SASE FELs

Paper	Title	Page
MOP052	Update on FEL Performance for SwissFEL	140
	E. Prat, S. Reiche PSI, Villigen PSI, Switzerland
	The SwissFEL project under construction at the Paul Scherrer Institute foresees for 2017 the realization of an X-ray FEL with a photon wavelength down to 1 Å. In this paper we present the expected SASE performance for SwissFEL based on input distributions obtained from detailed start-to-end simulation results. The effects of the longitudinal wakefields due to resistive wall and surface roughness in the undulator beamline have been taken into account. We have studied and optimized the impact on the FEL performance of different factors like the electron focusing or the undulator tapering. Results for the standard cases with 200 pC and 10 pC electron bunch charge are shown.
MOP053	SASE FEL Performance at the SwissFEL Injector Test Facility	144
	S. Reiche PSI, Villigen PSI, Switzerland
	A 4 m long prototype of the SwissFEL undulator module with an undulator period length of 15 mm was installed at the SwissFEL Injector Test Facility and tested with a 200 MeV electron beam in the beginning of 2014. We observed FEL lasing in SASE mode in the wavelength range from 70 to 800 nm, tuning the wavelength by energy and gap. The measurements of the FEL performance are reported. on behalf of the SwissFEL Team
MOP054	Harmonic Lasing Options for LCLS-II	148
	G. Marcus, Y. Ding, Z. Huang, T.O. Raubenheimer SLAC, Menlo Park, California, USA G. Penn LBNL, Berkeley, California, USA
	Harmonic lasing can be a cheap and relatively efficient way to extend the photon energy range of a particular FEL beamline. Furthermore, in comparison to nonlinear harmonics, harmonic lasing can provide a beam that is more intense, stable, and narrow-band. This paper explores the application of the harmonic lasing concept at LCLS-II using various combinations of phase shifters and attenuators. In addition, a scheme by which individual undulator modules are tuned to amplify either the third or fifth harmonic in different configurations is presented in detail.
MOP055	Start-to-End Simulations for IR/THz Undulator Radiation at PITZ	153
	P. Boonpornprasert, M. Khojoyan, M. Krasilnikov, F. Stephan DESY Zeuthen, Zeuthen, Germany B. Marchetti, E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany S. Rimjaem Chiang Mai University, Chiang Mai, Thailand
	High brightness electron sources for modern linac-based Free-Electron Lasers (FELs) have been characterized and optimized at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). Since the time structure of the electron bunches at PITZ is identical to those at the European XFEL, the PITZ accelerator is being considered as a proper machine for the development of an IR/THz source prototype for pump and probe experiments planned at the European XFEL. Tunable IR/THz radiation sources using synchrotron radiation from a dipole magnet, transition radiation, high gain FELs and coherent radiation of tailored or premodulated beams are currently under consideration. This work describes start-to-end simulations for generating the FEL radiation using an APPLE-II undulator with electron beams produced by the PITZ accelerator. Analysis of the physical parameter space has been performed with tools of the FAST program code package. Electron Beam dynamics simulations were performed by using the ASTRA code, while the GENESIS 1.3 code was used to study the SASE process. The results of these studies are presented and discussed in this paper.
MOP056	SASE Characteristics from Baseline European XFEL Undulators in the Tapering Regime	159
	I.V. Agapov, G. Geloni XFEL. EU, Hamburg, Germany G. Feng, V. Kocharyan, E. Saldin, S. Serkez, I. Zagorodnov DESY, Hamburg, Germany
	The output SASE characteristics of the baseline European XFEL, recently used in the TDRs of scientific instruments and X-ray optics, have been previously optimized assuming uniform undulators without considering the potential of undulator tapering in the SASE regime. Here we demonstrate that the performance of European XFEL sources can be significantly improved without additional hardware. The procedure consists in the optimization of the undulator gap configuration for each X-ray beamline. Here we provide a comprehensive description of the X-ray photon beam properties as a function of wavelength and bunch charge. Based on nominal parameters for the electron beam, we demonstrate that undulator tapering allows one to achieve up to a tenfold increase in peak power and photon spectral density in the conventional SASE regime.
