidovich, S. Di Mitri, B. Diviacco, A. Fabris, R. Fabris, W.M. Fawley, M. Ferianis, E. Ferrari, P. Finetti, L. Fröhlich, P. Furlan Radivo, G. Gaio, D. Gauthier, F. Gelmetti, L. Giannessi, M. Kiskinova, S. Krecic, M. Lonza, N. Mahne, C. Masciovecchio, M. Milloch, F. Parmigiani, G. Penco, L. Pivetta, O. Plekan, M. Predonzani, E. Principi, L. Raimondi, P. Rebernik Ribič, F. Rossi, L. Rumiz, C. Scafuri, C. Serpico, P. Sigalotti, C. Spezzani, C. Svetina, M. Trovò, A. Vascotto, M. Veronese, R. Visintini, D. Zangrando, M. Zangrando
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

FERMI, the seeded FEL located at the Elettra laboratory in Trieste, Italy, is now in regular operation for users with its first FEL line, FEL-1, which covers the wavelength range between 100 and 20 nm. We will give an overview of the typical operating modes of the facility for users and we will report on the status of beamlines and experimental stations. Three beamlines are now opened for users, three more are in construction. Meanwhile, the second FEL line of FERMI, FEL-2, a HGHG double stage cascade covering the wavelength range 20 to 4 nm is still under commissioning; we will report on the latest results in particular at the shortest wavelength, 4 nm in the fundamental.

TUP087

The Status of LUNEX5 Project

electron, FEL, laser, undulator

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.

WEB05

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

electron, laser, undulator, 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]

THP002

Beam Energy Management and RF Failure Compensation Scenarios for the European XFEL

linac, klystron, optics, quadrupole

672

B. Beutner
DESY, Hamburg, Germany

The operation of complex systems as the driver linacs for free-electron-lasers is limited by the reliability of the individual components. Failures of RF systems can therefore constrict FEL availability. Typically reserves are included in the overall linac voltage capacity to allow for redistribution of acceleration in case of an RF failure. However, such redistributions of the acceleration of the linac affects the beam dynamics of the machine. While the effects on the optics can easily be compensated by rescaling of the quadrupole magnet strength, the bunch compression set-up requires a more involved investigation. In this paper we discuss studies for an energy management system for the European XFEL.

THP003

Two Charges in the Same Bunch Train at the European XFEL

simulation, laser, emittance, 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

THP046

Cu and Cs2Te Cathodes Preparation and QE History at the SwissFEL Injector Test Facility.

cathode, laser, gun, vacuum

832

J. Bossert, R. Ganter, M. Schaer, T. Schietinger
PSI, Villigen PSI, Switzerland

The installation of a load-lock chamber attached to the SwissFEL gun gives the possibility to carefully prepare the metallic cathodes under vacuum and also to use semiconductor cathodes like Cs2Te cathodes which cannot be transported through air. The paper presents the preparation procedures used for copper (QE>1.e-4) and Cs2Te cathodes (based on a CERN recipe) together with surface analysis results (SEM, EDX, interferometry, microscopy). Finally, the QE evolutions obtained in the SwissFEL Injector test facility as well as in a test stand are discussed for both materials.

THP051

Thyratron Replacement

klystron, network, target, linear-collider

847

I. Roth, M.P.J. Gaudreau, M.K. Kempkes
Diversified Technologies, Inc., Bedford, Massachusetts, USA

Funding: DOE Contract DE-SC0011292
Semiconductor thyristers have long been used as a replacement for thyratrons, at least in low power or long pulse RF systems. To date, however, such thyristor assemblies have not demonstrated the reliability needed for installation in short pulse, high peak power RF stations used with many pulsed electron accelerators. The difficulty is that a fast rising current in a thyristor tends to be carried in a small region, rather than across the whole device, and this localized current concentration can cause a short circuit failure. It is not clear that this failure mode can be overcome with currently available device designs. An alternate solid-state device, the insulated-gate bipolar transistor (IGBT), can readily operate at the speed needed for the accelerator, but commercial IGBTs cannot handle the voltage and current required. Diversified Technologies, Inc. (DTI) has patented and refined the technology required to build these arrays of series-parallel connected switches. Under DOE contract, DTI is currently developing an affordable, reliable, form-fit-function replacement for the klystron modulator thyratrons at SLAC capable of pulsing at 360 kV, 420 A, 6 μs, and 120 Hz.

THP058

Solid-State Switch for a Klystron Modulator for Stable Operation of a THz- FEL

FEL, klystron, electron, linac

868

G. Isoyama, M. Fujimoto, S. Funakoshi, K. Furukawa, A. Irizawa, R. Kato, K. Kawase, K. Miyazaki, A. Tokuchi, R. Tsutsumi, M. Yaguchi
ISIR, Osaka, Japan
F. Kamitsukasa
Osaka University, Graduate School of Science, Osaka, Japan

We have been conducting studies on upgrade of the THz-FEL and its applications, using the L-band electron linac at ISIR, Osaka University. The stability of the FEL is crucial for these studies and the operation of the FEL depends on characteristics of the electron beam, especially on stability of the electron energy, which is strongly affected by the RF power and its phase provided to the linac. We uses a klystron modulator with the a highly stable charging system to the PFN with a fractional variation of 8×10^-5 (peak-to-peak), but the klystron voltage varies by one order of magnitude larger due probably to the thyratron used as a high voltage and high current switch in the klystron modulator. In order to make the stability of the FEL higher, we have developed a solid-state switch using static induction thyristors. The performance of the switch is as follows; the maximum holding voltage is 25 kV, the maximum current is 6 kA for the pulse duration of 10 us, the switching time is 270 ns, and the maximum repetition frequency is 10 Hz. The intensity fluctuation of the FEL macropulse is reduced to a few percents using the solid state switch.

