FEL2011 - List of Keywords (emittance)

Paper	Title	Other Keywords	Page
MOPB15	Numerical Simulation of CAEP Compact FEL THz Source	FEL, cavity, simulation, undulator	35
	L.J. Chen, Q.K. Jia USTC/NSRL, Hefei, Anhui, People's Republic of China M. Li, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	Free Election Laser Terahertz source is a good choice for THz source, whose wavelength is tunable. Using 1D FEL stimulation code FELO, we simulate the output characteristic of China Academy of Engineering Physics (CAEP) FEL THz, which is a waveguide FEL oscillator. The beam qualitys’ influence on the operation of FEL, such as energy dispersion, emittance and beam current, have been studied to designate a set of beam parameters. Besides, the output performance of FEL at different output coupling ratio is analyzed. The cavity detuning is discussed too. Meanwhile the influence of the position of the undulator in the cavity on the FEL performance is also studied.

MOPB17	Harmonic Generation for a Hard X-ray FEL	electron, undulator, FEL, bunching	41
	Q.R. Marksteiner, K. Bishofberger, B.E. Carlsten, L.D. Duffy, N.A. Yampolsky LANL, Los Alamos, New Mexico, USA
	Funding: We gratefully acknowledge the support of the US Department of Energy through the LANL LDRD Propgram for this work. The proposed MaRIE XFEL at Los Alamos National Laboratory will generate ¼ Å, longitudinally coherent x-rays with a 20 GeV electron beam. A masked emittance exchanger can be used to generate coherent electron bunching at nm wavelengths. This masked emittance exchanger must be at 1 GeV in the accelerator, in order to mitigate debunching from incoherent synchrotron radiation (ISR). After this, the harmonic content must be stepped up by a factor of 200 in frequency and the electrons must be accelerated to 20 GeV. The nonlinear debunching effects in the accelerator from emittance must be mitigated by keeping the beam transversely large. There are several schemes to step the coherent bunching up to higher harmonics, all which require modulator and dispersive sections [1]. Echo-Enhanced Harmonic Generation, which requires large dispersion, must be incorporated at low energies, where ISR is reduced. Here we compare the usefulness of different harmonic generation schemes, and examine the possibility of placing successive harmonic generation sections at energies lower than 20 GeV in the accelerator line, with the accelerator sections in between used to introduce dispersion to the beam. [1] Phys. Rev. E 71, 046501 (2005), etc.

MOPB20	Effect of Coulomb Collisions on Echo-Enabled Harmonic Generation (EEHG)	bunching, FEL, scattering, undulator	49
	G.V. Stupakov SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. DOE Contract No. DE-AC02-76SF00515. Echo-enabled harmonic generation (EEHG) for FEL seeding uses two undulator-modulators and two chicanes to introduce a fine structure into the beam longitudinal phase space which, at the end of the system, transforms into high harmonic modulation of the beam current. As a result of this phase space manipulation, after the first chicane, the energy distribution function becomes a rapidly modulated function of energy, with the scale of the modulation of the order of the initial energy spread of the beam divided by the EEHG harmonic number. Small-angle Coulomb collisions between the particles of the beam (also known as intrabeam scattering) tend to smear out this modulation and hence to suppress the beam bunching. In this paper we calculate the EEHG bunching factor with account of the collisions and derive a simple scaling relation for the strength of the effect. Our estimates show that collisions become a limiting factor in EEGH seeding for harmonic numbers roughly exceeding 100.

MOPB30	The Effects of Betatron Motion on the Preservation of FEL Microbunching	electron, betatron, bunching, undulator	81
	G. Geloni European XFEL GmbH, Hamburg, Germany V. Kocharyan, E. Saldin DESY, Hamburg, Germany
	In some options for circular polarization control at X-ray FELs, a helical radiator is placed a few ten meters distance behind the baseline undulator. If the microbunch structure induced in the baseline (planar) undulator can be preserved, intense coherent radiation is emitted in the helical radiator. The effects of betatron motion on the preservation ofμbunching in such in-line schemes should be accounting for. In this paper we present a comprehensive study of these effects. It is shown that one can work out an analytical expression for the debunching of an electron beam moving in a FODO lattice, strictly valid in the asymptote for a FODO cell much shorter than the betatron function. Further on, numerical studies can be used to demonstrate that the validity of such analytical expression goes beyond the above-mentioned asymptote, and can be used in much more a general context. Finally, a comparison with Genesis simulations is given.

MOPB32	System Trade Analysis for an FEL Facility	FEL, undulator, photon, linac	89
	M.W. Reinsch, B. Austin, J.N. Corlett, L.R. Doolittle, G. Penn, D. Prosnitz, J. Qiang, A. Sessler, M. Venturini, J.S. Wurtele LBNL, Berkeley, California, USA
	Designing an FEL from scratch requires the design team to balance multiple science needs, FEL and accelerator physics constraints and engineering limitations. STAFF (System Trade Analysis for an FEL Facility) enables the user to rapidly explore a large range of Linac and FEL design options. The model utilzes analytical models such as the Ming Xie formulas when appropriate and look-up tables when necessary to maintain speed, flexibility and extensiblity. STAFF allows for physics models for FEL harmonics, wake fields, cavity higher-order modes and aspects of linac particle dynamics. The code will permit the user to study error tolerances and multiple beamlines so as to explore the full capabilities of an entire user facility. This makes it possible to optimize the integrated system in terms of performance metrics such as photons/pulse, photons/sec and tunability range while ensuring that unrealistic requirements are not put on either the electron beam quality, undulator field/gap requirements or other system elements. This paper will describe preliminary results from STAFF as applied to a CW FEL soft X-ray facility.

MOPC06	X-Ray FELs Based on ERL Facilities	FEL, radiation, undulator, electron	111
	A. Meseck HZB, Berlin, Germany G.H. Hoffstaetter, F. Löhl, C.E. Mayes CLASSE, Ithaca, New York, USA
	The characteristic high repetition rate and the high spectral brightness of the electron beams delivered by ERLs have led to a large number of ERL based proposals for hard X-ray sources including X-ray FELs. FEL oscillators, including those proposed for hard X-rays, require comparatively low peak currents and are particularly suitable for ERLs. However single-pass FELs in SASE or seeded mode do not seem out of reach when bunch-compression schemes for higher peak currents are utilized. Using the proposed Cornell ERL as an example, we present and discuss oscillator and single-pass FEL schemes which provide extremely high spectral-brightness ultra-short X-ray pulses for experiments.

MOPC12	Coherent Synchrotron Radiation and Bunch Compression Studies in the Emittance Exchange Beamline at the Fermilab A0 Photoinjector	radiation, polarization, cavity, synchrotron	121
	J.C.T. Thangaraj, M.D. Church, H.T. Edwards, A.S. Johnson, A.H. Lumpkin, J. Ruan, J.K. Santucci, Y.-E. Sun, R.M. Thurman-Keup Fermilab, Batavia, USA T.J. Maxwell, P. Piot Northern Illinois University, DeKalb, Illinois, USA
	One of goals of the Fermilab A0 photoinjector is to investigate experimentally the transverse to longitudinal emittance exchange principle. Coherent synchrotron radiation in the emittance exchange line could limit short pulse operation of the emittance exchanger. In this paper, we present experimental and simulation study of the coherent synchroton radiation (CSR) in the emittance exchange line at A0 photoinjector. We also show how EEX can be used to compress a bunch by adding chirp to the incoming beam.

MOPC14	Infrared Single Spike Pulses Generation Using a Short Period Superconducting Tape Undulator at APEX	undulator, FEL, space-charge, electron	129
	D. Filippetto, C. F. Papadopoulos, G. Penn, S. Prestemon, F. Sannibale LBNL, Berkeley, California, USA C. Pellegrini UCLA, Los Angeles, California, USA M. Yoon POSTECH, Pohang, Kyungbuk, Republic of Korea
	Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 We report on the possibility of constructing an infrared FEL by combining a novel design super-conducting undulator developed at LBNL with the high brightness beam from the APEX injector facility at the Lawrence Berkeley National Laboratory. Calculations show that the resulting FEL is expected to deliver a saturated power of about a MW within a 4 m undulator length when operating in Self-Amplified-Spontaneus-Emission mode, with a single-spike of coherent radiation at 2 μm wavelength. The sub-cm undulator periods, associated with the relatively low energy of the APEX beam (20-25 MeV), forces the FEL to operate in a regime with unusual and interesting characteristics. The alternative option of laser seeding the FEL is also examined, showing the potential to reduce the saturation length even further.

TUOBI3	Operational Experience at LCLS	undulator, linac, electron, FEL	166
	H. Loos SLAC, Menlo Park, California, USA
	Funding: *Work supported by DOE contract DE-AC02-76SF00515 The Linac Coherent Light Source (LCLS) X-ray FEL has been operational since 2009 and is delivering soft and hard x-rays to users now in the 4th user run. Reliable operation to deliver x-rays to users, quick machine turn on after shutdowns, and fast configuration changes for the wide range of user requests are particularly important for a facility serving a single user at a time. This talk will discuss procedures to set-up and optimize the accelerator and FEL x-ray beam for user operation. The emphasis will be on the most relevant diagnostics and tuning elements as well as the experience with feedback systems and high level support software to automate FEL operation.
	Slides TUOBI3 [3.074 MB]

TUOC3	High QE, Low Emittance, Green Sensitive FEL Photocathodes Using K₂CsSb	electron, laser, cathode, gun	179
	H.A. Padmore, D. Dowell, J. Feng, T. Vecchione, W. Wan LBNL, Berkeley, California, USA I. Ben-Zvi Stony Brook University, Stony Brook, USA T. Rao, J. Smedley BNL, Upton, Long Island, New York, USA
	Funding: Work was supported by the Director, Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231, KC0407-ALSJNT-I0013, and DE-SC0005713. We describe the development of photocathodes based on Potassium-Cesium-Antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light and low transverse emittance. We have demonstrated QE of 7% at 532 nm, a normalized transverse emittance of 0.36 μm at 543 nm and 3 MV/m field gradient[1]. We have also shown that the material can be relatively robust to residual water contamination and we have extracted current densities of 1 mA/mm² with very long lifetime. We believe that this work is an important step forward in FEL development where high repetition rate is required. [1] Applied Physics Letters (submitted)
	Slides TUOC3 [4.825 MB]

TUPA15	Status of the SwissFEL Facility at the Paul Scherrer Institute	FEL, undulator, linac, electron	223
	S. Reiche Paul Scherrer Institut, Villigen, Switzerland
	SwissFEL is a X-ray Free-electron Laser facility with a soft and hard X-ray beamline, planned to be built at the Paul Scherrer Institute and to be finished in 2016. It covers the wavelength range from 1 Angstrom to 7 nm. In addition to the SASE operation at the entire wavelength, seeding is foreseen down to a wavelength of 1 nm. We report in this presentation the status of the SwissFEL facility, including the layout, the timeline of the project, the different operation modes and the expected performance of the FEL beamlines.