MOP057	Proposal to Generate 10 TW Level Femtosecond X-ray Pulses from a Baseline Undulator in Conventional SASE Regime at the European XFEL	164
	E. Saldin, V. Kocharyan, S. Serkez, I. Zagorodnov DESY, Hamburg, Germany G. Geloni XFEL. EU, Hamburg, Germany
	Output characteristics of the European XFEL have been previously studied assuming an operation point at 5 kA peak current. Here we explore the possibility to go well beyond such nominal peak current level. We consider a bunch with 0.25 nC charge, compressed up to a peak current of 45 kA. An advantage of operating at such high peak current is the increase of the x-ray output peak power without any modification to the baseline design. Based on start-to-end simulations, we demonstrate that such high peak current, combined with undulator tapering, allows one to achieve up to a 100-fold increase in a peak power in the conventional SASE regime, compared to the nominal mode of operation. In particular, we find that 10 TW-power level, femtosecond x-ray pulses can be generated in the photon energy range between 3 keV and 5 keV, which is optimal for single biomolecule imaging. Our simulations are based on the exploitation of all the 21 cells foreseen for the SASE3 undulator beamline, and indicate that one can achieve diffraction to the desired resolution with 15 mJ (corresponding to about 3·1013 photons) in pulses of about 3 fs, in the case of a 100 nm focus at the photon energy of 3.5 keV.
MOP058	Purified SASE Undulator Configuration to Enhance the Performance of the Soft X-ray Beamline at the European XFEL	169
	V. Kocharyan, E. Saldin, S. Serkez, I. Zagorodnov DESY, Hamburg, Germany I.V. Agapov, G. Geloni XFEL. EU, Hamburg, Germany
	The purified SASE (pSASE) undulator configuration recently proposed at SLAC promises an increase in the output spectral density of XFELs. In this article we study a straightforward implementation of this configuration for the soft x-ray beamline at the European XFEL. A few undulator cells, resonant at a subharmonic of the FEL radiation, are used in the middle of the exponential regime to amplify the radiation, while simultaneously reducing the FEL bandwidth. Based on start-to-end simulations, we show that with the proposed configuration the spectral density in the photon energy range between 1.3 keV and 3 keV can be enhanced of an order of magnitude compared to the baseline mode of operation. This option can be implemented into the tunable-gap SASE3 baseline undulator without additional hardware, and it is complementary to the self-seeding option with grating monochromator proposed for the same undulator line, which can cover the photon energy range between about 0.26 keV and 1 keV.
MOP059	Beam Dynamic Simulations for Single Spike Radiation with Short-Pulse Injector Laser at FLASH	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.
MOP060	Demonstration of SASE Suppression Through a Seeded Microbunching Instability	177
	C. Lechner, A. Azima, M. Drescher, L.L. Lazzarino, Th. Maltezopoulos, V. Miltchev, T. Plath, J. Rönsch-Schulenburg, J. Roßbach Uni HH, Hamburg, Germany S. Ackermann, J. Bödewadt, G. Brenner, M. Dohlus, N. Ekanayake, T. Golz, E. Hass, K. Honkavaara, T. Laarmann, T. Limberg, E. Schneidmiller, N. Stojanovic, M.V. Yurkov DESY, Hamburg, Germany K.E. Hacker, S. Khan, R. Molo DELTA, Dortmund, Germany
	Funding: Supported by Federal Ministry of Education and Research of Germany under contract No. 05K10PE1, 05K10PE3, 05K13GU4, and 05K13PE3 and the German Research Foundation programme graduate school 1355. Collective effects and instabilities due to longitudinal space charge and coherent synchrotron radiation can degrade the quality of the ultra-relativistic, high-brilliance electron bunches needed for the operation of free-electron lasers. In this contribution, we demonstrate the application of a laser-induced microbunching instability to selectively suppress the SASE process. A significant decrease of photon pulse energies was observed at the free-electron laser FLASH in coincidence with overlap of 800 nm laser pulses and electron bunches within a modulator located approximately 40 meters upstream of the undulators. We discuss the underlying mechanisms based on longitudinal space charge amplification [E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 110701 (2010)] and present measurements.
