• A. Zholents
  

Subpicosecond x-ray pulses are now routinely obtained at the ALS, BESSY and SLS light sources using laser e-beam slicing technique. Other x-ray pulse shortening techniques were also proposed and are now under consideration for ALS, APS, DIAMOND and PETRA light sources. In this talk I review current results and discuss R&D plans and activity.

• 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

• S. V. Benson
  
• K. Beard, G. H. Biallas, J. Boyce, D. B. Bullard, J. L. Coleman, D. Douglas, H. F.D. Dylla, R. Evans, P. Evtushenko, C. W. Gould, A. C. Grippo, J. G. Gubeli, D. Hardy, C. Hernandez-Garcia, C. Hovater, K. Jordan, J. M. Klopf, R. Li, S. W. Moore, G. Neil, M. Poelker, T. Powers, J. P. Preble, R. A. Rimmer, D. W. Sexton, M. D. Shinn, C. Tennant, R. L. Walker, G. P. Williams, S. Zhang
  Jefferson Lab, Newport News, Virginia

Operation of the JLab IR Upgrade FEL at CW powers in excess of 10 kW requires sustained production of high electron beam powers by the driver ERL. This in turn demands attention to numerous issues and effects, including: cathode lifetime; control of beamline and RF system vacuum during high current operation; longitudinal space charge; longitudinal and transverse matching of irregular/large volume phase space distributions; halo management; management of remnant dispersive effects; resistive wall, wake-field, and RF heating of beam vacuum chambers; the beam break up instability; the impact of coherent synchrotron radiation (both on beam quality and the performance of laser optics); magnetic component stability and reproducibility; and RF stability and reproducibility. We discuss our experience with these issues and describe the modus vivendi that has evolved during prolonged high current, high power beam and laser operation.

• H. L. Andrews
  
• C. H. Boulware, C. A. Brau, J. D. Jarvis
  Vanderbilt University, Nashville, Tennessee

• H. Toyokawa
  
• H. Ikeura-Sekiguchi, M. K. Koike, R. Kuroda, H. Ogawa, N. Sei, M. Tanaka, K. Y. Yamada, M. Y. Yasumoto
  AIST, Tsukuba, Ibaraki
• T. Nakajyo, F. Sakai, T. Y. Yanagida
  SHI, Tokyo

• G. Neil
  

• K. C.D. Chan
  
• A. J. Jason, P. J. Turchi
  LANL, Los Alamos, New Mexico

For national security, it is important to detect the presence of Special Nuclear Materials (SNM), especially Highly-Enriched Uranium (HEU). Generally used methods for such detection include interrogation by photons and neutrons. For example, photofission in HEU can be initiated with 14-MeV photons. The resulting delayed neutrons and photons from the fission fragments are clear signatures of the presence of HEU. One can generate high-energy photons using electron accelerators via various mechanisms. In this paper, we will describe two of them, namely electron bremsstrahlung and Compton-backscattered photons. We focus on these two mechanisms because they cover a wide range of accelerator requirements. Electron bremsstrahlung can be generated using a compact low-energy electron linac while the generation of Compton-backscattered photons requires a high-energy electron accelerator of a few hundred MeV. We review these two options, describe their accelerator requirements, and compare their relative merits.

• F. Ludwig
  
• B. Lorbeer, H. Schlarb, A. Winter
  DESY, Hamburg

The next generation of FEL's (Free Electron Lasers) require a long and short term stable synchronisation of RF reference signals with an accuracy of 10 fs. For that an optical synchronisation system is developed for FLASH at DESY, that is based on optical pulse train which carry the timing information encoded in its precise repetition rate. The optical pulse train has to be converted into an RF signal to provide a local reference for calibration and operation of RF based devices. The drift and jitter performance of the optical to RF converter influences directly the phase stability of the accelerator. Three different methods for optical to RF converters, namely the direct photodiode detection, injection locking and a sagnac loop interferometer are currently under investigation. In this paper we concentrate on the jitter and drift performance of the direct photodiode conversion and show its limitations from measurement results.

• A. Winter
  
• W. J. Jalmuzna
  Warsaw University of Technology, Institute of Electronic Systems, Warsaw
• F. Loehl, H. Schlarb, P. Schmuser
  DESY, Hamburg

• I. Sugai
  
• T. Hattori, K. K. Kawasaki
  Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Tokyo
• Y. Irie
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• H. Kawakami, M. Oyaizu, A. Takagi, Y. Takeda
  KEK, Ibaraki

• D. P. Missiaen
  
• P. Bestmann, M. C.L. Buzio, S. D. Fartoukh, M. Giovannozzi, J. B. Jeanneret, A. M. Lombardi, Y. Papaphilippou, S. Pauletta, J. C. Perez, H. Prin, E. Y. Wildner
  CERN, Geneva