TUPA18	Considerations about Optics-Based Phase-Space Measurements at Linac-Based FEL Facilities	optics, quadrupole, lattice, diagnostics	231
	B. Beutner, E. Prat Paul Scherrer Institut, Villigen, Switzerland
	Transverse phase-space measurements are an essential issue for FEL facilities. After acceleration in the injector the energy is sufficiently high to bring the beam out of the space-charge dominated regime, thus optics based techniques are favored. The beam moments at a given point in the machine are fitted to beam size values downstream with different phase advances between the reconstruction and the measurement point. Two principle methods are possible. Beam sizes can be measured at different positions in the beam line keeping the lattice unchanged. The other possibility is to actively change quadrupoles and use only one screen. These two techniques are compared in this paper including monte-carlo studies on systematic errors using the SwissFEL Injector Test Facility as an example. On the other hand beam size measurements, which are done with OTR screens at SwissFEL Injector Test Facility, are critical for such measurements. An analysis of these images can be an issue, especially if the signal-to-noise is compromised for example by low bunch charges. This study on the phase-space measurement techniques will be completed by a discussion of the image post-processing procedures.

TUPA25	EEHG Seeding Design for SwissFEL	bunching, laser, electron, FEL	251
	E. Prat, S. Reiche Paul Scherrer Institut, Villigen, Switzerland
	The SwissFEL facility, planned at the Paul Scherrer Institute, is based on the SASE operation of a hard (1-7 Å) and a soft (7-70 Å) X-ray FEL beamline. In addition, seeding is foreseen for the soft X-ray beamline, down to a wavelength of 1 nm. The Echo-Enabled Harmonic Generation (EEHG) scheme, which utilizes a rather complex manipulation of the longitudinal phase space distribution of the electron beam to generate high harmonic density modulation, is presently considered the first choice for seeding at SwissFEL. However, EEHG is highly demanding and complex at 1 nm, therefore other strategies like High-Harmonic Generation (HHG) and self-seeding are also evaluated. This paper presents the current status of the seeding design for SwissFEL based on EEHG.

TUPA31	Transverse Phase-space Studies for the Electron Optics at the Direct XUV-seeding Experiment at FLASH (DESY)	undulator, electron, simulation, diagnostics	263
	S. Ackermann, V. Miltchev, J. Roßbach Uni HH, Hamburg, Germany
	Funding: BMBF under contract No. 05 ES7GU1 - DFG GrK 1355 - Joachim Herz Stiftung During the shutdown in 2009/2010 the Free-Electron Laser in Hamburg (FLASH) was upgraded with an experiment to study the high-gain-FEL amplification of a laser ‘‘seed'' from a high harmonic generation (HHG) source in the XUV wavelength range-sFLASH. For an optimal FEL-performance knowledge of the electron bunch transverse phase-space as well as control on the electron optics parameters is required. In this contribution the technical design, the present status and the commissioning results of the sFLASH diagnostic stations will be presented. The possible options for transverse phase space characterization will be discussed. An emphasis will be put on the error analysis and the tolerance estimations. Analysis of experimental data from both OTR-screens and wire scanners will be presented and discussed.

TUPB12	Combined Optimization of a Linac-based FEL Light Source Using a Multiobjective Genetic Algorithm	linac, FEL, electron, cavity	283
	C. F. Papadopoulos, D. Filippetto, G. Penn, J. Qiang, F. Sannibale, M. Venturini LBNL, Berkeley, California, USA
	Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 We report on the development status and preliminary results of a combined optimization scheme for a linac-based, high repetition rate, soft X-ray FEL. The underlying model includes the injector and linac parts of the machine, and the scheme will integrate the design process of these components toward the optimization of the FEL performance. For this, a parallel, multi-objective genetic algorithm is used. We also discuss the beam dynamics considerations that lead to the choices of objectives, or figure-of-merit beam parameters, and describe numerical solutions compatible with the requirements of a high repetition rate user facility.

TUPB13	Beam Dynamics Considerations for APEX a High Repetition Rate Photoinjector	FEL, gun, electron, space-charge	287
	C. F. Papadopoulos, D. Filippetto, F. Sannibale, R.P. Wells LBNL, Berkeley, California, USA
	Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 The Advanced Photoinjector EXperiment is a photo-injector project at Lawrence Berkeley National Lab, designed to test the performance of a high repetition rate (>1 MHz) VHF normal conducting electron gun. The requirements of high beam brightness, as well as significant compression at low energy determine the base setup for the injector transport line. The beam dynamics considerations for a high repetition rate injector are discussed and the potential to use multiple bunch charges that require different tunings of the base setup is explored.

TUPB19	Design and Beam Dynamics Simulation for the Photoinjector of Shanghai Soft X-ray Free Electron Laser Test Facility	laser, gun, linac, simulation	299
	W.-H. Huang, Q. Du, Y.-C. Du, H.J. Qian, C.-X. Tang, L.X. Yan TUB, Beijing, People's Republic of China
	The Shanghai soft X-ray free electron laser test facility (SXFEL) aims to radiate at 9 nm based on the cascaded high-gain harmonic-generation (HGHG) scheme. The photoinjector of SXFEL consists of Ti-sapphire driving laser system, S-band photocathode RF gun, booster linacs, laser heater, beam diagnostics and matching section. It will produce ~130 MeV electron beam in high charge regime (~0.5 nC) with a baseline transverse emittance of 1.5 mm-mrad. This paper will present basic designs and beam dynamics simulations of SXFEL photoinjector.

TUPB28	Considerations for a Light Source Test Facility at Daresbury Laboratory	undulator, electron, FEL, laser	308
	N. Thompson STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom J.A. Clarke, D.J. Dunning, J.W. McKenzie Cockcroft Institute, Warrington, Cheshire, United Kingdom
	This paper considers design options for a dedicated light source test facility at Daresbury Laboratory in the United Kingdom. The facility layout should be easily configurable to enable exploration of many research themes including: ultrashort pulse generation; seeding and harmonic generation; direct laser/electron beam interactions; compact FELs; high brightness photoinjectors. The strategy is to develop and demonstrate novel concepts and expertise relevant to future generations of FEL-based light sources, significantly shortening the R&D phase of any future light source in the UK.

WEPA01	Commissioning of a Photoinjector in HLS	laser, cathode, solenoid, gun	331
	Z.G. He, Q.K. Jia, B.G. Sun, X.H. Wang USTC/NSRL, Hefei, Anhui, People's Republic of China
	A BNL type photoinjector was installed in HLS (Hefei Light Source) and commissioning work was carrying out in last months. The dark current was measured when the high power testing of the gun was processed. The quantum efficiency (QE) of the photocathode was measured and studied, the main parameters of beam quality such as electric charge, transverse emittance and energy were measured and presented in this paper.

WEPA06	Experimental Studies with Spatial Gaussian-cut Laser for the LCLS Photocathode Gun	laser, simulation, cathode, electron	341
	F. Zhou, A. Brachmann, P. Emma, A. Gilevich, Z. Huang SLAC, Menlo Park, California, USA
	Funding: U.S. Department of Energy under contract DE-AC02-76SF00515 To further enhance the LCLS injector performances or simplify its operating conditions, we are evaluating the various parameters including the photocathode drive laser. Simulations show that both the projected and time-sliced emittances with spatial Gaussian profiles having reasonable tail-cutoff are better than those with uniform one. The simulated results are also supported by theoretical analyses. In the LCLS, the spatial uniform or quasi-Gaussian laser profiles are conveniently obtained by adjusting the optics of telescope upstream of an iris, used to define laser size on the cathode. Preliminary beam studies at the LCLS show that both the projected and time-sliced emittances with spatial quasi-Gaussian laser are almost as good as, although not better than, those with uniform one, and also laser transmission through the iris with the quasi-Gaussian is twice that with uniform one, which is to ease copper cathode operations and thus improve the LCLS operation efficiency. More beam studies are planned in the coming summer to measure FEL performances with the quasi-Gaussian in comparison with the uniform one. All simulations and measurements are presented.

WEPA21	Research of Emittance Compensation of CAEP CW DC-Gun Photoinjector	solenoid, gun, space-charge, electron	377
	P. Li, M. Li, D. Wu, Z. Xu, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	Emittance growth is very import for photo-cathode injector due to space charge effect. The emittance compensation technology will be used on the 350 kV photo-cathode DC gun for the CAEP CW FEL, where the energy of electron beam is extremely low and Emittance growth is great severity. In this paper, the space charge force and its effect on electron beam transverse emittance is discussed, the principle of emittance compensation in phase space is analyzed. And a solenoid for emittance compensation is designed. Its beam dynamics has been studied by the PARMELA code. Simulation results indicate that the normalized transverse RMS emittance for electron beam of 80 pC is 1.267 mm•mrad with σ_r=1.5 mm, σ_z=4.25 pS.