MOP061	Electron Beam Delays for Improved Temporal Coherence and Short Pulse Generation at SwissFEL	181
	N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S. Reiche PSI, Villigen PSI, Switzerland
	Proposals have been made for the introduction of magnetic electron beam delays in between the undulator modules of a long sectional FEL undulator - these can be used for the generation of trains of FEL pulses which can individually be shorter than the FEL cooperation time [*] or to greatly improve the temporal coherence of the FEL output compared to the nominal SASE configuration [**,***,***]. This paper comprises a feasibility study of the application of these techniques to the SwissFEL hard X-Ray beamline. Three-dimensional simulations are used to investigate the potential photon output. [*] N.R. Thompson and B.W.J. McNeil, PRL 100:203901, 2008. [**] N.R. Thompson et al. In Proc IPAC2010, pages 2257–2259, 2010 [***] J. Wu, A. Marinelli, and C. Pellegrini. Proc FEL2012, 2012.
MOP062	FEL Proposal Based on CLIC X-Band Structure	186
	A.A. Aksoy, Ö. Yavaş Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey E. Adli University of Oslo, Oslo, Norway D. Angal-Kalinin, J.A. Clarke STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom M.J. Boland, T.K. Charles, R.T. Dowd, G. LeBlanc SLSA, Clayton, Australia N. Charitonidis, A. Grudiev, A. Latina, D. Schulte, I. Syratchev, W. Wuensch CERN, Geneva, Switzerland G. D'Auria, S. Di Mitri Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy W. Fang, Q. Gu SINAP, Shanghai, People's Republic of China E.N. Gazis National Technical University of Athens, Athens, Greece M. Jacewicz, R.J.M.Y. Ruber, V.G. Ziemann Uppsala University, Uppsala, Sweden Z. Nergiz Nigde University, Nigde, Turkey
	A linear accelerating structure with an average loaded gradient of 100 MV/m at X-Band frequencies has been demonstrated in the CLIC study. Recently, it has been proposed to use this structure to drive an FEL linac. In contrast to CLIC the linac would be powered by klystrons not by an RF source created by a drive beam. The main advantage of this proposal is achieving the required energies in a very short distance, thus the facility would be rather compact. In this study, we present the structure choice and conceptual design parameters of a facility which could generate laser photon pulses below Angstrom. Shorter wavelengths can also be reached with slightly increasing the energy.
MOP063	A Novel Modeling Approach for Electron Beams in SASE FELs	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.
MOP064	Statistical Properties of the Radiation from SASE FEL Operating in a Post-saturation Regime with and without Undulator Tapering	194
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	We describe statistical and coherence properties of the radiation from x-ray free electron lasers (XFEL) operating in the post-saturation regime. We consider practical case of the SASE3 FEL at European XFEL. We perform comparison of the main characteristics of X-ray FEL operating in the post-saturation regime with and without undulator tapering: efficiency, coherence time and degree of transverse coherence.
MOP065	Optimization of a High Efficiency FEL Amplifier	199
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	The problem of an efficiency increase of an FEL amplifier is now of great practical importance. Technique of undulator tapering in the post-saturation regime is used at the existing x-ray FELs LCLS and SACLA, and is planned for use at the European XFEL, Swiss FEL, and PAL XFEL. There are also discussions on the future of high peak and average power FELs for scientific and industrial applications. In this paper we perform detailed analysis of the tapering strategies for high power seeded FEL amplifiers. Application of similarity techniques allows us to derive universal law of the undulator tapering.