• E. Y. Wildner
  
• N. Emelianenko
  CERN, Geneva

• L. Tsai
  
• T.-C. Fan, C.-S. Hwang, C. J. Lin, S. Y. Perng, D.-J. Wang
  NSRRC, Hsinchu

• A. Bosco
  
• G. A. Blair, S. T. Boogert, G. E. Boorman
  Royal Holloway, University of London, Surrey

Electro-optic techniques might allow implementing a laserwire scanner for intra-train scanning at the ILC with scanning speed in excess of 100 kHz. A scanner capable of running at such a rate would in fact provide information about the particle beam size in about one hundred different positions along the bunch train (approximately 1ms long for the ILC*). The design of an electro-optic deflector capable to scan within 10-100 microsecond is presented, discussed and analytically treated.

* ILC Baseline Conceptual Design (2006).: http://www.linearcollider.org/.

• J. Ruan
  
• H. Edwards, R. P. Fliller, J. K. Santucci
  Fermilab, Batavia, Illinois

The current Fermilab A0 Photoinjector laser system includes a seed laser, a flashlamp pumped multipass amplifier cavity, a flashlamp pumped 2-pass amplifier system followed by an IR to UV conversion stage. However the current system can only deliver up to 800 pulses due to the low efficiency of Nd:Glass used inside multi-pass cavity. In this paper we will report the effort to develop a new multi pass cavity based on Nd:YLF crystal end-pumped by diode laser. We will also discuss the foreseen design of the laser system for the NML accelerator test facility at Fermilab.

• J. W. Staples
  
• J. M. Byrd, R. B. Wilcox
  LBNL, Berkeley, California

Long-term phase drifts of less than a femtosecond per hour have been demonstrated in a 2 km length of single-mode optical fiber, stabilized interferometrically at 1530 nm. Recent improvements include a wide-band phase detector that reduces the possibility of fringe jumping due to fast external perturbations of the fiber and locking of the master CW laser wavelength to a molecular absorption line. Mode-locked lasers may be synchronized using two wavelengths of the comb, multiplexed over one fiber, each wavelength individually interferometrically stabilized.

• D. G. Ouzounov
  
• I. V. Bazarov, B. M. Dunham, C. K. Sinclair
  Cornell University, Department of Physics, Ithaca, New York
• F. W. Wise, S. Zhou
  Cornell University, Ithaca, New York

Cornell University is developing a high brightness, high average current electron source for the injector of an ERL based synchrotron radiation source. The source is a DC electron gun with a negative electron affinity photoemission cathode. The photocathode is illuminated by a 1300 MHz CW train of optical pulses to produce a 100 mA average current beam. The optical pulse train is generated by frequency doubling the output of a diode-pumped, mode-locked Yb-fiber oscillator-amplifier system. The 50 MHz fundamental frequency oscillator is locked on its 26th harmonic to produce the 1300 MHz train. The oscillator output is amplified in three stages and doubled to give 26 W in the green. The doubled beam is diffraction limited (M2 = 1.08) with a pulse width of 2.5 ps. This pulse is split and differentially delayed in a series of birefringent crystals to produce a flat top temporal profile with fast rise and fall times. The final pulse shape is measured by cross-correlation. The pulses are spatially shaped by a commercial aspheric lens system. A full power system operating at 50 MHz is in routine use for electron beam measurements. Detailed laser performance information will be presented.

• M. Shverdin
  
• S. G. Anderson, C. P.J. Barty, M. Betts, D. J. Gibson, F. V. Hartemann, J. Hernandez, M. Johnson, I. Jovanovic, D. P. McNabb, M. J. Messerly, J. A. Pruet, C. Siders, A. M. Tremaine
  LLNL, Livermore, California

The fiber-based, spatially and temporally shaped, picosecond UV laser system described here has been specifically designed for advanced rf gun applications, with a special emphasis on the production of high-brightness electron beams for free-electron lasers and Compton scattering light sources. The laser pulse can be shaped to a flat-top in both space and time with a duration of 10 ps FWHM and rise and fall times under 1 ps. The pulse energy is 100 micro-joules at 261.75 nm and the spot size diameter of the beam at the photocathode measures 2 mm. A fiber oscillator and amplifier system generates a chirped pump pulse at 1047 nm; stretching is achieved in a chirped fiber Bragg grating. A single multi-layer dielectric grating based compressor recompresses the input pulse to 250 fs FWHM and a two stage harmonic converter frequency quadruples the beam. A custom-designed diffractive optic reshapes the input pulse to a flat-top. Temporal shaping is achieved with a Michelson-based ultrafast pulse stacking device with nearly 100% throughput. The integration of the system, as well as preliminary electron beam measurements will be discussed.

