PAC07 - Classification:02 Synchrotron Light Sources and FELs/A06 Free Electron Lasers

02 Synchrotron Light Sources and FELs

A06 Free Electron Lasers

Paper	Title	Page
MOOAAB02	Experimental Results with the SPARC Emittance-meter	80
	M. Ferrario D. Alesini, M. Bellaveglia, S. Bertolucci, R. Boni, M. Boscolo, M. Castellano, A. Clozza, L. Cultrera, G. Di Pirro, A. Drago, A. Esposito, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, A. Ghigo, M. Incurvati, C. Ligi, M. Migliorati, A. Mostacci, E. Pace, L. Palumbo, L. Pellegrino, R. Ricci, C. Sanelli, M. Serio, F. Sgamma, B. Spataro, F. Tazzioli, S. Tomassini, C. Vaccarezza, M. Vescovi, C. Vicario INFN/LNF, Frascati (Roma) A. Bacci, S. Cialdi, A. R. Rossi, L. Serafini INFN-Milano, Milano L. Catani, E. Chiadroni, A. Cianchi INFN-Roma II, Roma A. M. Cook, M. P. Dunning, P. Frigola, J. B. Rosenzweig UCLA, Los Angeles, California L. Giannessi, M. Quattromini, C. Ronsivalle ENEA C. R. Frascati, Frascati (Roma) P. Musumeci, M. Petrarca INFN-Roma, Roma
	The SPARC project foresees the realization of a high brightness photo-injector to produce a 150-200 MeV electron beam to drive a SASE-FEL in the visible light. As a first stage of the commissioning a complete characterization of the photoinjector has been done with a detailed study of the emittance compensation process downstream the gun-solenoid system. For this purpose a novel beam diagnostic device, called emittance meter, has been developed and used at SPARC. This device has allowed to measure the evolution of beam sizes, energy spread and rms transverse emittances at different location along the beamline, in the region where space-charge effects dominate the electron dynamics and the emittance compensation process takes place. In this paper we report our commissioning experience and the results obtained. In particular a comparison between the performances of a Gaussian laser pulse versus a Flat Top laser pulse will be discussed. We report also the first experimental observation of the double emittance minima effect on which is based the optimised matching with the SPARC linac.
	Slides
MOZBAB01	Review of the Worldwide SASE FEL Development	89
	T. Shintake
	Talk will review the worldwide efforts towards VUV and X-ray SASE FELs,including low emittance electron source, linear accelerator, bunch compressor, undulator, beam diagnostics, alignment, and control, facility building and seeding technology.
	Slides
MOZBAB02	Short Wavelength SASE FEL: Experiment vs. Theory	94
	J. Rossbach
	Since 2005, the Free-Electron Laser FLASH at DESY delivers radiation pulses with unprecedented parameters to scientific users. Pulses in the 10 femtosecond range are produced at record wavelengths as short as 13 nanometers. Operating in the FEL saturation regime at the Gigawatt level, even higher harmonics are generated that are powerful enough to be attractive for users. Radiation pulses and the properties of electron bunches have been characterized in quite some detail. Based on these results, the state of the art of detailed comparison between the theory and experiment of short wavelength SASE FELs will be presented.
	Slides
MOZBAB03	Compact Long Wavelength Free-Electron Lasers	99
	H. L. Andrews C. H. Boulware, C. A. Brau, J. D. Jarvis Vanderbilt University, Nashville, Tennessee
	The idea of using the Smith-Purcell effect to build a compact (table-top) long wavelength (0.1 -1 mm) free-electron laser is quite old. However, it is only recently that a complete theory for the operation of such devices has been proposed. The current state of the theoretical and experimental efforts to understand these devices will be summarized.
	Slides
MOOBAB01	Time-Resolved Phase Space Tomography at Flash Using a Transverse Deflecting RF-Structure	104
	M. Roehrs C. Gerth, H. Schlarb DESY, Hamburg
	To initiate Self-Amplification of Spontaneous Emission (SASE) in single-pass Free Electron Lasers (FEL), electron bunches with high peak current and small slice emittance and energy spread are necessary. At FLASH at DESY, this is accomplished by longitudinal bunch compression in two magnetic chicanes. The compression process may be accompanied by distortions from coherent synchrotron radiation and space charge forces. Their effect on the bunch properties can be studied with a vertically deflecting rf-structure (LOLA), which allows to measure the longitudinal phase space distribution and horizontal slice emittance of single bunches. In combination with tomographic methods the horizontal phase space distribution of time slices can be reconstructed. In this paper measurement results for SASE operation are presented and compared to simulations and bunch properties infered from the radiation signal.
	Slides
TUPMN012	STARS - A Two-Stage High-Gain Harmonic Generation FEL Demonstrator	938
	T. Kamps M. Abo-Bakr, W. Anders, J. Bahrdt, P. Budz, K. B. Buerkmann-Gehrlein, O. Dressler, H. A. Duerr, V. Duerr, W. Eberhardt, S. Eisebitt, J. Feikes, R. Follath, A. Gaupp, R. Goergen, K. Goldammer, S. C. Hessler, K. Holldack, E. Jaeschke, S. Klauke, J. Knobloch, O. Kugeler, B. C. Kuske, P. Kuske, A. Meseck, R. Mitzner, R. Mueller, M. Neeb, A. Neumann, K. Ott, D. Pfluckhahn, T. Quast, M. Scheer, Th. Schroeter, M. Schuster, F. Senf, G. Wuestefeld BESSY GmbH, Berlin D. Kramer GSI, Darmstadt F. Marhauser JLAB, Newport News, Virginia
	Funding: Bundesministerium fur Bildung und Forschung and the Land Berlin BESSY is proposing a demonstration facility, called STARS, for a two-stage high-gain harmonic generation free electron laser (HGHG FEL). STARS is planned for lasing in the wavelength range 40 to 70 nm, requiring a beam energy of 325 MeV. The facility consists of a normal conducting gun, three superconducting TESLA-type acceleration modules modified for CW operation, a single stage bunch compressor and finally a two-stage HGHG cascaded FEL. This paper describes the faciliy layout and the rationale behind the operation parameters.