WEPB15	Reversible Electron Beam Heater for Suppression of Microbunching Instabilities Based on Transverse Deflecting Cavities	linac, FEL, simulation, laser	409
	C. Behrens DESY, Hamburg, Germany Z. Huang, D. Xiang SLAC, Menlo Park, California, USA
	The presence of the microbunching instability due to the compression of high-brightness electron beams at existing and future X-ray free-electron lasers (FEL) results in restrictions on the attainable lasing performance and renders diagnostics like beam imaging with optical transition radiation impossible. The instability can be suppressed by introducing additional energy spread, i.e. heating the beam, as demonstrated by the successful operation of the laser heater system at the Linac Coherent Light Source. The increased energy spread is typically tolerable for self-amplified spontaneous emission FELs but limits the effectiveness of seeded FELs. In this paper, we present a reversible electron beam heating system based on two transverse deflecting cavities (TCAV) in front and behind a bunch compressor chicane. The additional energy spread will be introduced in the first TCAV, which suppresses the microbunching instability, and then will be eliminated in the second TCAV. We show the feasibility of the suppression of microbunching instabilities based on calculations and simulations, and set limits to the acceptable jitter tolerances.

WEPB20	The Design Of A Multi-Beam Electron Gun For A Photonic Free-Electron Laser	gun, cathode, electron, beam-transport	427
	J.H.H. Lee, K.-J. Boller, T. Denis, P.J.M. van der Slot Mesa+, Enschede, The Netherlands
	Funding: This research is supported by the Dutch Technology Foundation STW, applied science division of NWO and the Technology Program of the Ministry of Economic Affairs. The photonic Free-Electron Laser (pFEL) is a novel slow-wave device which relies on a photonic crystal (PhC) to synchronize the Cherenkov electromagnetic radiation generated from the co-propagating electron beams. The advantage of pFEL is in its frequency- and power-scaling properties. The scale invariance of Maxwell’s equations allows the use of the same beam energy to operate at higher frequencies when the PhC is correspondingly scaled. On the other hand, power-scaling is achieved by varying the number of electron beams propagating in parallel through the PhC. To produce a set of parallel beams, we have designed a multi-beam electron gun using flat cathodes, which produces a total current of 1 A at a beam voltage of 14 kV. We will present the design of this gun together with the expected performance. In addition, we have investigated the beam transport system and will discuss the options for guiding the beams through the PhC.

THOA3	Demonstration of Transverse-to-longitudinal Emittance Exchange at A0 Photoinjector	cavity, space-charge, radiation, booster	443
	J. Ruan, A.S. Johnson, A.H. Lumpkin, Y.-E. Sun, R.M. Thurman-Keup Fermilab, Batavia, USA
	The 3-D phase-space manipulation of electron beams enhances the performance of next generation accelerators including high energy colliders and accelerator based light sources. In this paper we will report an observation of near ideal transverse to longitudinal emittance exchange at the Fermilab A0 Photoinjector. The emittance exchange (EEX) beamline consists a 3.9 GHz normal conducting deflecting mode cavity positioned between two magnetic doglegs. We will also compare the experiment results to simulations.

THOA4	Three Bunch Compressor Scheme for SASE FEL	linac, FEL, undulator, electron	447
	H.-S. Kang, I.S. Ko, S.H. Nam PAL, Pohang, Kyungbuk, Republic of Korea M.-H. Cho, C.H. Yi POSTECH, Pohang, Kyungbuk, Republic of Korea
	The bend angle of dipoles in bunch compressor needs to be small enough to reduce the emittance increase due to CSR, which requires a larger energy chirp at the preceding RF linac. Correlated energy spread is not reduced below FEL parameter after the following RF linac because of the small number of accelerating sections as in the PAL XFEL design. Three bunch compressor scheme can make it possible to minimize the CSR induced emittnace growth as well as reduce the correlated energy spread below FEL parameter.
	Slides THOA4 [1.467 MB]

THOB2	Advanced Beam Dynamics Experiments at SPARC	gun, radiation, laser, electron	451
	A. Bacci, D. Alesini, M. Bellaveglia, M. Castellano, E. Chiadroni, G. Di Pirro, A. Drago, M. Ferrario, A. Gallo, G. Gatti, A. Ghigo, E. Pace, A.R. Rossi, C. Vaccarezza INFN/LNF, Frascati (Roma), Italy A. Cianchi Università di Roma II Tor Vergata, Roma, Italy M. Del Franco, L. Giannessi, A. Petralia, M. Quattromini, C. Ronsivalle, V. Surrenti ENEA C.R. Frascati, Frascati (Roma), Italy S. Lupi Coherentia, Naples, Italy B. Marchetti INFN-Roma II, Roma, Italy A. Mostacci, L. Palumbo Rome University La Sapienza, Roma, Italy V. Petrillo Universita' degli Studi di Milano, Milano, Italy L. Serafini Istituto Nazionale di Fisica Nucleare, Milano, Italy M. Serluca INFN-Roma, Roma, Italy
	The successful operation of the SPARC injector in the Velocity Bunching (VB) mode (bunches with 1 kA current with emittance of 3 mm-mrad have been produced) has opened new perspectives to conduct advanced beam dynamics experiments with ultra-short electron pulses able to extend the THz spectrum or to drive the FEL in the SASE Single Spike mode. A new technique called Laser Comb, able to generate a train of short pulses with high repetition rate, has been extensively tested in the VB configuration. Two electron beam pulses 300 fs long separated by 1 ps have been characterized and the spectrum produced by the SASE interaction has been observed, showing that both pulses have been correctly matched to the undulator and were both lasing. In this paper we report the experimental and theoretical results obtained so far.
	Slides THOB2 [6.673 MB]

THPA02	Two-dimensional Effects on the Behavior of the CSR Force In a Bunch Compression Chicane	electron, FEL, optics, dipole	469
	R. Li, R.A. Legg, B. Terzić JLAB, Newport News, Virginia, USA J. Bisognano, R.A. Bosch UW-Madison/SRC, Madison, Wisconsin, USA
	Funding: This work was supported by U.S. DOE under Contract No. DE-AC05-06OR23177. The endeavor to reach higher brightness of electron bunches in the design of future FEL is seriously challenged by the CSR effect in magnetic bends. Extensive studies on the CSR effects have shown that the 1D approximation of the CSR force is valid for a wide parameter regime. However, as the bunch gets increasingly compressed in the compression process, the behavior of the CSR interaction force will be influenced by the evolution of the 2D bunch distribution. Here we explore this 2D effect using semi-analytical and numerical study of the retarded potentials for an evolving 4D Gaussian phase space distribution with initial energy chirp. We will present results of our systematic exploration of this two-dimensional effect. We will display the interesting dependence of the 2D CSR force on the initial horizontal emittance and uncorrelated energy spread around minimum bunch length, and show the comparison of these results with their 1D counterpart. Physical interpretation will also be discussed.

THPA06	Emittance for Different Bunch Charges at the Upgraded PITZ Facility	gun, laser, booster, cavity	473
	S. Rimjaem, G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, A. Shapovalov, F. Stephan, G. Vashchenko, S. Weidinger DESY Zeuthen, Zeuthen, Germany M. Hoffmann, H. Schlarb DESY, Hamburg, Germany M.A. Nozdrin JINR, Dubna, Moscow Region, Russia D. Richter HZB, Berlin, Germany I.H. Templin, I. Will MBI, Berlin, Germany
	Optimizations of electron sources for short-wavelength Free Electron Laser (FELs) at the Photo Injector Test facility at DESY, location Zeuthen (PITZ) have been continued with a new radio frequency (RF) gun cavity, a new post-accelerating Cut Disk Structure (CDS) booster cavity and several upgraded diagnostic components. The new booster cavity allows stable operation with higher acceleration and longer pulse trains than the operation with the previous TESLA type cavity. Electron beams with a maximum mean momentum of about 25 MeV/c can be produced with the setup described in this paper. Together with the upgraded RF system for the gun and the new CDS booster cavity, the electron beam stability was significantly improved. A large fraction of the measurement program in 2010-2011was devoted to study the dependence of the transverse projected emittance on the bunch charge. Measurement results using this upgraded facility are reported and discussed.

THPA08	An Option of High Charge Operation for the European XFEL	electron, laser, FEL, gun	481
	M. Krasilnikov, H.-J. Grabosch, M. Groß, L. Hakobyan, Ye. Ivanisenko, G. Klemz, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, S. Rimjaem, F. Stephan, G. Vashchenko, S. Weidinger DESY Zeuthen, Zeuthen, Germany G. Asova INRNE, Sofia, Bulgaria I.I. Isaev, A. Shapovalov MEPhI, Moscow, Russia M.A. Khojoyan ANSL, Yerevan, Armenia D. Richter HZB, Berlin, Germany E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany I.H. Templin, I. Will MBI, Berlin, Germany
	The 1.3 GHz superconducting accelerator developed in the framework of TESLA and the European XFEL project holds potential to accelerate high charge electron beams. This feature has been successfully demonstrated during the first run of the free electron laser at the TESLA Test Facility with lasing driven by electron bunches with a charge of up to 4 nC. Currently DESY and the European XFEL GmbH perform revision of the baseline parameters for the electron beam. In this report we discuss a potential option of operation of the European XFEL driven by high charge (1 nC to 3 nC) electron beams. We present the results of the production and characterization of high charge electron bunches. Experiments have been performed at PITZ and demonstrated good properties of the electron beam in terms of emittance. Simulations of the radiation properties of SASE FELs show that application of high charge electron beams will open up the possibility to generate radiation pulse energies up to a few hundred milli-Joule level.