• J. Musson
  
• J. M. Grames, J. Hansknecht, R. Kazimi, M. Poelker
  Jefferson Lab, Newport News, Virginia

Recent upgrades to the CEBAF Polarized Source include a fiber-based seed laser, capable of producing pulses with frequency centered at 499 MHz. Combined with the existing three-beam Chopper, an aliasing, or beat frequency technique is used to produce long time intervals between individual electron microbunches (tens of nanoseconds) by merely varying the nominal 499 MHz drive laser frequency by <20%. This RF Laser modulator uses a divider and heterodyne scheme to maintain coherence with the accelerator Master Oscillator, while providing delay resolution in increments of 2ns. Laser repetition frequencies producing bunch repetition rates between 20 MHz and 100 MHz are demonstrated, resulting in time delays between 50 and 10 ns, respectively. Also, possible uses for such a beam are discussed as well as intended development. Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177

• P. He
  
• M. Anerella, S. Aydin, G. Ganetis, M. Harrison, A. K. Jain, B. Parker
  BNL, Upton, Long Island, New York

The conceptual design of compact superconducting magnets for the International Linear Collider final focus is presently under development at BNL. A primary concern in using superconducting quadrupoles is the potential for inducing additional vibrations from cryogenic operation. We have employed a Laser Doppler Vibrometer system to measure the vibrations at resolutions ~1 nm (at frequencies above ~8 Hz) in a spare RHIC quadrupole coldmass under cryogenic conditions. Some preliminary results of these studies were presented at the Nanobeam 2005 workshop*. These results were limited in resolution due to a rather large motion of the laser head itself. As a first step towards improving the measurement quality, an actively stabilized isolation table was used to reduce the motion of the laser holder. The improved set-up will be described, and vibration spectra measured at cryogenic temperatures, both with and without helium flow, will be presented.

*A. Jain, et al., Nanobeam 2005, Kyoto, Japan, Oct.17-21, 2005; paper WG2d-05; available at http://wwwal.kuicr.kyoto-u.ac.jp/NanoBM .

• P. I. Pavlishin
  
• M. Babzien, I. Pogorelsky, D. Stolyarov, V. Yakimenko
  BNL, Upton, Long Island, New York
• M. S. Zolotorev
  LBNL, Berkeley, California

Optical stochastic cooling for the Relativistic Heavy Ion Collider (RHIC) based on optical parametric amplification was proposed by M. Babzien et al., Phys. Rev. ST Accel. Beams v.7, 012801, (2004). According to this proposal a CdGeAs2 nonlinear crystal is used as an active medium for the optical parametric amplifier because of extremely large nonlinear coefficient, wide transparency range, and possibility to be phase matched over the required spectral range. We discuss experimental results of the parametric amplifier gain and coherency for the conditions applicable to optical stochastic cooling for RHIC.

• P. Chen
  
• M. Lundquist, R. Yi, D. Yu
  DULY Research Inc., Rancho Palos Verdes, California

High-gradient electron guns can suppress space-charge induced transverse emittance growth when the electron beam is still in the low-energy injection stage. A synchronizable, high-voltage pulser can be used to power up a high-gradient gun. We propose to build a 200 kV pulser using a special trigger that utilizes a laser-photocathode sub-system. A laser trigger beam will first energize a spark gap, and then provide a second trigger signal from a photocathode using its leftover energy, to further close the gap. This system will not only raise the utilization efficiency of the laser beam energy, but also enhance the reliability of the trigger circuit. Our preliminary analysis shows that the proposed system will significantly improve the performance of the laser trigger pulse with the jitter on the order of hundreds of picoseconds. It is expected that the pulser can be used in the applications of high gradient guns as well as in other devices that need high precision trigger such as short pulse lasers, streak cameras, impulse radiating antennas, etc.

• J. J. Petillo
  
• K. Jensen, B. Levush
  NRL, Washington, DC
• J. N. P. Panagos
  SAIC, Burlington, Massachusetts

Low emittance, high current density sources are required to achieve the small beam size needed for high frequency vacuum electronic devices and for high power free electron lasers (FELs). Emission models are of particular importance in the emittance-dominated regime, where emission non-uniformity and surface structure of the cathode can have an impact on beam characteristics. We have been developing comprehensive time-dependent photoemission models for the simulation codes that account for laser and cathode material and surface characteristics. MICHELLE* is NRL's finite-element self-consistent electrostatic time-domain code: it has the ability to import an RF field, and has unique capabilities for modeling the emission and the self fields, near the cathode. In particular, some instances of surface irregularities and emission non-uniformity (due to work function variation) leading to such effects as beam emittance and high frequency oscillations are possible to model due to the code's conformal meshing capabilities. We will present results of the implementation of the 'next generation' photoemission models in the MICHELLE code for modeling surface roughness and non-uniformity.

* John Petillo, et al., "The MICHELLE Three-Dimensional Electron and Collector Modeling Tool: Theory and Design", IEEE Trans. Plasma Sci., vol. 30, no. 3, June 2002, pp. 1238-1264.