TUPMN017	''Jitter Free'' FEL Pulses for Pump and Probe Experiments	953
	G. Wuestefeld R. Follath, A. Meseck BESSY GmbH, Berlin
	Funding: Bundesministerium fur Bildung und Forschung and the Land Berlin The cascaded High Gain Harmonic Generation (HGHG) scheme proposed for the BESSY-FEL contains an inherent potential for providing jitter free radiation pulses for pump and probe experiments. In an HGHG stage an energy modulation is imprinted to the electron beam by a seeding radiation. A dispersive section converts this energy modulation to a spatial modulation which is optimized for a particular harmonic. The subsequent radiator is optimized for this harmonics and generates radiation with high power which is used as seeding radiation for the next stage. After passage through the modulator, the seeding radiation become redundant and can be separated from the prebunched electrons using a deflecting dispersive chicane. This radiation and the final FEL output will have a fixed temporal separation as the first one is the driving seeding radiation for the second one. Using the planned test facility for HGHG scheme at BESSY as an example, we present simulation studies for a sequences of two jitter free pump and probe pulses including the deflecting chicane and a suitable beam line.
TUPMN018	Dark Current Transport in the FLASH Linac	956
	L. Froehlich
	The free electron laser facility FLASH at DESY Hamburg operates a low-emittance photoinjector and several acceleration modules with superconducting cavities to produce a high quality electron beam of up to 700 MeV. Since few months, the accelerator is routinely operated with its design RF pulse length of 800 μs instead of the prior length of 70-200 μs. As a result, the activation of components due to dark current emitted by the gun has reached critical proportions. To improve the understanding of dark current transport through the linac, simulations have been conducted with the Astra tracking code. The generated phase space distributions are compared against a detailed 3-dimensional aperture model of the machine with the newly developed ApertureLib toolkit. The results are in agreement with direct measurements of the dark current and with the observed activities.
TUPMN023	Status of the Optical Replica Synthesizer at FLASH	965
	S. Khan G. Angelova, V. G. Ziemann UU/ISV, Uppsala J. Boedewadt, A. Winter Uni HH, Hamburg M. Hamberg, N. X. Javahiraly, M. Larsson, P. Salen, P. van der Meulen FYSIKUM, AlbaNova, Stockholm University, Stockholm A. Meseck BESSY GmbH, Berlin E. Saldin, H. Schlarb, B. Schmidt, E. Schneidmiller, M. V. Yurkov DESY, Hamburg
	A novel laser-based method to measure the longitudinal profile of ultrashort electron bunches, known as Optical Replica Synthesizer, will be implemented at the free-electron laser FLASH at DESY. The paper describes its technical layout and the status of the project. E. Saldin, E. Schneidmiller, M. Yurkov, NIM A 539 (2005), 499
TUPMN028	The New Photoinjector for the Fermi Project	974
	G. D'Auria D. Bacescu, L. Badano, F. Cianciosi, P. Craievich, M. B. Danailov, G. Penco, L. Rumiz, M. Trovo, A. Turchet ELETTRA, Basovizza, Trieste H. Badakov, A. Fukasawa, B. D. O'Shea, J. B. Rosenzweig UCLA, Los Angeles, California
	FERMI@ELETTRA is a single-pass FEL user facility covering the spectral range 100 10 nm. It will be located near the Italian third generation Synchrotron Light Source facility ELETTRA and will make use of the existing 1.0 GeV normal conducting Linac. To obtain the high beam brightness required by the project, the present Linac electron source will be substituted with a photocathode RF gun now under development in the framework of a collaboration between Sincrotrone Trieste (ST) and Particle Beam Physics Laboratory (PBPL) at UCLA. The new gun will use an improved design of the 1.6 cell accelerating structure already developed at PBPL, scaled to 2998 MHz. We expect that the new gun design will allow a beam brightness increase by a factor 3-4 over the older version of the device. Some technical choices of the new design, including the enhancement of the mode separation, removal of the RF tuners, full cell symmetrization to limit the dipole and quadrupole RF field as well as an improved solenoid yoke design for multipole field corrections, will be discussed.
TUPMN029	Linac Upgrading Program for the Fermi Project : Status and Perspectives	977
	G. D'Auria D. Bacescu, L. Badano, C. Bontoiu, F. Cianciosi, P. Craievich, M. B. Danailov, S. Di Mitri, M. Ferianis, G. C. Pappas, G. Penco, A. Rohlev, A. Rubino, L. Rumiz, S. Spampinati, M. Trovo, A. Turchet, D. Wang ELETTRA, Basovizza, Trieste
	FERMI@ELETTRA is a soft X-ray forth generation light source under development at the ELETTRA laboratory. It will be based on the existing 1.0 GeV Linac, revised and upgraded to fulfil the stringent requirements expected from the machine. The overall time schedule of the project is very tight and ambitious, foreseeing to supply 10 nm photons to users within 2010. Here the machine upgrading program and the ongoing activities are presented and discussed.