THPA15	Simulation Studies of Generating Ultra Short Pulses at PITZ	laser, electron, simulation, cathode	499
	M.A. Khojoyan, M. Krasilnikov, A. Oppelt, F. Stephan DESY Zeuthen, Zeuthen, Germany M.A. Khojoyan ANSL, Yerevan, Armenia
	Generation of the ultra short electron bunches (<10fs bunch length) which have a small transverse phase space volume and relatively small energy spread is of great interest. Such bunches are required for fully coherent (transversally and longitudinally) FEL radiation (single spike lasing) and for plasma acceleration experiments. The Photo Injector Test Facility at DESY in Zeuthen has already demonstrated the possibility to generate and characterize high quality electron beams for a wide range of bunch charges. Currently electron bunches have a typical length of several ps. To study the possibility of producing short electron bunches at PITZ many beam dynamics simulations have been performed for 1pC bunch charge using the ASTRA code. The current PITZ beam line is supposed to be extended by a small magnet chicane. Several temporal profiles of the cathode laser pulse have been used for the simulations to produce ultra-short electron bunches with small transverse sizes. The results of the beam dynamics simulations are presented and discussed.

THPA23	Investigations on Thermal Emittance at PITZ	laser, electron, cathode, simulation	519
	M. Otevřel, G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, B. Petrosyan, D. Richter, S. Rimjaem, A. Shapovalov, F. Stephan, G. Vashchenko, S. Weidinger DESY Zeuthen, Zeuthen, Germany S. Lederer DESY, Hamburg, Germany
	The main aim of the Photo-Injector Test Facility at DESY, location Zeuthen (PITZ) is to develop and test an FEL photo-injector system capable of producing high charge electron bunches of lowest possible transverse emittance, which has a fundamental impact on FEL performance. Recent measurement results at PITZ showed a fairly small electron beam transverse projected emittance [1] which increased interest in the thermal emittance and its contribution to the overall electron beam emittance budget. Therefore thermal emittance was investigated at PITZ. Results of these studies are presented and discussed.

THPA30	First Results with Tomographic Reconstruction of the Transverse Phase Space at PITZ	laser, booster, cathode, gun	543
	G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, S. Rimjaem, F. Stephan, G. Vashchenko DESY Zeuthen, Zeuthen, Germany G. Asova INRNE, Sofia, Bulgaria D. Richter HZB, Berlin, Germany
	The development of high brightness electron sources capable to drive FELs like FLASH and European XFEL is a major objective of the Photo-Injector Test Facility at DESY in Zeuthen, PITZ. A key parameter used to define the beam quality at PITZ is the transverse phase-space density distribution and its evolution along the beamline. Complementary to the standard phase-space measurement setup constituting slit-scan stations, a module for tomographic diagnostics has been commissioned in 2010/2011. It consists of four observation screens separated by FODO cells and an upstream matching section. The expected advantages of the tomography method are the possibility to measure both transverse planes simultaneously and an improved resolution for low charges and short pulse trains. The fundamental challenges are related to strong space-charge forces at low beam momentum of only 25~MeV/c at PITZ at the moment. Such a constraint presents an obstacle to obtain beam envelope parameters well-matched to the optics of the FODO lattice. This contribution presents the first practical experience with the phase-space tomography module.

THPB02	Implementation of 2D-emittance Compensation Scheme in the BERLinPro Injector	space-charge, booster, linac, solenoid	564
	A.V. Bondarenko, A.N. Matveenko HZB, Berlin, Germany
	Helmholtz-Zentrum Berlin officially started Jan. 2011 the design and construction of the Berlin Energy Recovery Linac Project BERLinPro. The initial goal of this compact ERL is to develop the ERL accelerator physics and technology required to accelerate a high-current (100 mA) low emittance beam (1 mm•mrad normalized), as required for future ERL-based synchrotron light sources. High power ERL based FELs demand low emittance, high peak and average current beams. The injection energy in an ERL is usually rather low to decrease power consumption and avoid activation of the beam dump. Therefore, the space charge is the main reason of the emittance degradation in the injector. The implementation of an emittance compensation scheme in the injector is necessary to achieve a low emittance. Since injector’s optics is axially non-symmetric, the 2D-emittance compensation scheme [1] should be used. The implementation of the 2D-emittance compensation scheme at BERLinPro injector is presented in this contribution. Other sources of emittance growth in ERL injectors are also discussed. [1] S.V. Miginsky, "Emittance compensation of elliptical beam", NIM A 603 (2009), pp 32-34.

THPB15	Metal Cathodes with Reduced Emittance and Enhanced Quantum Efficiency	cathode, FEL, electron, photon	586
	C.M.R. Greaves, J. Feng, H.A. Padmore, W. Wan LBNL, Berkeley, California, USA D. Dowell AES, Princeton, New Jersey, USA
	In this paper, we report experimental results on photoemission from copper and silver surfaces. Using the technique of angle resolved photoemission spectroscopy (ARPES), we demonstrate that, for excess energy around 0.5 eV, the photoelectrons from the Cu(111) and Ag(111) surfaces generated by p-polarized light originate primarily from the well-known surface state with normalized emittance only a fraction of that of the polycrystalline copper cathode presently used in the RF guns. Meanwhile, we demonstrate that the enhancement of the quantum efficiency (QE) at grazing angle is closely related to the surface state as well. Furthermore, we show that the surface state can be easily restored by a simple anneal process, thus pointing to a practical way to reducing the emittance and QE of a metal cathode simultaniously.

THPB19	Investigations of OTR Polarization Effects in Beam-profile Monitors	polarization, optics, radiation, electron	594
	A.H. Lumpkin, A.S. Johnson, J. Ruan, R.M. Thurman-Keup Fermilab, Batavia, USA
	Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. The characterization of transverse beam size using optical transition radiation (OTR) imaging is a well-established technique at many accelerators including the Fermilab A0 photoinjector (A0PI) facility. However, there is growing empirical evidence that the utilization of the polarization component orthogonal to the dimension of interest results in a smaller observed projected image profile. We have continued investigations of this phenomenon with a more controlled experiment where the linear polarizers are selectable in a filter wheel which also included a blank glass position to compensate for the optical path. The aperture for light collection is thus kept fixed compared to our previous tests. We also have balanced the digital camera gain to present similar signal levels to the data analysis program for both the total OTR and the polarized components. At the relatively low Lorentz factor (gamma) of 30, we observed 10-15% projected profile size reductions on a 65-micron beam size case with the perpendicularly polarized components. This anomalous effect in magnitude is compared to results from a standard OTR point-spread-function model.

THPB21	Extraction Arc for FLASH2	extraction, simulation, septum, electron	601
	M. Scholz, W. Decking, B. Faatz, T. Limberg DESY, Hamburg, Germany B. Liu SINAP, Shanghai, People's Republic of China
	FLASH2 is an extension of the existing FEL FLASH at DESY, Hamburg. It uses the same linear accelerator. A separate tunnel and a new experimental hall will be built next to the existing FLASH facilities. First constructions started in spring 2011. A fast kicker and a septum to be installed behind the last superconducting acceleration module give the possibility to distribute the beam to the existing beam line and to the new extraction arc. Within this arc a pulsed bending magnet allows to send the beam into two separate beam lines: One hosting undulators for SASE and space for HHG seeding (FLASH2), the other serving a proposed plasma wake field experiment or later on another FEL beam line (FLASH3). The extraction arc design has to fulfill specific requirements such as small emittance and energy spread growth. Furthermore, constrains are given by the existing FLASH buildings and by the space required for the in-coupling of the seed laser. Beam quality impairment has been mitigated by designing the beam optics with horizontal beam waists in all bending magnets. To optimize the extraction arc, simulations for different layouts were carried out using the programs ELEGANT and CSRTRACK.

THPB29	Design of a Low Emittance and High Repetition Rate S-band Photoinjector	gun, solenoid, cathode, laser	621
	J.H. Han Diamond, Oxfordshire, United Kingdom
	One of key components for the success of X-ray free-electron lasers (FELs) is the electron injector. Injectors starting with photocathode RF guns provide exceptionally high brightness electron beams and therefore they are being adopted as injectors of X-ray FELs. In this paper we show how to improve the photoinjector performance in terms of emittance and repetition rate by means of components optimization based on mature technologies. Transverse emittance at an injector is reduced by optimizing the RF gun cavity design, gun solenoid position, and accelerating section position. The repetition rate of an injector mainly depends on the cooling capability of the gun cavity. By adopting the coaxial RF gun coupler and improving cooling-water channels of the gun, a maximum repetition rate of 1 kHz for the injector will be achieved.

THPB30	SwissFEL Injector Test Facility – Test and Plans	cathode, gun, cavity, laser	625
	M. Pedrozzi, M. Aiba, S. Bettoni, B. Beutner, A. Falone, R. Ganter, R. Ischebeck, F. Le Pimpec, G.L. Orlandi, E. Prat, S. Reiche, T. Schietinger, A. Trisorio, C. Vicario Paul Scherrer Institut, Villigen, Switzerland
	In August 2010 the Paul Scherrer Institute inaugurated the SwissFEL Injector test facility as a first step toward the Swiss hard X-ray FEL planned at PSI. The main purpose of the facility is to demonstrate and consolidate the generation of high-brightness beam as required to drive the 6 GeV SwissFEL accelerator. Additionally the injector serves as a platform supporting development and test of accelerator components/systems and optimization procedures foreseen for SwissFEL. In this paper we report on the present status of the commissioning with some emphasis on emittance measurements and component performances. The scientific program and long-term plans will be discussed as well.