• 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

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.

• T. Quast
  
• A. Firsov, K. Holldack
  BESSY GmbH, Berlin
• S. Khan
  Uni HH, Hamburg
• R. Mitzner
  Universität Muenster, Physikalisches Institut, Muenster

• G. Wuestefeld
  
• R. Follath, A. Meseck
  BESSY GmbH, 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.

• T. Limberg
  
• B. Beutner, W. Decking, M. Dohlus, K. Floettmann, M. Krasilnikov
  DESY, Hamburg

• J. S. Sekutowicz
  
• M. Ferrario
  INFN/LNF, Frascati (Roma)
• J. Iversen, D. Klinke, D. Kostin, W.-D. Moller, A. Muhs
  DESY, Hamburg
• P. Kneisel
  Jefferson Lab, Newport News, Virginia
• K. Ko, Z. Li, L. Xiao
  SLAC, Menlo Park, California
• R. S. Lefferts, A. R. Lipski
  SBUNSL, Stony Brook, New York
• T. Rao, J. Smedley
  BNL, Upton, Long Island, New York
• P. Strzyzewski
  The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock

• 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

* E. Saldin, E. Schneidmiller, M. Yurkov, NIM A 539 (2005), 499

• 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

• A. Gallo
  
• M. Bellaveglia, G. Gatti, C. Vicario
  INFN/LNF, Frascati (Roma)

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.

• G. Gatti
  
• L. Cultrera, F. Tazzioli
  INFN/LNF, Frascati (Roma)
• J. Moody, P. Musumeci
  UCLA, Los Angeles, California
• A. Perrone
  INFN-Lecce, Lecce

• C. Vicario
  
• M. Bellaveglia, D. Filippetto, A. Gallo, G. Gatti, A. Ghigo
  INFN/LNF, Frascati (Roma)
• S. Cialdi
  INFN-Milano, Milano
• P. Musumeci, M. Petrarca
  INFN-Roma, Roma

• V. Petrillo
  
• A. Bacci, C. Maroli, A. R. Rossi, L. Serafini, P. Tomassini
  INFN-Milano, Milano
• A. Colzato
  Universita degli Studi di Milano, Milano

• T. Kasuga
  
• T. A. Agoh, A. Enomoto, S. Fukuda, K. Furukawa, T. Furuya, K. Haga, K. Harada, S. Hiramatsu, T. Honda, K. Hosoyama, M. Izawa, E. Kako, H. Kawata, M. Kikuchi, Y. Kobayashi, M. Kuriki, T. Mitsuhashi, T. Miyajima, S. Nagahashi, T. Naito, T. Nogami, S. Noguchi, T. Obina, S. Ohsawa, M. Ono, T. Ozaki, S. Sakanaka, H. Sasaki, S. Sasaki, K. Satoh, M. Satoh, T. Shioya, T. Shishido, T. Suwada, M. Tadano, T. Takahashi, Y. Tanimoto, M. Tawada, M. Tobiyama, K. Tsuchiya, T. Uchiyama, K. Umemori, S. Yamamoto
  KEK, Ibaraki
• R. Hajima, H. Iijima, N. Kikuzawa, E. J. Minehara, R. Nagai, N. Nishimori, M. Sawamura
  JAEA/ERL, Ibaraki
• H. Hanaki, H. T. Tomizawa
  JASRI/SPring-8, Hyogo-ken
• A. Ishii, I. Ito, H. Kudoh, N. Nakamura, H. Sakai, S. Shibuya, K. Shinoe, H. Takaki
  ISSP/SRL, Chiba
• M. Katoh, A. Mochihashi, M. Shimada
  UVSOR, Okazaki

• M. Katoh
  
• K. Hayashi, M. Hosaka, A. Mochihashi, M. Shimada, J. Yamazaki
  UVSOR, Okazaki
• Y. Takashima
  Nagoya University, Nagoya

• T. Gowa
  
• H. Hayano, J. Urakawa
  KEK, Ibaraki
• Y. Kamiya, A. Masuda, R. Moriyama, K. Sakaue, M. Washio
  RISE, Tokyo
• S. Kashiwagi
  ISIR, Osaka
• R. Kuroda
  AIST, Tsukuba, Ibaraki
• K. U. Ushida
  RIKEN, Saitama

At Waseda University, we have succeeded in generating soft X-rays based on laser Compton scattering. The energies are within "Water Window" part (250~500eV) where the X-ray absorption coefficient of water is much less than that of constituent elements of living body such as carbon, hydrogen and nitrogen. For this reason, it is expected to apply to a bio-microscope with which we can observe living cells without dehydration. To improve the generation system, we remodeled our collision chamber and adopted 3-pass flash lamp amplifier system. With these modifications, we achieved high S/N ratio. The photon number detected by MCP was 278/pulse, tenfold increase of that in last year. Moreover, we succeeded in generating soft X-rays stably for more than 10 hours. Now we are planning to measure two-dimensional distribution of the X-rays by CCD. In this conference, experimental results and future plans will be reported.