TUPMN034	Comparison Between SPARC E-Meter Measurements and Simulations	986
	C. Ronsivalle A. Bacci, A. R. Rossi, L. Serafini INFN-Milano, Milano M. Boscolo, E. Chiadroni, M. Ferrario, D. Filippetto, V. Fusco, G. Gatti, M. Migliorati, A. Mostacci, C. Vaccarezza, C. Vicario INFN/LNF, Frascati (Roma) A. Cianchi INFN-Roma II, Roma L. Giannessi, M. Quattromini ENEA C. R. Frascati, Frascati (Roma) M. Petrarca Universita di Roma I La Sapienza, Roma
	For the SPARC photoinjector commissioning the emittance compensation process has been studied experimentally under different beam conditions (variation of charge, spot size, beam shape…) by a novel device called "emittance-meter", consisting in a movable emittance measurement system based on the 1D pepper pot method scanning a region 1.2 m long downstream the RF-gun. The results of a detailed comparison between the measurements and beam dynamics simulations performed by the different codes(PARMELA, HOMDYN, TREDI) employed for SPARC design are presented and discussed here.
TUPMN035	Generation of a Multipulse Comb Beam and a Relative Twin Pulse FEL	989
	M. Boscolo I. Boscolo, S. Cialdi, V. Petrillo INFN-Milano, Milano F. Castelli Universita degli Studi di Milano, Milano M. Ferrario, C. Vaccarezza INFN/LNF, Frascati (Roma)
	A radiofrequency electron gun joined to a compressor generates trains of THz subpicosecond electron pulses. Assuming a prompt electron emission, the laser train generates a train of electron disks at the cathode, then the disk train evolves towards a slug with a slight density modulation but also with a peculiar sawtooth energy modulation. This kind of energy modulation is transformed into a density modulation by a velocity bunching compressor recovering at a good extent the initial intensity beam profile. We study here through simulations the process looking to its characteristics as function peak and frequency characteristics of the laser and the parameters of the accelerator.
TUPMN036	Laser and RF Synchronization Measurements at SPARC	992
	A. Gallo M. Bellaveglia, G. Gatti, C. Vicario INFN/LNF, Frascati (Roma)
	Funding: Work supported by the EU Commission in the sixth framework programme, contract no. 011935 - EUROFEL. The SPARC project consists in a 150 MeV B-band, high-brilliance linac followed by 6 undulators for FEL radiation production at 530 nm. The linac assembly has been recently completed. During year 2006 a first experimental phase aimed at characterizing the beam emittance in the first 2m drift downstream the RF gun has been carried out. The low level RF control electronics to monitor and synchronize the RF phase in the gun and the laser shot on the photocathode has been commissioned and extensively tested during the emittance measurement campaign. The laser synchronization has been monitored by measuring the phase of the free oscillation of an RF cavity impulsively excited by the signal of a fast photodiode illuminated by the laser shot. Phase stability measurements are reported, both with and without feedback correction of the slow drifts. A fast intra-pulse phase feedback system to reduce the phase noise produced by the RF power station has been also positively tested.
TUPMN037	Power Tests of a PLD Film Mg Photo-cathode in a RF Gun	995
	G. Gatti L. Cultrera, F. Tazzioli INFN/LNF, Frascati (Roma) J. Moody, P. Musumeci UCLA, Los Angeles, California A. Perrone INFN-Lecce, Lecce
	Metallic film photo-cathodes are rugged, have a fast response and good emission uniformity. Mg has also a relevant Quantum Efficiency in the near UV. A cathode suitable for a 1.5 cells S-band RF gun has been produced by depositing an Mg film on Cu by Pulsed Laser Deposition technique. After different optimizations, stable good results have been reached in the low field measurement scenario. A sample was deposited on a gun flange and tested in the 1.6 cell injector at UCLA Pegasus facility to prove cathode resistence in a high field environment. The results are described.
TUPMN038	Coherent Cherenkov Radiation as a Temporal Diagnostic for Microbunched Beams	998
	G. Gatti A. M. Cook, J. B. Rosenzweig, R. Tikhoplav UCLA, Los Angeles, California
	Cherenkov radiation of a relativistic e-beam traversing a thin section of aerogel is analized, putting the stress on the coherent contribution due to the intra-beam, transverse and longitudinal structure. The use of this tool as a temporal diagnostic for micro-bunched beams makes possible to improve the amount of collected power at the microbunching frequency several orders of magnitude more respect to the uncoherent Cherenkov contribution. The non-idealities of a real beam are taken in account, and some techniques aimed on enhancing the coherent part of radiation are proposed and analized analitically and through simulation codes.