Paper

Title

Other Keywords

Page

MOPB15

Numerical Simulation of CAEP Compact FEL THz Source

FEL, cavity, simulation, undulator

35

L.J. Chen, Q.K. Jia
USTC/NSRL, Hefei, Anhui, People's Republic of China
M. Li, X. Yang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

Free Election Laser Terahertz source is a good choice for THz source, whose wavelength is tunable. Using 1D FEL stimulation code FELO, we simulate the output characteristic of China Academy of Engineering Physics (CAEP) FEL THz, which is a waveguide FEL oscillator. The beam qualitys’ influence on the operation of FEL, such as energy dispersion, emittance and beam current, have been studied to designate a set of beam parameters. Besides, the output performance of FEL at different output coupling ratio is analyzed. The cavity detuning is discussed too. Meanwhile the influence of the position of the undulator in the cavity on the FEL performance is also studied.

MOPB17

Harmonic Generation for a Hard X-ray FEL

electron, undulator, FEL, bunching

41

Q.R. Marksteiner, K. Bishofberger, B.E. Carlsten, L.D. Duffy, N.A. Yampolsky
LANL, Los Alamos, New Mexico, USA

Funding: We gratefully acknowledge the support of the US Department of Energy through the LANL LDRD Propgram for this work.
The proposed MaRIE XFEL at Los Alamos National Laboratory will generate ¼ Å, longitudinally coherent x-rays with a 20 GeV electron beam. A masked emittance exchanger can be used to generate coherent electron bunching at nm wavelengths. This masked emittance exchanger must be at 1 GeV in the accelerator, in order to mitigate debunching from incoherent synchrotron radiation (ISR). After this, the harmonic content must be stepped up by a factor of 200 in frequency and the electrons must be accelerated to 20 GeV. The nonlinear debunching effects in the accelerator from emittance must be mitigated by keeping the beam transversely large. There are several schemes to step the coherent bunching up to higher harmonics, all which require modulator and dispersive sections [1]. Echo-Enhanced Harmonic Generation, which requires large dispersion, must be incorporated at low energies, where ISR is reduced. Here we compare the usefulness of different harmonic generation schemes, and examine the possibility of placing successive harmonic generation sections at energies lower than 20 GeV in the accelerator line, with the accelerator sections in between used to introduce dispersion to the beam.
[1] Phys. Rev. E 71, 046501 (2005), etc.

MOPB20

Effect of Coulomb Collisions on Echo-Enabled Harmonic Generation (EEHG)

bunching, FEL, scattering, undulator

49

G.V. Stupakov
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. DOE Contract No. DE-AC02-76SF00515.
Echo-enabled harmonic generation (EEHG) for FEL seeding uses two undulator-modulators and two chicanes to introduce a fine structure into the beam longitudinal phase space which, at the end of the system, transforms into high harmonic modulation of the beam current. As a result of this phase space manipulation, after the first chicane, the energy distribution function becomes a rapidly modulated function of energy, with the scale of the modulation of the order of the initial energy spread of the beam divided by the EEHG harmonic number. Small-angle Coulomb collisions between the particles of the beam (also known as intrabeam scattering) tend to smear out this modulation and hence to suppress the beam bunching. In this paper we calculate the EEHG bunching factor with account of the collisions and derive a simple scaling relation for the strength of the effect. Our estimates show that collisions become a limiting factor in EEGH seeding for harmonic numbers roughly exceeding 100.

MOPB30

The Effects of Betatron Motion on the Preservation of FEL Microbunching

electron, betatron, bunching, undulator

81

G. Geloni
European XFEL GmbH, Hamburg, Germany
V. Kocharyan, E. Saldin
DESY, Hamburg, Germany

In some options for circular polarization control at X-ray FELs, a helical radiator is placed a few ten meters distance behind the baseline undulator. If the microbunch structure induced in the baseline (planar) undulator can be preserved, intense coherent radiation is emitted in the helical radiator. The effects of betatron motion on the preservation ofμbunching in such in-line schemes should be accounting for. In this paper we present a comprehensive study of these effects. It is shown that one can work out an analytical expression for the debunching of an electron beam moving in a FODO lattice, strictly valid in the asymptote for a FODO cell much shorter than the betatron function. Further on, numerical studies can be used to demonstrate that the validity of such analytical expression goes beyond the above-mentioned asymptote, and can be used in much more a general context. Finally, a comparison with Genesis simulations is given.

MOPB32

System Trade Analysis for an FEL Facility

FEL, undulator, photon, linac

89

M.W. Reinsch, B. Austin, J.N. Corlett, L.R. Doolittle, G. Penn, D. Prosnitz, J. Qiang, A. Sessler, M. Venturini, J.S. Wurtele
LBNL, Berkeley, California, USA

Designing an FEL from scratch requires the design team to balance multiple science needs, FEL and accelerator physics constraints and engineering limitations. STAFF (System Trade Analysis for an FEL Facility) enables the user to rapidly explore a large range of Linac and FEL design options. The model utilzes analytical models such as the Ming Xie formulas when appropriate and look-up tables when necessary to maintain speed, flexibility and extensiblity. STAFF allows for physics models for FEL harmonics, wake fields, cavity higher-order modes and aspects of linac particle dynamics. The code will permit the user to study error tolerances and multiple beamlines so as to explore the full capabilities of an entire user facility. This makes it possible to optimize the integrated system in terms of performance metrics such as photons/pulse, photons/sec and tunability range while ensuring that unrealistic requirements are not put on either the electron beam quality, undulator field/gap requirements or other system elements. This paper will describe preliminary results from STAFF as applied to a CW FEL soft X-ray facility.

MOPC06

X-Ray FELs Based on ERL Facilities

FEL, radiation, undulator, electron

111

A. Meseck
HZB, Berlin, Germany
G.H. Hoffstaetter, F. Löhl, C.E. Mayes
CLASSE, Ithaca, New York, USA

The characteristic high repetition rate and the high spectral brightness of the electron beams delivered by ERLs have led to a large number of ERL based proposals for hard X-ray sources including X-ray FELs. FEL oscillators, including those proposed for hard X-rays, require comparatively low peak currents and are particularly suitable for ERLs. However single-pass FELs in SASE or seeded mode do not seem out of reach when bunch-compression schemes for higher peak currents are utilized. Using the proposed Cornell ERL as an example, we present and discuss oscillator and single-pass FEL schemes which provide extremely high spectral-brightness ultra-short X-ray pulses for experiments.

MOPC12

Coherent Synchrotron Radiation and Bunch Compression Studies in the Emittance Exchange Beamline at the Fermilab A0 Photoinjector

radiation, polarization, cavity, synchrotron

121

J.C.T. Thangaraj, M.D. Church, H.T. Edwards, A.S. Johnson, A.H. Lumpkin, J. Ruan, J.K. Santucci, Y.-E. Sun, R.M. Thurman-Keup
Fermilab, Batavia, USA
T.J. Maxwell, P. Piot
Northern Illinois University, DeKalb, Illinois, USA

One of goals of the Fermilab A0 photoinjector is to investigate experimentally the transverse to longitudinal emittance exchange principle. Coherent synchrotron radiation in the emittance exchange line could limit short pulse operation of the emittance exchanger. In this paper, we present experimental and simulation study of the coherent synchroton radiation (CSR) in the emittance exchange line at A0 photoinjector. We also show how EEX can be used to compress a bunch by adding chirp to the incoming beam.

MOPC14

Infrared Single Spike Pulses Generation Using a Short Period Superconducting Tape Undulator at APEX

undulator, FEL, space-charge, electron

129

D. Filippetto, C. F. Papadopoulos, G. Penn, S. Prestemon, F. Sannibale
LBNL, Berkeley, California, USA
C. Pellegrini
UCLA, Los Angeles, California, USA
M. Yoon
POSTECH, Pohang, Kyungbuk, Republic of Korea

Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
We report on the possibility of constructing an infrared FEL by combining a novel design super-conducting undulator developed at LBNL with the high brightness beam from the APEX injector facility at the Lawrence Berkeley National Laboratory. Calculations show that the resulting FEL is expected to deliver a saturated power of about a MW within a 4 m undulator length when operating in Self-Amplified-Spontaneus-Emission mode, with a single-spike of coherent radiation at 2 μm wavelength. The sub-cm undulator periods, associated with the relatively low energy of the APEX beam (20-25 MeV), forces the FEL to operate in a regime with unusual and interesting characteristics. The alternative option of laser seeding the FEL is also examined, showing the potential to reduce the saturation length even further.

TUOBI3

Operational Experience at LCLS

undulator, linac, electron, FEL

166

H. Loos
SLAC, Menlo Park, California, USA

Funding: *Work supported by DOE contract DE-AC02-76SF00515
The Linac Coherent Light Source (LCLS) X-ray FEL has been operational since 2009 and is delivering soft and hard x-rays to users now in the 4th user run. Reliable operation to deliver x-rays to users, quick machine turn on after shutdowns, and fast configuration changes for the wide range of user requests are particularly important for a facility serving a single user at a time. This talk will discuss procedures to set-up and optimize the accelerator and FEL x-ray beam for user operation. The emphasis will be on the most relevant diagnostics and tuning elements as well as the experience with feedback systems and high level support software to automate FEL operation.