• K. Sakaue
  
• S. Araki, M. K. Fukuda, Y. Higashi, Y. Honda, T. Taniguchi, N. Terunuma, J. Urakawa
  KEK, Ibaraki
• N. Sasao, H. Yokoyama
  Kyoto University, Kyoto
• M. Takano
  Tsukuba-shi, Ibaraki-ken
• M. Washio
  RISE, Tokyo

• R. Kuroda
  
• T. Gowa, Y. Kamiya, A. Masuda, R. Moriyama, K. Sakaue, M. Washio
  RISE, Tokyo
• S. Kashiwagi
  ISIR, Osaka
• M. K. Koike, H. Ogawa, N. Sei, H. Toyokawa, K. Y. Yamada, M. Y. Yasumoto
  AIST, Tsukuba, Ibaraki
• T. Nakajyo, F. Sakai, T. Y. Yanagida
  SHI, Tokyo

• Y.-C. Du
  
• W.-H. Huang, Y. Lin, C.-X. Tang, D. Xiang, L. X. Yan
  TUB, Beijing

This work was supported by the Chinese National Foundation of Natural Sciences under Contract no. 10645002.

• 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

• 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

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.

• L. X. Yan
  
• J. P. Cheng, Y.-C. Du, W.-H. Huang, Y. Lin, C.-X. Tang
  TUB, Beijing

The ultrashort ultraviolet (UV) laser system and the optical transport line for driving the photocathode RF gun at Accelerator Laboratory of Tsinghua University are introduced in the article. Temporal profile of the UV pulse was measured by non-colinear difference frequency generation (DFG) between the UV pulse itself and the jitter-free residual IR laser pulse after third harmonic generation (THG) process. Experiments to measure the dependence of quantum efficiency (QE) on laser polarization state are also performed. Results show that in our case the ratio of QE between p- and s- polarization is more than 2.6.

• J. H. Park
  
• J. Y. Huang, C. Kim, I. S. Ko, Y. W. Parc, S. J. Park
  PAL, Pohang, Kyungbuk
• D. Xiang
  TUB, Beijing

A high-brightness electron beam is emitted from a photo-cathode (PC) RF gun for use in the FIR (Far Infrared) facility being built at the Pohang Accelerator Laboratory (PAL). The beam dynamics study for the PAL XFEL injector is essencial to generate low emittance electron beam from the PC RF gun. The XFEL injector requires 1 nC beam with short bunch length and low emittance. This conditions are simulated with PARMELA code and then are realized on experimental conditions. The experimental conditions for the XFEL injector are measured with beam diagnostic devices such as ICT and Faraday cup for charge measurement, a spectrometer for beam energy measurement. In this article, we present the experimental approaches of the beam dynamics study for the XFEL injector.

wpjho@postech.ac.kr (Jangho Park)

• J. W. McKenzie
  
• B. L. Militsyn
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• A. S. Terekhov
  ISP, Novosibirsk

• P. H. Williams
  
• G. J. Hirst
  STFC/RAL, Chilton, Didcot, Oxon
• B. D. Muratori, H. L. Owen, S. L. Smith
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire

Studies of the electron beam dynamics for the 4GLS design are presented. 4GLS will provide three different electron bunch trains to a variety of user synchrotron sources. The 1 kHz XUV-FEL and 100 mA High Average Current branches share a common 540 MeV linac, whilst the 13 MHz IR-FEL must be well-synchronised to them. An overview of the injector designs, electron transport, and energy recovery is given, including ongoing studies of coherent synchrotron radiation, beam break-up and wakefields. This work is being pursued for the forthcoming Technical Design Report due in 2008.

• S. L. Smith
  
• N. Bliss
  STFC/DL, Daresbury, Warrington, Cheshire
• A. R. Goulden, G. Priebe
  STFC/DL/SRD, Daresbury, Warrington, Cheshire
• D. J. Holder, P. A. McIntosh
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire

• B. X. Yang
  
• E. M. Dufresne, E. C. Landahl, A. H. Lumpkin
  ANL, Argonne, Illinois

A short x-ray pulse source based on the crab cavity scheme proposed by Zholents* is being developed at the Advanced Photon Source (APS). Photon diagnostics that visualizes the electron bunches with transverse momentum chirp and verifies the performance of the short x-ray pulse is required. We present a design study for the imaging diagnostics inside and outside of the crab cavity zone, utilizing both x-ray and visible synchrotron radiation. Several design options of monochromatic and polychromatic x-ray optics will be explored for their compatibility with the short-pulse source. The diagnostics outside of the crab cavity zone will be used to map out stable operation parameters of the storage ring with crab cavities, and to perform single-bunch single-pass imaging of the chirped bunch, which facilitates the tuning of the crab cavity rf phase and amplitude so the performance of the short pulse source can be optimized while other users around the ring will not be disturbed.