TUPMN039	Status of the SPARC-X Project	1001
	C. Vaccarezza D. Alesini, M. Bellaveglia, S. Bertolucci, R. Boni, M. Boscolo, M. Castellano, A. Clozza, L. Cultrera, G. Di Pirro, A. Drago, A. Esposito, M. Ferrario, L. Ficcadenti, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, A. Ghigo, C. Ligi, M. Migliorati, A. Mostacci, E. Pace, L. Palumbo, L. Pellegrino, M. A. Preger, R. Ricci, C. Sanelli, M. Serio, F. Sgamma, B. Spataro, A. Stella, F. Tazzioli, M. Vescovi, C. Vicario INFN/LNF, Frascati (Roma) F. Alessandria, A. Bacci, R. Bonifacio, I. Boscolo, F. Broggi, F. Castelli, S. Cialdi, C. De Martinis, A. F. Flacco, D. Giove, C. Maroli, V. Petrillo, A. R. Rossi, L. Serafini INFN-Milano, Milano M. Bougeard, P. Breger, B. Carre, D. Garzella, M. Labat, G. Lambert, H. Merdji, P. Monchicourt, P. Salieres, O. Tcherbakoff CEA, Gif-sur-Yvette L. Catani, E. Chiadroni, A. Cianchi, E. Gabrielli, C. Schaerf INFN-Roma II, Roma F. Ciocci, G. Dattoli, A. Dipace, A. Doria, F. Flora, G. P. Gallerano, L. Giannessi, E. Giovenale, G. Messina, P. L. Ottaviani, S. Pagnutti, G. Parisi, L. Picardi, M. Quattromini, A. Renieri, G. Ronci, C. Ronsivalle, M. Rosetti, E. Sabia, M. Sassi, A. Torre, A. Zucchini ENEA C. R. Frascati, Frascati (Roma) M.-E. Couprie SOLEIL, Gif-sur-Yvette P. Emma SLAC, Menlo Park, California M. Mattioli, D. Pelliccia Universita di Roma I La Sapienza, Roma P. Musumeci, M. Petrarca INFN-Roma, Roma C. Pellegrini, S. Reiche, J. B. Rosenzweig UCLA, Los Angeles, California A. Perrone INFN-Lecce, Lecce
	SPARC-X is a two branch project consisting in the SPARC test facility dedicated to the development and test of critical subsystems such as high brightness photoinjector and a modular expandable undulator for SASE-FEL experiments at 500 nm with seeding, and the SPARX facility aiming at generation of high brightness coherent radiation in the 3-13 nm range, based on the achieved expertise. The projects are supported by MIUR (Research Department of Italian Government) and Regione Lazio. SPARC has completed the commissioning phase of the photoinjector in November 2006. The achieved experimental results are here summarized together with the status of the second phase commissioning plans. The SPARX project is based on the generation of ultrahigh peak brightness electron beams at the energy of 1 and 2 GeV generating radiation in the 3-13 nm range. The construction is at the moment planned in two steps starting with a 1 GeV Linac. The project layout including both RF-compression and magnetic chicane techniques has been studied and compared, together with the feasibility of a mixed s-band and x-band linac option.
TUPMN041	Three Dimensional Analysis of the X-Radiation Produced by a Collective Thomson Source	1007
	V. Petrillo A. Bacci, C. Maroli, A. R. Rossi, L. Serafini, P. Tomassini INFN-Milano, Milano A. Colzato Universita degli Studi di Milano, Milano
	A set of 3-D equations that describes the collective head to head interaction between a laser pulse and a relativistic electron beam is presented and solved. The relevant dispersion relation is studied, as well as the gain properties of the system. The FEL instability dominates the radiation process. The radiation emitted is characterized by short wavelength, thin spectrum and high coherence. The most important three-dimensional effects are the emittance of the beam and the transverse distribution of the laser energy. The production of radiation wavelengths of 12 nm, 1nm, and 1 Angstron are presented.
TUPMN053	Status of the Photocathode RF Gun at Tsinghua University	1043
	Y.-C. Du W.-H. Huang, Y. Lin, C.-X. Tang, D. Xiang, L. X. Yan TUB, Beijing
	The photocathode RF gun at Tsinghua University was built to develop electron source for the Thomson Scattering X-ray source. The main goal is to produce minimum transverse emittance beams with short bunch length at medium charge (~1nC). It includes a 1.6 cell S-band BNL/KEK/SHI type cavity, a solenoid for space charge compensation, a laser system to generate UV light, and different diagnostics tools. In this paper, it will include measurements of the dark current, the charge and quantum efficiency, momentum, transverse electron beam profiles at different locations and the transverse emittance. This work was supported by the Chinese National Foundation of Natural Sciences under Contract no. 10645002.
TUPMN054	Design of a Source to Supply Ultra-fast Electron and X-Ray Pulses	1046
	W.-H. Huang H. Chen, Y.-C. Du, Hua, J. F. Hua, R. K. Li, Y. Lin, J. Shi, C.-X. Tang, D. Xiang, L. X. Yan, P.-CH. Yu TUB, Beijing
	In this paper we report the preliminary design and considerations on a multi-discipline ultra-fast source, which is capable of providing the user community with femtosecond electron bunch and light pulses with the wavelength ranging from IR to X-ray. The facility is based on photocathode RF gun driven by a Ti:Sapphire laser system. The low emittance subpicosecond electron bunch at the gun exit can be used in femtosecond electron diffraction setup to visualize the ultrafast structural dynamics. After acceleration and compression, the electron beam with the energy of 50 MeV is further used to provide high peak brightness X-ray by inverse Compton scattering with TW laser. We also consider the possibility and reliability of storing the electron beam in a compact storage ring and the laser pulse in a super-cavity. Operating in this scheme may increase the average flux of the X-ray photons by orders of magnitude.
TUPMN055	First Principle Measurements of Thermal Emittance for Copper and Magnesium	1049
	D. Xiang Y.-C. Du, W.-H. Huang, R. K. Li, Y. Lin, C.-X. Tang, L. X. Yan TUB, Beijing J. H. Park, S. J. Park PAL, Pohang, Kyungbuk
	Funding: This work was supported by the Chinese National Foundation of Natural Sciences under Contract no. 10645002. There are growing interests in generation, preservation and applications of high brightness electron beam. With the rapid development in the techniques for emittance compensation and laser shaping, we are approaching the limit-the uncorrelated thermal emittance. In this paper, we report the measurements of thermal emittance for Cu and Mg. The measurement is conducted in a field-free region. The energy spectrum and angular distribution of the electrons are measured immediately after its emission and further used to reconstruct the initial phase space and the corresponding thermal emittance. We also show how cathode surface roughness* and laser incidence angle as well as its polarization state** affect the quantum efficiency and thermal emittance. X. Z. He, High energy physics and nuclear physics,28(2004)1007.*Dao Xiang,et al, NIM A,562(2006)48.