Slides TUOBI3 [3.074 MB]

TUOC3

High QE, Low Emittance, Green Sensitive FEL Photocathodes Using K₂CsSb

electron, laser, cathode, gun

179

H.A. Padmore, D. Dowell, J. Feng, T. Vecchione, W. Wan
LBNL, Berkeley, California, USA
I. Ben-Zvi
Stony Brook University, Stony Brook, USA
T. Rao, J. Smedley
BNL, Upton, Long Island, New York, USA

Funding: Work was supported by the Director, Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231, KC0407-ALSJNT-I0013, and DE-SC0005713.
We describe the development of photocathodes based on Potassium-Cesium-Antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light and low transverse emittance. We have demonstrated QE of 7% at 532 nm, a normalized transverse emittance of 0.36 μm at 543 nm and 3 MV/m field gradient[1]. We have also shown that the material can be relatively robust to residual water contamination and we have extracted current densities of 1 mA/mm² with very long lifetime. We believe that this work is an important step forward in FEL development where high repetition rate is required.
[1] Applied Physics Letters (submitted)

Slides TUOC3 [4.825 MB]

TUPA15

Status of the SwissFEL Facility at the Paul Scherrer Institute

FEL, undulator, linac, electron

223

S. Reiche
Paul Scherrer Institut, Villigen, Switzerland

SwissFEL is a X-ray Free-electron Laser facility with a soft and hard X-ray beamline, planned to be built at the Paul Scherrer Institute and to be finished in 2016. It covers the wavelength range from 1 Angstrom to 7 nm. In addition to the SASE operation at the entire wavelength, seeding is foreseen down to a wavelength of 1 nm. We report in this presentation the status of the SwissFEL facility, including the layout, the timeline of the project, the different operation modes and the expected performance of the FEL beamlines.

TUPA18

Considerations about Optics-Based Phase-Space Measurements at Linac-Based FEL Facilities

optics, quadrupole, lattice, diagnostics

231

B. Beutner, E. Prat
Paul Scherrer Institut, Villigen, Switzerland

Transverse phase-space measurements are an essential issue for FEL facilities. After acceleration in the injector the energy is sufficiently high to bring the beam out of the space-charge dominated regime, thus optics based techniques are favored. The beam moments at a given point in the machine are fitted to beam size values downstream with different phase advances between the reconstruction and the measurement point. Two principle methods are possible. Beam sizes can be measured at different positions in the beam line keeping the lattice unchanged. The other possibility is to actively change quadrupoles and use only one screen. These two techniques are compared in this paper including monte-carlo studies on systematic errors using the SwissFEL Injector Test Facility as an example. On the other hand beam size measurements, which are done with OTR screens at SwissFEL Injector Test Facility, are critical for such measurements. An analysis of these images can be an issue, especially if the signal-to-noise is compromised for example by low bunch charges. This study on the phase-space measurement techniques will be completed by a discussion of the image post-processing procedures.

TUPA25

EEHG Seeding Design for SwissFEL

bunching, laser, electron, FEL

251

E. Prat, S. Reiche
Paul Scherrer Institut, Villigen, Switzerland

The SwissFEL facility, planned at the Paul Scherrer Institute, is based on the SASE operation of a hard (1-7 Å) and a soft (7-70 Å) X-ray FEL beamline. In addition, seeding is foreseen for the soft X-ray beamline, down to a wavelength of 1 nm. The Echo-Enabled Harmonic Generation (EEHG) scheme, which utilizes a rather complex manipulation of the longitudinal phase space distribution of the electron beam to generate high harmonic density modulation, is presently considered the first choice for seeding at SwissFEL. However, EEHG is highly demanding and complex at 1 nm, therefore other strategies like High-Harmonic Generation (HHG) and self-seeding are also evaluated. This paper presents the current status of the seeding design for SwissFEL based on EEHG.

TUPA31

Transverse Phase-space Studies for the Electron Optics at the Direct XUV-seeding Experiment at FLASH (DESY)

undulator, electron, simulation, diagnostics

263

S. Ackermann, V. Miltchev, J. Roßbach
Uni HH, Hamburg, Germany

Funding: BMBF under contract No. 05 ES7GU1 - DFG GrK 1355 - Joachim Herz Stiftung
During the shutdown in 2009/2010 the Free-Electron Laser in Hamburg (FLASH) was upgraded with an experiment to study the high-gain-FEL amplification of a laser ‘‘seed'' from a high harmonic generation (HHG) source in the XUV wavelength range-sFLASH. For an optimal FEL-performance knowledge of the electron bunch transverse phase-space as well as control on the electron optics parameters is required. In this contribution the technical design, the present status and the commissioning results of the sFLASH diagnostic stations will be presented. The possible options for transverse phase space characterization will be discussed. An emphasis will be put on the error analysis and the tolerance estimations. Analysis of experimental data from both OTR-screens and wire scanners will be presented and discussed.

TUPB12

Combined Optimization of a Linac-based FEL Light Source Using a Multiobjective Genetic Algorithm

linac, FEL, electron, cavity

283

C. F. Papadopoulos, D. Filippetto, G. Penn, J. Qiang, F. Sannibale, M. Venturini
LBNL, Berkeley, California, USA

Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
We report on the development status and preliminary results of a combined optimization scheme for a linac-based, high repetition rate, soft X-ray FEL. The underlying model includes the injector and linac parts of the machine, and the scheme will integrate the design process of these components toward the optimization of the FEL performance. For this, a parallel, multi-objective genetic algorithm is used. We also discuss the beam dynamics considerations that lead to the choices of objectives, or figure-of-merit beam parameters, and describe numerical solutions compatible with the requirements of a high repetition rate user facility.

TUPB13

Beam Dynamics Considerations for APEX a High Repetition Rate Photoinjector

FEL, gun, electron, space-charge

287

C. F. Papadopoulos, D. Filippetto, F. Sannibale, R.P. Wells
LBNL, Berkeley, California, USA

Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The Advanced Photoinjector EXperiment is a photo-injector project at Lawrence Berkeley National Lab, designed to test the performance of a high repetition rate (>1 MHz) VHF normal conducting electron gun. The requirements of high beam brightness, as well as significant compression at low energy determine the base setup for the injector transport line. The beam dynamics considerations for a high repetition rate injector are discussed and the potential to use multiple bunch charges that require different tunings of the base setup is explored.

TUPB19

Design and Beam Dynamics Simulation for the Photoinjector of Shanghai Soft X-ray Free Electron Laser Test Facility

laser, gun, linac, simulation

299

W.-H. Huang, Q. Du, Y.-C. Du, H.J. Qian, C.-X. Tang, L.X. Yan
TUB, Beijing, People's Republic of China

The Shanghai soft X-ray free electron laser test facility (SXFEL) aims to radiate at 9 nm based on the cascaded high-gain harmonic-generation (HGHG) scheme. The photoinjector of SXFEL consists of Ti-sapphire driving laser system, S-band photocathode RF gun, booster linacs, laser heater, beam diagnostics and matching section. It will produce ~130 MeV electron beam in high charge regime (~0.5 nC) with a baseline transverse emittance of 1.5 mm-mrad. This paper will present basic designs and beam dynamics simulations of SXFEL photoinjector.

TUPB28

Considerations for a Light Source Test Facility at Daresbury Laboratory

undulator, electron, FEL, laser

308

N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
J.A. Clarke, D.J. Dunning, J.W. McKenzie
Cockcroft Institute, Warrington, Cheshire, United Kingdom

This paper considers design options for a dedicated light source test facility at Daresbury Laboratory in the United Kingdom. The facility layout should be easily configurable to enable exploration of many research themes including: ultrashort pulse generation; seeding and harmonic generation; direct laser/electron beam interactions; compact FELs; high brightness photoinjectors. The strategy is to develop and demonstrate novel concepts and expertise relevant to future generations of FEL-based light sources, significantly shortening the R&D phase of any future light source in the UK.

WEPA01

Commissioning of a Photoinjector in HLS

laser, cathode, solenoid, gun

331

Z.G. He, Q.K. Jia, B.G. Sun, X.H. Wang
USTC/NSRL, Hefei, Anhui, People's Republic of China

A BNL type photoinjector was installed in HLS (Hefei Light Source) and commissioning work was carrying out in last months. The dark current was measured when the high power testing of the gun was processed. The quantum efficiency (QE) of the photocathode was measured and studied, the main parameters of beam quality such as electric charge, transverse emittance and energy were measured and presented in this paper.

WEPA06

Experimental Studies with Spatial Gaussian-cut Laser for the LCLS Photocathode Gun

laser, simulation, cathode, electron

341

F. Zhou, A. Brachmann, P. Emma, A. Gilevich, Z. Huang
SLAC, Menlo Park, California, USA

Funding: U.S. Department of Energy under contract DE-AC02-76SF00515
To further enhance the LCLS injector performances or simplify its operating conditions, we are evaluating the various parameters including the photocathode drive laser. Simulations show that both the projected and time-sliced emittances with spatial Gaussian profiles having reasonable tail-cutoff are better than those with uniform one. The simulated results are also supported by theoretical analyses. In the LCLS, the spatial uniform or quasi-Gaussian laser profiles are conveniently obtained by adjusting the optics of telescope upstream of an iris, used to define laser size on the cathode. Preliminary beam studies at the LCLS show that both the projected and time-sliced emittances with spatial quasi-Gaussian laser are almost as good as, although not better than, those with uniform one, and also laser transmission through the iris with the quasi-Gaussian is twice that with uniform one, which is to ease copper cathode operations and thus improve the LCLS operation efficiency. More beam studies are planned in the coming summer to measure FEL performances with the quasi-Gaussian in comparison with the uniform one. All simulations and measurements are presented.

WEPA21

Research of Emittance Compensation of CAEP CW DC-Gun Photoinjector

solenoid, gun, space-charge, electron

377

P. Li, M. Li, D. Wu, Z. Xu, X. Yang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

Emittance growth is very import for photo-cathode injector due to space charge effect. The emittance compensation technology will be used on the 350 kV photo-cathode DC gun for the CAEP CW FEL, where the energy of electron beam is extremely low and Emittance growth is great severity. In this paper, the space charge force and its effect on electron beam transverse emittance is discussed, the principle of emittance compensation in phase space is analyzed. And a solenoid for emittance compensation is designed. Its beam dynamics has been studied by the PARMELA code. Simulation results indicate that the normalized transverse RMS emittance for electron beam of 80 pC is 1.267 mm•mrad with σ_r=1.5 mm, σ_z=4.25 pS.