* A. Zholents et al., NIM A 425, 385 (1999).

• 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

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.

• I. V. Pogorelov
  
• J. Qiang, R. D. Ryne, M. Venturini, A. Zholents
  LBNL, Berkeley, California
• R. L. Warnock
  SLAC, Menlo Park, California

• 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

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.

• C. Steier
  
• P. A. Heimann, S. Marks, D. Robin, R. W. Schoenlein, W. Wan
  LBNL, Berkeley, California
• W. Wittmer
  SLAC, Menlo Park, California

An upgraded femtosecond slicing facility has been commissioned successfully at the Advanced Light Source. In contrast to the original facility at the ALS which pioneered the concept, the new beamline uses an undulator (the first in-vacuum undulator at the ALS) as the radiator producing the user photon beam. To spatially separate the femtosecond slices in the radiator, a local vertical dispersion bump produced with 12 skew quadrupoles is used. The facility was successfully commissioned during the last 1.5 years and is now used in routine operation.

• E. J. Montgomery
  
• D. W. Feldman, N. A. Moody, P. G. O'Shea, Z. Pan
  UMD, College Park, Maryland
• K. Jensen
  NRL, Washington, DC

Photocathodes for high power free electron lasers face significant engineering and physics challenges in the quest for efficient, robust, long-lived, prompt laser-switched operation. The most efficient semiconductor photocathodes, notably those responsive to visible wavelengths, suffer from poor lifetime due to surface layer degradation, contamination, and desorption. Using a novel dispenser photocathode design, rejuvenation of cesiated surface layers in situ is investigated for semiconductor coatings building on previous results for cesiated metals. Cesium from a sub-surface reservoir diffuses to the surface through a microscopically porous, sintered tungsten matrix to repair the degraded surface layer. The goal of this research is to engineer and demonstrate efficient, robust, long-lived regenerable photocathodes in support of predictive photocathode modeling efforts and suitable for photoinjection applications.

• C. K. Sinclair
  
• I. V. Bazarov, B. M. Dunham, Y. Li, X. G. Liu, D. G. Ouzounov
  Cornell University, Department of Physics, Ithaca, New York
• F. E. Hannon
  Cockcroft Institute, Lancaster University, Lancaster
• T. Miyajima
  KEK, Ibaraki

Recent computational optimizations have demonstrated that it should be possible to construct electron injectors based on photoemission cathodes in very high voltage DC electron guns in which the beam emittance is dominated by the thermal emittance from the cathode. Negative electron affinity photocathodes have been shown to have a naturally low thermal emittance. However, the thermal emittance depends on the illuminating wavelength; the degree of negative affinity; and the band structure of the photocathode material. As part of the development of a high brightness, high average current photoemission electron gun for the injector of an ERL light source, we have measured the thermal emittance from negative affinity GaAs and GaAsP photocathodes. The measurements were made by measuring the electron beam spot size downstream of a counter-wound solenoid lens as a function of the lens strength. Electron beam spot sizes were measured by two techniques - a 20 micron wire scanner, and a CVD diamond screen. Both Gaussian and 'tophat' spatial profiles were used, and measurements were made at several wavelengths. Results will be presented for both cathode types.

• S. G. Anderson
  
• H. Badakov, P. Frigola, A. Fukasawa, B. D. O'Shea, J. B. Rosenzweig
  UCLA, Los Angeles, California
• C. P.J. Barty, D. J. Gibson, F. V. Hartemann, M. J. Messerly, M. Shverdin, C. Siders, A. M. Tremaine
  LLNL, Livermore, California

Compton scattering of intense laser pulses with ultra-relativistic electron beams has proven to be an attractive source of high-brightness x-rays with keV to MeV energies. This type of x-ray source requires the electron beam brightness to be comparable with that used in x-ray free-electron lasers and laser and plasma based advanced accelerators. We describe the development and commissioning of a 1.6 cell RF photoinjector for use in Compton scattering experiments at LLNL. Injector development issues such as RF cavity design, beam dynamics simulations, emittance diagnostic development, results of sputtered magnesium photo-cathode experiments, and UV laser pulse shaping are discussed. Initial operation of the photoinjector is described and transverse phase space measurements are presented.

• F. V. Hartemann
  
• S. G. Anderson, C. P.J. Barty, D. J. Gibson, C. Hagmann, M. Johnson, I. Jovanovic, D. P. McNabb, M. J. Messerly, J. A. Pruet, M. Shverdin, C. Siders, A. M. Tremaine
  LLNL, Livermore, California

A new class of tunable, monochromatic gamma-ray sources capable of operating at high peak and average brightness is currently being developed at LLNL for nuclear photo-science and applications. These novel systems are based on Compton scattering of laser photons by a high brightness relativistic electron beam produced by an rf photoinjector. Key technologies, basic scaling laws, and recent experimental results will be presented, along with an overview of future research and development directions.