TUPMN102	Electromagnetic Design of the RF Cavity Beam Position Monitor for the LCLS	1153
	G. J. Waldschmidt R. M. Lill, L. H. Morrison ANL, Argonne, Illinois
	Funding: Work supported by the U. S. Department of Energy under Contract Nos DE-AC02-06CH11357 and DE-AC03-76SF00515. A high-resolution X-band cavity beam position monitor (BPM) has been developed for the LCLS in order to achieve micron-level accuracy of the beam position using a dipole mode cavity and a monopole mode reference cavity. The rf properties of the BPM will be discussed in this paper including output power, tuning, and issues of manufacturing. In addition, methods will be presented for improving the isolation of the output ports to differentiate between horizontal/vertical beam motion and to reject extraneous modes from affecting the output signal. The predicted simulation results will be compared to data collected from low-power experimental tests.
TUPMN109	A High Repetition Rate VUV-Soft X-Ray FEL Concept	1167
	J. N. Corlett J. M. Byrd, W. M. Fawley, M. Gullans, D. Li, S. M. Lidia, H. A. Padmore, G. Penn, I. V. Pogorelov, J. Qiang, D. Robin, F. Sannibale, J. W. Staples, C. Steier, M. Venturini, S. P. Virostek, W. Wan, R. P. Wells, R. B. Wilcox, J. S. Wurtele, A. Zholents LBNL, Berkeley, California
	Funding: This work was supported by the Director, Office of Science, High Energy Physics, U. S. Department of Energy under Contract No. DE-AC02-05CH11231. The FEL process increases radiation flux by several orders of magnitude above existing incoherent sources, and offers the additional enhancements attainable by optical manipulations of the electron beam: control of the temporal duration and bandwidth of the coherent output, and wavelength; utilization of harmonics to attain shorter wavelengths; and precise synchronization of the x-ray pulse with laser systems. We describe an FEL facility concept based on a high repetition rate RF photocathode gun, that would allow simultaneous operation of multiple independent FELs, each producing high average brightness, tunable over the soft x-ray-VUV range, and each with individual performance characteristics determined by the configuration of the FEL SASE, enhanced-SASE (ESASE), seeded, self-seeded, harmonic generation, and other configurations making use of optical manipulations of the electron beam may be employed, providing a wide range of photon beam properties to meet varied user demands. FELs would be tailored to specific experimental needs, including production of ultrafast pulses even into the attosecond domain, and high temporal coherence (i.e. high resolving power) beams.
TUPMN113	A Plasma Channel Beam Conditioner for Free electron Lasers	1176
	G. Penn A. Sessler, J. S. Wurtele LBNL, Berkeley, California
	Funding: Work supported by the U. S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-05CH11231. By "conditioning" an electron beam, through establishing a correlation between transverse action and energy within the beam, the performance of free electron lasers (FELs) can be dramatically improved. Under certain conditions, the FEL can perform as if the transverse emittances of the beam were substantially lower than the actual values. After a brief review of the benefits of beam conditioning, we present a method to generate this correlation through the use of a plasma channel. The strong transverse focusing produced by a dense plasma (near standard gas density) allows the optimal correlation to be achieved in a reasonable length channel, of order 1 m. This appears to be a convenient and practical method for achieving conditioned beams, especially in comparison with other methods which require either a long beamline or multiple passes through some type of ring.
TUPMN114	Simulation of the Microbunching Instability in Beam Delivery Systems for Free Electron Lasers	1179
	I. V. Pogorelov J. Qiang, R. D. Ryne, M. Venturini, A. Zholents LBNL, Berkeley, California R. L. Warnock SLAC, Menlo Park, California
	In this paper, we examine the growth of the microbunching instability in the chain of linac sections and bunch compressor chicanes used in the electron beam delivery system of a free electron laser. We compare the results of two sets of simulations, one conducted using a direct Vlasov solver, the other using a particle-in-cell code Impact-Z with the number of simulation macroparticles ranging up to 100 million. The comparison is focused on the values of uncorrelated (slice) energy spread at different points in the lattice. In particular, we discuss the interplay between physical and numerical noise in particle-based simulations, and assess the agreement between the simulation results and theoretical predictions.
TUPMN119	Energy Recovery Transport Design for Peking University FEL	1191
	G. M. Wang Y.-C. Chao Jefferson Lab, Newport News, Virginia J.-E. Chen, C. Liu, Z. C. Liu, X. Y. Lu, K. Zhao, J. Zhuang PKU/IHIP, Beijing
	Funding: supported by National 973 Projects and the U. S. Department of Energy Contract No. DE-AC05-06OR23177 A free-electron laser based on a superconducting linac is under construction in Peking University. To increase FEL output power, energy recovery is chosen as one of the most potential and popular ways. The design of a beam transport system for energy recovery is presented, which is suitable for the Peking University construction area. Especially, a chicane structure is chosen to change path length at ±20 degree and M56 in the arc is adjusted for fully bunch compression.
TUPMS005	Quiet Start Method in HGHG Simulation	1200
	Y. Hao L.-H. Yu BNL, Upton, Long Island, New York
	Funding: Work supported by U. S. DOE under contract No DE-FG02-92ER40747 and U. S NSF under contract No PHY-0552389 Quiet start scheme is broadly utilized in Self Amplified Spontaneous Radiation (SASE) FEL simulations, which is proven to be correct and efficient. Nevertheless, due to the existing of energy modulation effect and the dispersion section, the High Gain Harmonic Generation (HGHG) FEL simulation will not be improved by the traditional quiet start method. A new approach is presented to largely decrease the macro-particles per slice that can be implemented in both time-independent and time-dependent simulation, accordingly expedites the HGHG FEL simulation especially high order harmonic cascade case and makes the multi-parameter scanning be possible.