WEPB15

Reversible Electron Beam Heater for Suppression of Microbunching Instabilities Based on Transverse Deflecting Cavities

linac, FEL, simulation, laser

409

C. Behrens
DESY, Hamburg, Germany
Z. Huang, D. Xiang
SLAC, Menlo Park, California, USA

The presence of the microbunching instability due to the compression of high-brightness electron beams at existing and future X-ray free-electron lasers (FEL) results in restrictions on the attainable lasing performance and renders diagnostics like beam imaging with optical transition radiation impossible. The instability can be suppressed by introducing additional energy spread, i.e. heating the beam, as demonstrated by the successful operation of the laser heater system at the Linac Coherent Light Source. The increased energy spread is typically tolerable for self-amplified spontaneous emission FELs but limits the effectiveness of seeded FELs. In this paper, we present a reversible electron beam heating system based on two transverse deflecting cavities (TCAV) in front and behind a bunch compressor chicane. The additional energy spread will be introduced in the first TCAV, which suppresses the microbunching instability, and then will be eliminated in the second TCAV. We show the feasibility of the suppression of microbunching instabilities based on calculations and simulations, and set limits to the acceptable jitter tolerances.

WEPB20

The Design Of A Multi-Beam Electron Gun For A Photonic Free-Electron Laser

gun, cathode, electron, beam-transport

427

J.H.H. Lee, K.-J. Boller, T. Denis, P.J.M. van der Slot
Mesa+, Enschede, The Netherlands

Funding: This research is supported by the Dutch Technology Foundation STW, applied science division of NWO and the Technology Program of the Ministry of Economic Affairs.
The photonic Free-Electron Laser (pFEL) is a novel slow-wave device which relies on a photonic crystal (PhC) to synchronize the Cherenkov electromagnetic radiation generated from the co-propagating electron beams. The advantage of pFEL is in its frequency- and power-scaling properties. The scale invariance of Maxwell’s equations allows the use of the same beam energy to operate at higher frequencies when the PhC is correspondingly scaled. On the other hand, power-scaling is achieved by varying the number of electron beams propagating in parallel through the PhC. To produce a set of parallel beams, we have designed a multi-beam electron gun using flat cathodes, which produces a total current of 1 A at a beam voltage of 14 kV. We will present the design of this gun together with the expected performance. In addition, we have investigated the beam transport system and will discuss the options for guiding the beams through the PhC.

THOA3

Demonstration of Transverse-to-longitudinal Emittance Exchange at A0 Photoinjector

cavity, space-charge, radiation, booster

443

J. Ruan, A.S. Johnson, A.H. Lumpkin, Y.-E. Sun, R.M. Thurman-Keup
Fermilab, Batavia, USA

The 3-D phase-space manipulation of electron beams enhances the performance of next generation accelerators including high energy colliders and accelerator based light sources. In this paper we will report an observation of near ideal transverse to longitudinal emittance exchange at the Fermilab A0 Photoinjector. The emittance exchange (EEX) beamline consists a 3.9 GHz normal conducting deflecting mode cavity positioned between two magnetic doglegs. We will also compare the experiment results to simulations.

THOA4

Three Bunch Compressor Scheme for SASE FEL

linac, FEL, undulator, electron

447

H.-S. Kang, I.S. Ko, S.H. Nam
PAL, Pohang, Kyungbuk, Republic of Korea
M.-H. Cho, C.H. Yi
POSTECH, Pohang, Kyungbuk, Republic of Korea

The bend angle of dipoles in bunch compressor needs to be small enough to reduce the emittance increase due to CSR, which requires a larger energy chirp at the preceding RF linac. Correlated energy spread is not reduced below FEL parameter after the following RF linac because of the small number of accelerating sections as in the PAL XFEL design. Three bunch compressor scheme can make it possible to minimize the CSR induced emittnace growth as well as reduce the correlated energy spread below FEL parameter.

Slides THOA4 [1.467 MB]

THOB2

Advanced Beam Dynamics Experiments at SPARC

gun, radiation, laser, electron

451

A. Bacci, D. Alesini, M. Bellaveglia, M. Castellano, E. Chiadroni, G. Di Pirro, A. Drago, M. Ferrario, A. Gallo, G. Gatti, A. Ghigo, E. Pace, A.R. Rossi, C. Vaccarezza
INFN/LNF, Frascati (Roma), Italy
A. Cianchi
Università di Roma II Tor Vergata, Roma, Italy
M. Del Franco, L. Giannessi, A. Petralia, M. Quattromini, C. Ronsivalle, V. Surrenti
ENEA C.R. Frascati, Frascati (Roma), Italy
S. Lupi
Coherentia, Naples, Italy
B. Marchetti
INFN-Roma II, Roma, Italy
A. Mostacci, L. Palumbo
Rome University La Sapienza, Roma, Italy
V. Petrillo
Universita' degli Studi di Milano, Milano, Italy
L. Serafini
Istituto Nazionale di Fisica Nucleare, Milano, Italy
M. Serluca
INFN-Roma, Roma, Italy

The successful operation of the SPARC injector in the Velocity Bunching (VB) mode (bunches with 1 kA current with emittance of 3 mm-mrad have been produced) has opened new perspectives to conduct advanced beam dynamics experiments with ultra-short electron pulses able to extend the THz spectrum or to drive the FEL in the SASE Single Spike mode. A new technique called Laser Comb, able to generate a train of short pulses with high repetition rate, has been extensively tested in the VB configuration. Two electron beam pulses 300 fs long separated by 1 ps have been characterized and the spectrum produced by the SASE interaction has been observed, showing that both pulses have been correctly matched to the undulator and were both lasing. In this paper we report the experimental and theoretical results obtained so far.

Slides THOB2 [6.673 MB]

THPA02

Two-dimensional Effects on the Behavior of the CSR Force In a Bunch Compression Chicane

electron, FEL, optics, dipole

469

R. Li, R.A. Legg, B. Terzić
JLAB, Newport News, Virginia, USA
J. Bisognano, R.A. Bosch
UW-Madison/SRC, Madison, Wisconsin, USA

Funding: This work was supported by U.S. DOE under Contract No. DE-AC05-06OR23177.
The endeavor to reach higher brightness of electron bunches in the design of future FEL is seriously challenged by the CSR effect in magnetic bends. Extensive studies on the CSR effects have shown that the 1D approximation of the CSR force is valid for a wide parameter regime. However, as the bunch gets increasingly compressed in the compression process, the behavior of the CSR interaction force will be influenced by the evolution of the 2D bunch distribution. Here we explore this 2D effect using semi-analytical and numerical study of the retarded potentials for an evolving 4D Gaussian phase space distribution with initial energy chirp. We will present results of our systematic exploration of this two-dimensional effect. We will display the interesting dependence of the 2D CSR force on the initial horizontal emittance and uncorrelated energy spread around minimum bunch length, and show the comparison of these results with their 1D counterpart. Physical interpretation will also be discussed.

THPA06

Emittance for Different Bunch Charges at the Upgraded PITZ Facility

gun, laser, booster, cavity

473

S. Rimjaem, G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, A. Shapovalov, F. Stephan, G. Vashchenko, S. Weidinger
DESY Zeuthen, Zeuthen, Germany
M. Hoffmann, H. Schlarb
DESY, Hamburg, Germany
M.A. Nozdrin
JINR, Dubna, Moscow Region, Russia
D. Richter
HZB, Berlin, Germany
I.H. Templin, I. Will
MBI, Berlin, Germany

Optimizations of electron sources for short-wavelength Free Electron Laser (FELs) at the Photo Injector Test facility at DESY, location Zeuthen (PITZ) have been continued with a new radio frequency (RF) gun cavity, a new post-accelerating Cut Disk Structure (CDS) booster cavity and several upgraded diagnostic components. The new booster cavity allows stable operation with higher acceleration and longer pulse trains than the operation with the previous TESLA type cavity. Electron beams with a maximum mean momentum of about 25 MeV/c can be produced with the setup described in this paper. Together with the upgraded RF system for the gun and the new CDS booster cavity, the electron beam stability was significantly improved. A large fraction of the measurement program in 2010-2011was devoted to study the dependence of the transverse projected emittance on the bunch charge. Measurement results using this upgraded facility are reported and discussed.

THPA08

An Option of High Charge Operation for the European XFEL

electron, laser, FEL, gun

481

M. Krasilnikov, H.-J. Grabosch, M. Groß, L. Hakobyan, Ye. Ivanisenko, G. Klemz, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, S. Rimjaem, F. Stephan, G. Vashchenko, S. Weidinger
DESY Zeuthen, Zeuthen, Germany
G. Asova
INRNE, Sofia, Bulgaria
I.I. Isaev, A. Shapovalov
MEPhI, Moscow, Russia
M.A. Khojoyan
ANSL, Yerevan, Armenia
D. Richter
HZB, Berlin, Germany
E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany
I.H. Templin, I. Will
MBI, Berlin, Germany

The 1.3 GHz superconducting accelerator developed in the framework of TESLA and the European XFEL project holds potential to accelerate high charge electron beams. This feature has been successfully demonstrated during the first run of the free electron laser at the TESLA Test Facility with lasing driven by electron bunches with a charge of up to 4 nC. Currently DESY and the European XFEL GmbH perform revision of the baseline parameters for the electron beam. In this report we discuss a potential option of operation of the European XFEL driven by high charge (1 nC to 3 nC) electron beams. We present the results of the production and characterization of high charge electron bunches. Experiments have been performed at PITZ and demonstrated good properties of the electron beam in terms of emittance. Simulations of the radiation properties of SASE FELs show that application of high charge electron beams will open up the possibility to generate radiation pulse energies up to a few hundred milli-Joule level.