THP059

The Laser Heater System of SwissFEL

laser, undulator, electron, emittance

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)

THP063

Production of C-band Disk-loaded type CG Accelerating Structures

vacuum, cavity, resonance, acceleration

885

N. Shigeoka, S. Miura, D. Suzuki
MHI, Hiroshima, Japan
T. Asaka, T. Inagaki, Y. Otake, T. Sakurai
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
H. Ego
JASRI/SPring-8, Hyogo-ken, Japan

In April 2013, MITSUBISHI HEAVY INDUSTRIES, LTD. contracted with RIKEN to produce six C-band disk-loaded type and constant gradient (CG) accelerating structures for removal of SCSS. These structures were newly designed by RIKEN for operation with an acceleration gradient of over 45 MeV/m and a repletion rate of 120 pps. The first structure was delivered in August 2013 to RIKEN and the other five was also delivered in March 2014. The accelerating structures were stacked from one hundred accelerating cells and formed by the vacuum brazing method. These cells using oxygen free copper were ultra-precisely machined. Unlike the C-band choke-mode type structures, which MHI manufactured in past for SACLA, the accelerating cells of the CG structure can be tuned after the brazing by pushing dimpling at the tuning hole of each cell. Demands of a VSWR < 1.1 and a phase error < 3 degree are fulfilled after the tuning by using the nodal shift method, which corrects cell frequency shifts due to the machining errors of cells and a cell’s deformation by the heat cycle of the brazing. The detailed results of the production and low-power RF tests will be presented in this presentation.

Poster THP063 [0.623 MB]

THP069

Performance Study of High Bandwidth Pickups Installed at FLASH and ELBE for Femtosecond-Precision Arrival Time Monitors

pick-up, laser, electron, experiment

893

M.K. Czwalinna, C. Gerth, H. Schlarb, C. Sydlo
DESY, Hamburg, Germany
A. Angelovski, R. Jakoby, A. Penirschke
TU Darmstadt, Darmstadt, Germany
M. Gensch, M. Kuntzsch
HZDR, Dresden, Germany
M. Kuntzsch
TU Dresden, Dresden, Germany
T. Weiland
TEMF, TU Darmstadt, Darmstadt, Germany

At today's free-electron lasers, high-resolution electron bunch arrival time measurements have become increasingly more important in fast feedback systems for a timing jitter reduction down to the femtosecond level as well as for time-resolved pump-probe experiments. This is fulfilled by arrival time monitors which employ an electro-optical detection scheme by means of synchronised ultrashort laser pulses. Even more, at FLASH and the European XFEL the measurement has to cover a wide range of bunch charges from 1 nC down to 20 pC with equally sub-10 fs resolution. To meet these requirements, recently a high bandwidth pickup electrode with a cut-off frequency above 40 GHz has been developed. These pickups are installed at the macro-pulsed SRF accelerator of the free-electron laser FLASH and at the macro-pulsed continuous wave SRF accelerator ELBE. In this paper we present an evaluation of the pickup performance by direct signal measurements with high bandwidth oscilloscopes and by use of the electro-optical arrival time monitor.

THP075

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

kicker, emittance, electron, 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.

THP090

Femtosecond Timing Distribution for the European XFEL

laser, timing, status, FEL

945

C. Sydlo, M.K. Czwalinna, M. Felber, C. Gerth, T. Lamb, H. Schlarb, S. Schulz, F. Zummack
DESY, Hamburg, Germany
S. Jabłoński
Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland

Accurate timing synchronization on the femtosecond timescale is an essential installation for time-resolved experiments at free-electron lasers (FELs) such as FLASH and the upcoming European XFEL. To date the required precision levels can only be achieved by a laser-based synchronization system. Such a system has been successfully deployed at FLASH and is based on the distribution of femtosecond laser pulses over actively stabilized optical fibers. Albeit its maturity and proven performance this system had to undergo a major redesign for the upcoming European XFEL due to the enlarged number of stabilized optical fibers and an increase by a factor of up to 10 in length. The experience and knowledge gathered from the operation of the optical synchronization system at FLASH has led to an elaborate and modular precision instrument which can stabilize polarization maintaining fibers for highest accuracy as well as economic single mode fibers for shorter lengths. This paper reports on the laser-based synchronization system focusing on the active fiber stabilization units for the European XFEL, discusses major complications, their solutions and and the most recent performance results.

THC04

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

gun, emittance, 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]