TUPMS034	Seeded VISA: A 1064 nm Laser-Seeded FEL Amplifier at the BNL ATF	1257
	M. P. Dunning G. Andonian, E. Hemsing, S. Reiche, J. B. Rosenzweig UCLA, Los Angeles, California M. Babzien, V. Yakimenko BNL, Upton, Long Island, New York
	An experimental study of a seeded free electron laser (FEL) using the VISA undulator and a Nd:YAG seed laser will be performed at the Accelerator Test Facility at Brookhaven National Laboratory. The study is motivated by the demand for a short Rayleigh length FEL amplifier at 1 micron for high power transmission with minimal damage of transport optics. Planned measurements include transverse and longitudinal coherence, angular distribution, and wavelength spectrum of the FEL radiation. The effects of detuning the electron beam energy will be studied, with an emphasis on control of the radiation emission angles and increase of the amplifier efficiency. Results of start-to-end simulations will be presented with preliminary experimental results.
TUPMS036	Characterization of Orbital Angular Momentum Modes in FEL Radiation	1263
	E. Hemsing G. Andonian, J. B. Rosenzweig UCLA, Los Angeles, California M. Babzien, V. Yakimenko BNL, Upton, Long Island, New York A. Gover University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
	Optical guiding of the radiation pulse through the source electron bunch in a free-electron laser is a well known phenomena that suppresses diffraction of the output radiation, and thus enhances the gain. The resulting radiation can be described by an expansion of orthogonal modes that are also composed of eigenstates of orbital angular momentum (OAM). In the VISA-FEL experiment at the ATF-BNL, gain guiding has been observed under self-amplified spontaneous emission conditions at 840 nm with a strongly chirped input electron beam. The resulting far-field transverse radiation profiles are observed to contain multiple modes in the angular intensity spectrum, and exhibit both hollow and spiral structures characteristic of single or multiply interfering OAM modes. Current efforts to characterize the transverse radiation profile both experimentally and through start-to-end simulations are presented.
TUPMS037	Simulation of an Iris-guided Inverse Free-electron Laser Micro-bunching Experiment	1266
	J. T. Frederico G. Gatti INFN/LNF, Frascati (Roma) S. Reiche, R. Tikhoplav UCLA, Los Angeles, California
	The Free-Electron Laser code Genesis 1.3 has been modified to include waveguides within the undulator, reducing the diffraction effects for long wavelength FELs. Several types of waveguides are considered, which are rectangular and circular waveguides as well as iris-loaded open waveguides. Studies are presented here on the enhancement of FEL and IFEL with these wave-guiding structures in comparison to free-space propagation of the radiation wave.
TUPMS038	Recent Upgrade to the Free-electron Laser Code Genesis 1.3	1269
	S. Reiche K. Goldammer BESSY GmbH, Berlin P. Musumeci Rome University La Sapienza, Roma
	The time-dependent code GENESIS 1.3 has be modified to address new problems in modeling Free-electron Lasers. The functionality has been extended to include higher harmonics and to allow for a smoother modeling of cascading FELs. The code has been also exported to a parallel computer architecture for faster execution using the MPI protocol.
TUPMS039	Coherence Properties of the LCLS X-ray Beam	1272
	S. Reiche
	Self-amplifying spontaneous radiation free-electron lasers, such as the LCLS or the European X-FEL, rely on the incoherent, spontaneous radiation as the seed for the amplifying process. Though this method overcomes the need for an external seed source one drawback is the incoherence of the effective seed signal. The FEL process allows for a natural growth of the coherence because the radiation phase information is spread out within the bunch due to slippage and diffraction of the radiation field. However, at short wavelengths this spreading is not sufficient to achieve complete coherence. In this presentation we report on the results of numerical simulations of the LCLS X-ray FEL. From the obtained radiation field distribution the coherence properties are extracted to help to characterize the FEL as a light source.
TUPMS041	The Wisconsin VUV/Soft X-ray Free Electron Laser Project	1278
	J. Bisognano R. A. Bosch, M. A. Green, H. Hoechst, K. Jacobs, K. J. Kleman, R. A. Legg, R. Reininger, R. Wehlitz UW-Madison/SRC, Madison, Wisconsin J. Chen, W. Graves, F. X. Kaertner, J. Kim, D. E. Moncton MIT, Cambridge, Massachusetts
	Funding: Work supported by the University of Wisconsin - Madison. SRC is supported by the U. S. National Science Foundation under Award No. DMR-0537588. The University of Wisconsin-Madison and its partners are developing a design for an FEL operating in the UV to soft x-ray range that will be proposed as a new multidisciplinary user facility. Key features of this facility include seeded, fully coherent output with tunable photon energy and polarization over the range 5 eV to 1240 eV, and simultaneous, independent operation of multiple beamlines. The different beamlines will support a wide range of science from femto-chemistry requiring ultrashort pulses with kHz repetition rates to photoemission and spectroscopy requiring high average flux and narrow bandwidth at MHz rates. The facility will take advantage of the flexibility, stability, and high average pulse rates available from a CW superconducting linac driven by a photoinjector. This unique facility is expected to enable new science through ultra-high resolution in the time and frequency domains, as well as coherent imaging and nano-fabrication. This project is being developed through collaboration between the UW Synchrotron Radiation Center and MIT. We present an overview of the facility, including the motivating science, and its laser, accelerator, and experimental systems.