THPA15

Simulation Studies of Generating Ultra Short Pulses at PITZ

laser, electron, simulation, cathode

499

M.A. Khojoyan, M. Krasilnikov, A. Oppelt, F. Stephan
DESY Zeuthen, Zeuthen, Germany
M.A. Khojoyan
ANSL, Yerevan, Armenia

Generation of the ultra short electron bunches (<10fs bunch length) which have a small transverse phase space volume and relatively small energy spread is of great interest. Such bunches are required for fully coherent (transversally and longitudinally) FEL radiation (single spike lasing) and for plasma acceleration experiments. The Photo Injector Test Facility at DESY in Zeuthen has already demonstrated the possibility to generate and characterize high quality electron beams for a wide range of bunch charges. Currently electron bunches have a typical length of several ps. To study the possibility of producing short electron bunches at PITZ many beam dynamics simulations have been performed for 1pC bunch charge using the ASTRA code. The current PITZ beam line is supposed to be extended by a small magnet chicane. Several temporal profiles of the cathode laser pulse have been used for the simulations to produce ultra-short electron bunches with small transverse sizes. The results of the beam dynamics simulations are presented and discussed.

THPA23

Investigations on Thermal Emittance at PITZ

laser, electron, cathode, simulation

519

M. Otevřel, G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, B. Petrosyan, D. Richter, S. Rimjaem, A. Shapovalov, F. Stephan, G. Vashchenko, S. Weidinger
DESY Zeuthen, Zeuthen, Germany
S. Lederer
DESY, Hamburg, Germany

The main aim of the Photo-Injector Test Facility at DESY, location Zeuthen (PITZ) is to develop and test an FEL photo-injector system capable of producing high charge electron bunches of lowest possible transverse emittance, which has a fundamental impact on FEL performance. Recent measurement results at PITZ showed a fairly small electron beam transverse projected emittance [1] which increased interest in the thermal emittance and its contribution to the overall electron beam emittance budget. Therefore thermal emittance was investigated at PITZ. Results of these studies are presented and discussed.

THPA30

First Results with Tomographic Reconstruction of the Transverse Phase Space at PITZ

laser, booster, cathode, gun

543

G. Asova, H.-J. Grabosch, M. Groß, L. Hakobyan, I.I. Isaev, Ye. Ivanisenko, M.A. Khojoyan, G. Klemz, M. Krasilnikov, M. Mahgoub, D. Malyutin, A. Oppelt, M. Otevřel, B. Petrosyan, S. Rimjaem, F. Stephan, G. Vashchenko
DESY Zeuthen, Zeuthen, Germany
G. Asova
INRNE, Sofia, Bulgaria
D. Richter
HZB, Berlin, Germany

The development of high brightness electron sources capable to drive FELs like FLASH and European XFEL is a major objective of the Photo-Injector Test Facility at DESY in Zeuthen, PITZ. A key parameter used to define the beam quality at PITZ is the transverse phase-space density distribution and its evolution along the beamline. Complementary to the standard phase-space measurement setup constituting slit-scan stations, a module for tomographic diagnostics has been commissioned in 2010/2011. It consists of four observation screens separated by FODO cells and an upstream matching section. The expected advantages of the tomography method are the possibility to measure both transverse planes simultaneously and an improved resolution for low charges and short pulse trains. The fundamental challenges are related to strong space-charge forces at low beam momentum of only 25~MeV/c at PITZ at the moment. Such a constraint presents an obstacle to obtain beam envelope parameters well-matched to the optics of the FODO lattice. This contribution presents the first practical experience with the phase-space tomography module.

THPB02

Implementation of 2D-emittance Compensation Scheme in the BERLinPro Injector

space-charge, booster, linac, solenoid

564

A.V. Bondarenko, A.N. Matveenko
HZB, Berlin, Germany

Helmholtz-Zentrum Berlin officially started Jan. 2011 the design and construction of the Berlin Energy Recovery Linac Project BERLinPro. The initial goal of this compact ERL is to develop the ERL accelerator physics and technology required to accelerate a high-current (100 mA) low emittance beam (1 mm•mrad normalized), as required for future ERL-based synchrotron light sources. High power ERL based FELs demand low emittance, high peak and average current beams. The injection energy in an ERL is usually rather low to decrease power consumption and avoid activation of the beam dump. Therefore, the space charge is the main reason of the emittance degradation in the injector. The implementation of an emittance compensation scheme in the injector is necessary to achieve a low emittance. Since injector’s optics is axially non-symmetric, the 2D-emittance compensation scheme [1] should be used. The implementation of the 2D-emittance compensation scheme at BERLinPro injector is presented in this contribution. Other sources of emittance growth in ERL injectors are also discussed.
[1] S.V. Miginsky, "Emittance compensation of elliptical beam", NIM A 603 (2009), pp 32-34.

THPB15

Metal Cathodes with Reduced Emittance and Enhanced Quantum Efficiency

cathode, FEL, electron, photon

586

C.M.R. Greaves, J. Feng, H.A. Padmore, W. Wan
LBNL, Berkeley, California, USA
D. Dowell
AES, Princeton, New Jersey, USA

In this paper, we report experimental results on photoemission from copper and silver surfaces. Using the technique of angle resolved photoemission spectroscopy (ARPES), we demonstrate that, for excess energy around 0.5 eV, the photoelectrons from the Cu(111) and Ag(111) surfaces generated by p-polarized light originate primarily from the well-known surface state with normalized emittance only a fraction of that of the polycrystalline copper cathode presently used in the RF guns. Meanwhile, we demonstrate that the enhancement of the quantum efficiency (QE) at grazing angle is closely related to the surface state as well. Furthermore, we show that the surface state can be easily restored by a simple anneal process, thus pointing to a practical way to reducing the emittance and QE of a metal cathode simultaniously.

THPB19

Investigations of OTR Polarization Effects in Beam-profile Monitors

polarization, optics, radiation, electron

594

A.H. Lumpkin, A.S. Johnson, J. Ruan, R.M. Thurman-Keup
Fermilab, Batavia, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
The characterization of transverse beam size using optical transition radiation (OTR) imaging is a well-established technique at many accelerators including the Fermilab A0 photoinjector (A0PI) facility. However, there is growing empirical evidence that the utilization of the polarization component orthogonal to the dimension of interest results in a smaller observed projected image profile. We have continued investigations of this phenomenon with a more controlled experiment where the linear polarizers are selectable in a filter wheel which also included a blank glass position to compensate for the optical path. The aperture for light collection is thus kept fixed compared to our previous tests. We also have balanced the digital camera gain to present similar signal levels to the data analysis program for both the total OTR and the polarized components. At the relatively low Lorentz factor (gamma) of 30, we observed 10-15% projected profile size reductions on a 65-micron beam size case with the perpendicularly polarized components. This anomalous effect in magnitude is compared to results from a standard OTR point-spread-function model.

THPB21

Extraction Arc for FLASH2

extraction, simulation, septum, electron

601

M. Scholz, W. Decking, B. Faatz, T. Limberg
DESY, Hamburg, Germany
B. Liu
SINAP, Shanghai, People's Republic of China

FLASH2 is an extension of the existing FEL FLASH at DESY, Hamburg. It uses the same linear accelerator. A separate tunnel and a new experimental hall will be built next to the existing FLASH facilities. First constructions started in spring 2011. A fast kicker and a septum to be installed behind the last superconducting acceleration module give the possibility to distribute the beam to the existing beam line and to the new extraction arc. Within this arc a pulsed bending magnet allows to send the beam into two separate beam lines: One hosting undulators for SASE and space for HHG seeding (FLASH2), the other serving a proposed plasma wake field experiment or later on another FEL beam line (FLASH3). The extraction arc design has to fulfill specific requirements such as small emittance and energy spread growth. Furthermore, constrains are given by the existing FLASH buildings and by the space required for the in-coupling of the seed laser. Beam quality impairment has been mitigated by designing the beam optics with horizontal beam waists in all bending magnets. To optimize the extraction arc, simulations for different layouts were carried out using the programs ELEGANT and CSRTRACK.

THPB29

Design of a Low Emittance and High Repetition Rate S-band Photoinjector

gun, solenoid, cathode, laser

621

J.H. Han
Diamond, Oxfordshire, United Kingdom

One of key components for the success of X-ray free-electron lasers (FELs) is the electron injector. Injectors starting with photocathode RF guns provide exceptionally high brightness electron beams and therefore they are being adopted as injectors of X-ray FELs. In this paper we show how to improve the photoinjector performance in terms of emittance and repetition rate by means of components optimization based on mature technologies. Transverse emittance at an injector is reduced by optimizing the RF gun cavity design, gun solenoid position, and accelerating section position. The repetition rate of an injector mainly depends on the cooling capability of the gun cavity. By adopting the coaxial RF gun coupler and improving cooling-water channels of the gun, a maximum repetition rate of 1 kHz for the injector will be achieved.

THPB30

SwissFEL Injector Test Facility – Test and Plans

cathode, gun, cavity, laser

625

M. Pedrozzi, M. Aiba, S. Bettoni, B. Beutner, A. Falone, R. Ganter, R. Ischebeck, F. Le Pimpec, G.L. Orlandi, E. Prat, S. Reiche, T. Schietinger, A. Trisorio, C. Vicario
Paul Scherrer Institut, Villigen, Switzerland

In August 2010 the Paul Scherrer Institute inaugurated the SwissFEL Injector test facility as a first step toward the Swiss hard X-ray FEL planned at PSI. The main purpose of the facility is to demonstrate and consolidate the generation of high-brightness beam as required to drive the 6 GeV SwissFEL accelerator. Additionally the injector serves as a platform supporting development and test of accelerator components/systems and optimization procedures foreseen for SwissFEL. In this paper we report on the present status of the commissioning with some emphasis on emittance measurements and component performances. The scientific program and long-term plans will be discussed as well.