• D. J. Gibson
  
• S. G. Anderson, C. P.J. Barty, S. M. Betts, F. V. Hartemann, I. Jovanovic, D. P. McNabb, M. J. Messerly, J. A. Pruet, M. Shverdin, C. Siders, A. M. Tremaine
  LLNL, Livermore, California

Thomson-Scattering based systems offer a path to high-brightness high-energy (> 1 MeV) x-ray & gamma-ray sources due to their favorable scaling with electron energy. LLNL is currently engaged in an effort to optimize such a device, dubbed the "Thomson-Radiated Extreme X-Ray" (T-REX) source, targeting up to 680 keV photon energy. Such a system requires precise design of the interaction between a high-intensity laser pulse and a high-brightness electron beam. Presented here are the optimal design parameters for such an interaction, including factors such as the collision angle, focal spot size, optimal bunch charge and laser intensity, pulse duration, and laser beam path. These parameters were chosen based on extensive modelling using PARMELA and in-house, well-benchmarked scattering simulation codes. Also discussed are early experimental results from the newly commissioned system.

• I. Jovanovic
  
• S. G. Anderson, C. P.J. Barty, C. G. Brown, D. J. Gibson, F. V. Hartemann, J. Hernandez, M. Johnson, D. P. McNabb, M. J. Messerly, J. A. Pruet, M. Shverdin, C. Siders, A. M. Tremaine
  LLNL, Livermore, California

Frequency upconversion of laser-generated photons by inverse Compton scattering for applications such as nuclear spectroscopy and gamma-gamma collider concepts on the future ILC would benefit from an increase of average source brightness. The primary obstacle to higher average brightness is the relatively small Thomson scattering cross section. It has been proposed that this limitation can be partially overcome by use of laser pulse recirculation. The traditional approach to laser recirculation entails resonant coupling of low-energy pulse train to a cavity through a partially reflective mirror.* Here we present an alternative, passive approach that is akin to "burst-mode" operation and does not require interferometeric alignment accuracy. Injection of a short and energetic laser pulse is achieved by placing a thin frequency converter, such as a nonlinear optical crystal, into the cavity in the path of the incident laser pulse. This method leads to the increase of x-ray/gamma-ray energy proportional to the increase in photon energy in frequency conversion. Furthermore, frequency tunability can be achieved by utilizing parametric amplifier in place of the frequency converter.

* G. Klemz, K. Monig, and I. Will, "Design study of an optical cavity for a future photon-collider at ILC", Nucl. Instrum. Meth. A 564, 212-224 (2006).

• 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

• A. Fukasawa
  
• S. G. Anderson
  LLNL, Livermore, California
• H. Badakov, E. Hemsing, B. D. O'Shea, J. B. Rosenzweig
  UCLA, Los Angeles, California

• 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

• J. T. Frederico
  
• G. Gatti
  INFN/LNF, Frascati (Roma)
• S. Reiche, R. Tikhoplav
  UCLA, Los Angeles, California

• S. Tochitsky
  
• C. Joshi, C. Sung
  UCLA, Los Angeles, California

Seeded FEL/IFEL techniques can be used for modulation of a relativistic electron beam longitudinally on the radiation wavelength. However, in the 1-10 THz range, which is of particular importance for matched injection of prebunched electrons into a laser-driven plasma accelerating structure, a suitable radiation source is not available. At the UCLA Neptune Laboratory we have built and fully characterized a radiation source tunable in the range of 1-3 THz. The THz pulse is produced by mixing two CO2 laser lines in a noncollinear phase-matched GaAs crystal at room temperature. The crystal is pumped by 200 ns pulses of a dual beam TEA CO2 laser running at 1 Hz. A grating placed in each lasing section allowed to cover the spectral range for the difference frequency from 0.5-4.5 THz with a step of 30-40 GHz. The achieved narrow bandwidth of ~10^-5 and the output power of 2kW are sufficient for seeding a single-pass, waveguide FEL amplifier-prebuncher*. These pulses were used to measure the coupling efficiency and the attenuation for different types of THz waveguides and the results will be reported.

* C. Sung et al. "Seeded FEL/IFEL techniques for radiation amplification and electron microbunching in the terahertz range" Phys. Rev. STAB, 2006 (to be published)

• 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

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.

• 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

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.

• Y. T. Ding
  
• P. Emma, Z. Huang
  SLAC, Menlo Park, California

* 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).

• 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

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.