TUPMS042	A Superconducting Linac Driver for the Wisconsin Free Electron Laser	1281
	J. Bisognano R. A. Bosch, M. A. Green, K. Jacobs, K. J. Kleman, R. A. Legg UW-Madison/SRC, Madison, Wisconsin J. Chen, W. Graves, F. X. Kaertner, J. Kim MIT, Cambridge, Massachusetts
	Funding: Work supported by the University of Wisconsin - Madison. SRC is supported by the U. S. National Science Foundation under Award No. DMR-0537588. We present an initial design of the driver for the Wisconsin VUV/Soft Xray FEL facility, which will provide high intensity coherent photons from 5 eV to 1.2 keV. It uses a 2.5 GeV, L-band CW superconducting linac with a 1.7 GeV tap-off to feed the lower energy FELs. In order to support multiple high rep-rate FELs, the average design current is 1 mA. Sub-nanocoulomb bunches with normalized transverse emittances of order 1 micron are generated in a photoinjector for beamlines operating at repetition rates from kHz to MHz. Multi-stage bunch compression provides 1 kA peak current to the FELs, with low energy spread and a suitable current profile. Compressed bunch lengths of several hundred femtoseconds will allow generation of photon pulses in the range 10 to 100 fs using cascaded FELs. Consideration has been given to removing the residual energy chirp from the beam, and minimizing the effects of space charge, coherent synchrotron radiation, and microbunching instabilities. A beam switchyard using RF separators and fast kickers delivers the desired electron bunches to each of the FELs. Details of the design will be presented, including those areas requiring the most development work.
TUPMS046	Integration of the Optical Replica Ultrashort Electron Bunch Diagnostics with the Current-Enhanced SASE in the LCLS	1293
	Y. T. Ding P. Emma, Z. Huang SLAC, Menlo Park, California
	In this paper, we present a feasibility study of integrating the optical replica (OR) ultrashort electron bunch diagnostics * with the current-enhanced SASE (ESASE) scheme ** in the LCLS. Both techniques involve using an external laser to energy-modulate the electron beam in a short wiggler and converting the energy modulation to a density modulation in a dispersive section. While ESASE proposes to use the high-current spikes to enhance the FEL signal, the OR method extracts the optical coherent radiation produced by a density modulated electron beam for frequency resolved optical gating (FROG) diagnostics. We discuss the optimization studies of combining the OR method with the ESASE after the second bunch compressor in the LCLS. Simulation results show that the OR method is capable of reproducing the expected double-horn current profile of a 200-fs bunch. The possibilities and limitations of reconstructing the longitudinal phase space profile are also explored. * E. Saldin et al, Nucl. Instr. and Meth. A 539, 499 (2005).** A. Zholents, Phys. Rev. ST Accel. Beams 8, 040701 (2005); A. Zholents et al., in Proceedings of FEL2004, 582 (2004).
TUPMS047	Results of the SLAC LCLS Gun High-Power RF Tests	1296
	D. Dowell E. N. Jongewaard, J. R. Lewandowski, Z. Li, C. Limborg-Deprey, J. F. Schmerge, A. E. Vlieks, J. W. Wang, L. Xiao SLAC, Menlo Park, California
	Funding: SLAC is operated by Stanford University for the Department of Energy under contract number DE-AC03-76SF00515. The beam quality and operational requirements for the Linac Coherent Light Source (LCLS) currently being constructed at SLAC are exceptional, requiring the design of a new RF photocathode gun for the electron source. Based on operational experience at GTF at SLAC, SDL and ATF at BNL and other laboratories, the 1.6cell s-band (2856MHz) gun was chosen to be the best electron source for the LCLS injector, however a significant re-design was necessary to achieve the challenging parameters. Detailed 3-D analysis and design was used to produce nearly-perfect rotationally symmetric rf fields to achieve the emittance requirement. In addition, the thermo-mechanical design allows the gun to operate at 120Hz and a 140MV/m cathode field, or to an average power dissipation of 4kW. Both average and pulsed heating issues are addressed in the LCLS gun design. The first LCLS gun is now fabricated and has been operated with high-power RF. The results and analysis of these high-power tests will be presented.
TUPMS048	Measurement and Analysis of Field Emission Electrons in the LCLS Gun	1299
	D. Dowell E. N. Jongewaard, C. Limborg-Deprey, J. F. Schmerge, A. E. Vlieks SLAC, Menlo Park, California
	Funding: SLAC is operated by Stanford University for the Department of Energy under contract number DE-AC03-76SF00515. The field emission was measured during the high-power testing of the LCLS photocathode RF gun. A careful study and analysis of the field emission electrons, or dark current is important in assessing the gun's internal surface quality in actual operation, especially those surfaces with high fields. The charge per 2 microsecond long RF pulse (the dark charge) was measured as a function of the peak cathode field for the 1.6 cell, 2.856GHz LCLS RF gun. Faraday cup data was taken for cathode peak RF fields up to 120MV/m producing a maximum of 0.6nC/RF pulse for a diamond-turned polycrystalline copper cathode installed in the gun. The field dependence of the dark charge is analyzed using a temperature-dependent Fowler-Nordheim (FN) theory to obtain the field enhancement factor and other emitter parameters. Digitized images of the dark charge were taken using a 100 micron thick YAG crystal for a range of solenoid fields to determine the location and angular distribution of the field emitters. The FN plots and emitter image analysis will be described in this paper.