MOP066	An Overview of the Radiation Properties of the European XFEL	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	210
	R. Brinkmann, E. Schneidmiller, J.K. Sekutowicz, M.V. Yurkov DESY, Hamburg, Germany
	The European XFEL will operate nominally at 17.5 GeV in SP (short pulse) mode with 0.65 ms long bunch train and 10 Hz repetition rate. A possible upgrade of the linac to CW (continuous wave) or LP (long pulse) modes with a corresponding reduction of electron beam energy is under discussion since many years. Recent successes in the dedicated R&D program allow to forecast a technical feasibility of such an upgrade in the foreseeable future. One of the challenges is to provide sub-Angstroem FEL operation in CW and LP modes. In this paper we perform a preliminary analysis of a possible operation of the European XFEL in the hard X-ray regime in CW and LP modes with the energies of 7 GeV and 10 GeV, respectively. We consider lasing in the baseline XFEL undulator as well as in a new undulator with a reduced period. We show that, with reasonable requirements on electron beam quality, lasing on the fundamental will be possible in sub-Angstroem regime. As an option for generation of brilliant photon beams at short wavelengths we also consider harmonic lasing that has recently attracted a significant attention.
MOP068	Suppression of the Fundamental Frequency for a Successful Harmonic Lasing in SASE FELs	215
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	Harmonic lasing in X-ray FELs has recently attracted a significant attention and is now seriously considered as a potential method for generation of brilliant photon beams at short wavelengths. It is clear, however, that for a successful harmonic lasing one has to suppress the fundamental. In this paper we discuss different methods for such a suppression: phase shifters, intraundulator spectral filtering, switching between the 3rd and the 5th harmonics etc.
TUB01	Review of Coherent SASE Schemes	327
	B.W.J. MᶜNeil, L.T. Campbell, J. Henderson USTRAT/SUPA, Glasgow, United Kingdom D.J. Dunning, N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Funding: We acknowledge STFC Agreement No. 4163192; ARCHIE-WeSt HPC, EPSRC grant EP/K000586/1; John von Neumann Institute for Computing (NIC) on JUROPA at Julich Supercomputing Centre (JSC), project HHH20 A review is presented of some of the methods and their origins that have recently been proposed to improve the temporal coherence of SASE output. These methods do not require any external laser seed field, or the use of the so-called self-seeding methods, where the SASE radiation is optically filtered and improved at an early stage of the interaction before re-injection and amplification to saturation. By using methods that introduce an additional relative propagation between the electron beam and the radiation field, the localised collective interaction, which leads to the formation of the ‘spiking’ associated with normal SASE output, is removed. The result is output pulses which are close to the fourier transform limit without the need for any external seeds or intermediate optics.
	Slides TUB01 [6.256 MB]
TUB02	Generation of Intense XVUV Pulses with an Optical Klystron Enhanced Self- amplified Spontaneous Emission Free Electron Laser	332
	G. Penco, E. Allaria, G. De Ninno, E. Ferrari, L. Giannessi Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy G. De Ninno University of Nova Gorica, Nova Gorica, Slovenia L. Giannessi ENEA C.R. Frascati, Frascati (Roma), Italy
	Fermi is a seeded FEL operating in high gain harmonic generation mode. The FEL layout is constituted by a modulator and six radiators separated by a dispersive section. The modulator and the radiators can be tuned to the same resonant frequency to set up an asymmetric optical klystron configuration where self amplified spontaneous emission can be generated and studied. This paper presents the experiment consisting in the analysis of the enhancement of the self-amplified spontaneous emission (SASE) radiation by the dispersion in the optical klystron. The FEL pulses produced with the optical klystron configuration are several order of magnitude more intense than in pure SASE mode with the dispersion set to zero, The experimental observations are in good agreement with simulation results and theoretical expectations. A comparison with the typical high-gain harmonic generation seeded Fel operation is also provided.
	Slides TUB02 [12.835 MB]
TUB03	FEL Overcompression in the LCLS	337
	J.L. Turner, F.-J. Decker, Y. Ding, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, A. Marinelli, T.J. Maxwell, H.-D. Nuhn, D.F. Ratner, T.J. Smith, J.J. Welch, F. Zhou SLAC, Menlo Park, California, USA
	Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515 Overcompression of the Linac Coherent Light Source (LCLS) x-ray Free Electron Laser (FEL) at the SLAC National Accelerator Center is studied. The studies and operational implications are summarized in this talk.
	Slides TUB03 [4.493 MB]
TUB04	Operation of FLASH with Short SASE-FEL Radiation Pulses	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]