TUPMS049	Initial Commissioning Experience with the LCLS Injector	1302
	P. Emma R. Akre, J. Castro, Y. T. Ding, D. Dowell, J. C. Frisch, A. Gilevich, G. R. Hays, P. Hering, Z. Huang, R. H. Iverson, P. Krejcik, C. Limborg-Deprey, H. Loos, A. Miahnahri, C. H. Rivetta, M. E. Saleski, J. F. Schmerge, D. C. Schultz, J. L. Turner, J. J. Welch, W. E. White, J. Wu SLAC, Menlo Park, California L. Froehlich, T. Limberg, E. Prat DESY, Hamburg
	Funding: U. S. Department of Energy contract #DE-AC02-76SF00515. The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) project presently under construction at SLAC. The injector section, from drive-laser and RF photocathode gun through the first bunch compressor chicane, was installed during the Fall of 2006. Initial system commissioning with an electron beam takes place in the Spring and Summer of 2007. The second phase of construction, including the second bunch compressor and the FEL undulator, will begin later, in the Fall of 2007. We report here on experience gained during the first phase of machine commissioning, including RF photocathode gun, linac booster section, energy spectrometers, S-band and X-band RF systems, the first bunch compressor stage, and the various beam diagnostics.
TUPMS062	National High Magnetic Field Laboratory FEL Injector Design Consideration	1323
	P. Evtushenko S. V. Benson, D. Douglas, G. Neil Jefferson Lab, Newport News, Virginia
	A Numerical study of beam dynamics was performed for two injector systems for the proposed National High Magnetic Field Laboratory at the Florida State University (FSU) Free Electron Laser (FEL) facility. The first considered a system consisting of a thermionic DC gun, two buncher cavities operated at 260 MHz and 1.3 GHz and two TESLA type cavities, and is very similar to the injector of the ELBE Radiation Source. The second system we studied uses a DC photogun (a copy of JLab FEL electron gun), one buncher cavity operated at 1.3 GHz and two TESLA type cavities. The study is based on PARMELA simulations and takes into account operational experience of both the JLab FEL and the Radiation Source ELBE. The simulations predict the second system will have a much smaller longitudinal emittance. For this reason the DC photo gun based injector is preferred for the proposed FSU FEL facility.
TUPMS065	JLAMP: An Amplifier Based FEL in the JLab SRF ERL Driver	1329
	K. Jordan S. V. Benson, D. Douglas, P. Evtushenko, C. Hernandez-Garcia, G. Neil Jefferson Lab, Newport News, Virginia
	Funding: This work supported by the Off. of Naval Research, the Joint Technology Off., the Commonwealth of Virginia, the Air Force Research Lab, Army Night Vision Lab, and by DOE Contract DE-AC05-060R23177. Notional designs for ERL-driven high average power free electron lasers often invoke amplifier-based architectures. To date, however, amplifier FELs have been limited in average power output to values several orders of magnitude lower than those demonstrated in optical-resonator based systems; this is due at least in part to the limited electron beam powers available from their driver accelerators. In order to directly contrast the performance available from amplifiers to that provided by high-power cavity-based resonators, we have developed a scheme to test an amplifier FEL in the JLab SRF ERL driver. We describe an accelerator system design that can seamlessly and non-invasively integrate a 10 m wiggler into the existing system and which provides, at least in principle, performance that would support high-efficiency lasing in an amplifier configuration. Details of the design and an accelerator performance analysis will be presented.
TUPMS088	Efficiency Enhancement Experiment with a Tapered Undulator in a Single-pass Seeded FEL at the NSLS SDL	1371
	T. Watanabe D. A. Harder, R. K. Li, J. B. Murphy, G. Rakowsky, Y. Shen, X. J. Wang BNL, Upton, Long Island, New York
	Funding: This work is supported by the Office of Naval Research under contract No. N0002405MP70325 and U. S. Department of Energy under contract No. DE-AC02-98CH1-886. We report the experimental characterization of the FEL efficiency enhancement using a tapered undulator in a single-pass seeded FEL amplifier at the NSLS SDL. The last 3 m of the 10 m NISUS undulator was linearly tapered so that the magnetic field strength at the end of the undulator was reduced by 5 %. The FEL energy gain along the undulator was measured for both the tapered and un-tapered undulator. The FEL energy with the taper was measured to be about 3.2 times higher than that without the taper. We also experimentally characterized the spectrum and the transverse distribution of the FEL light for both the tapered and un-tapered undulator. The experimental results are compared with the numerical simulation code, GENESIS 1.3.
TUPMS091	A Theoretical Photocathode Emittance Model Including Temperature and Field Effects	1377
	K. Jensen D. W. Feldman, P. G. O'Shea UMD, College Park, Maryland N. A. Moody LANL, Los Alamos, New Mexico J. J. Petillo SAIC, Burlington, Massachusetts
	Funding: We gratefully acknowledge funding by the Joint Technology Office and the Office of Naval Research. A recently developed model* of the emittance and brightness of a photocathode based on the evaluation of the moments of the electron emission distribution function admits an analytical solution for the zero-field and zero-temperature asymptotic model. Here, the model has been extended to account for the critical modifications of temperature and field dependence, which are tied to material issues with the cathode. Temperature impacts the nature of scattering within the photoemitter material and therefore affects quantum efficiency significantly. Field changes the emission probability at the surface barrier, and is particularly important for low work function coatings, as occur for the cesiated surfaces characteristic of our controlled porosity dispenser photocathodes. Extensions of the theoretical models shall be given, followed by an analysis of their comparison with numerical simulations of the intrinsic emittance and brightness of a photocathode. The methodology is designed to facilitate the development of photoemission models into comprehensive particle-in-cell (PIC) codes to address issues otherwise not readily treated, e.g., variation in surface coverage and topology. * K. L. Jensen, P. G. O'Shea, D. W. Feldman, and N. A. Moody, Applied Physics Letters 89, 224103 (2006).