• J. E. Spencer
  
• Y. A. Hussein
  SLAC, Menlo Park, California

This paper presents an efficient, RF-coupled, 95-GHz undulatory (snake-like) antenna that can be fabricated using IC technology. While there are many uses for directed power at this frequency our interest is in understanding the propagation of the input power through the circuit and its radiative characteristics for comparison to earlier work in the THz range (see PAC05). 95 GHz was chosen because test equipment was available (WR-10 waveguide and HP network analyzer). Different materials, heights and widths of the circuit were considered on a low-loss, 0.10-mm thick quartz substrate e.g. 0.75 microns of elevated gold corresponding to three skin depths. The design is compared to more conventional RF technology using a low energy, high power electron beam and to higher energy, lower power Smith Purcell gratings and free-electron-lasers (FELs). The FDTD results show narrow-band, 80% radiation efficiency with a dipole-like radiation pattern that is enhanced by adding periods. The radiated power was calculated using two different techniques that agreed quite well i.e. by integrating the far-field Poynting vector as well as subtracting the output power from input power.

• W. E. White
  
• J. Castro, P. Emma, A. Gilevich, C. Limborg-Deprey, H. Loos, A. Miahnahri
  SLAC, Menlo Park, California

• T. Plettner
  
• R. L. Byer
  Stanford University, Stanford, Califormia

• E. Pozdeyev
  

DC photoguns are used to produce high-quality, high-intensity electron beams for accelerator driven applications. Ion bombardment is credited as the major cause of degradation of the photocathode efficiency. Additionally to ions produced in the accelerating cathode-anode gap, the electron beam can ionize the residual gas in the transport line. These ions are trapped transversely within the beam and can drift back to the accelerating gap and contribute to the bombardment rate of the cathode. This paper proposes a method to reduce the flow of ions produced in the beam transport line and drifting back to the cathode-anode gap by introducing a positive potential barrier that repels the trapped ions. The reduced ion bombardment rate and increased life time of photocathodes will reduce the downtime required to service photoinjectors and associated costs.

• J. Smedley
  
• J. Iversen, D. Klinke, D. Kostin, W.-D. Moller, A. Muhs, J. S. Sekutowicz
  DESY, Hamburg
• P. Kneisel
  Jefferson Lab, Newport News, Virginia
• R. S. Lefferts, A. R. Lipski
  SBUNSL, Stony Brook, New York
• T. Rao
  BNL, Upton, Long Island, New York

We report recent progress in the development of a hybrid lead/niobium superconducting (SC) injector. The goal of this effort is to produce an all-SC injector with the SCRF properties of a niobium cavity along with the superior quantum efficiency (QE) of a lead photocathode. Two prototype hybrid injectors have been constructed, one utilizing a cavity with a removable cathode plug, and a second consisting of an all-niobium cavity arc-deposited with lead in the cathode region. We present the results of QE measurements on these cavities, along with tests of the effect of the laser on the cavity RF performance.

• T. Watanabe
  
• D. A. Harder, R. K. Li, J. B. Murphy, G. Rakowsky, Y. Shen, X. J. Wang
  BNL, Upton, Long Island, New York

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.

• 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

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).

• T. Morishita
  
• H. Asano, M. Ikegami
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• K. Hasegawa
  JAEA, Ibaraki-ken
• A. Ueno
  JAEA/LINAC, Ibaraki-ken

• T. Morishita
  
• H. Asano, M. Ikegami, T. Ito
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• K. Hasegawa
  JAEA, Ibaraki-ken
• F. Naito, E. Takasaki, H. Tanaka, K. Yoshino
  KEK, Ibaraki
• A. Ueno
  JAEA/LINAC, Ibaraki-ken

• J. Tamura
  
• T. Kanesue
  Kyushu University, Fukuoka
• M. Okamura
  BNL, Upton, Long Island, New York

• S. Kawata
  
• T. Kikuchi, M. Nakamura, Y. Nodera, N. Onuma
  Utsunomiya University, Utsunomiya

* R. Sonobe, S. Kawata, et. al., Phys. Plasmas 12 (2005) 073104.

• S. Banna
  
• V. Berezovsky, L. Schachter
  Technion, Haifa

Franck and Hertz in 1914 were the first to demonstrate that free electrons can be decelerated by mercury atoms in discrete energy quanta. In 1930 Latyscheff and Leipunsky have demonstrated the inverse effect namely; free electrons can be accelerated by energy stored in the mercury atoms (collision of the second kind). It was only in 1958 that Townes has used multiple collisions between photons and excited atoms to amplify radiation (MASER & LASER). In 1995 Schachter suggested to use excited atoms for coherently accelerate particles. The results of a proof-of-principle experiment (2006) demonstrating the PASER scheme are reported here. Performed at the BNL-ATF, the essence of the experiment is to inject a 45MeV density modulated beam into an excited CO2 gas mixture. Resonance is insured by having the beam bunched by its interaction with a high-power CO2 laser pulse within a wiggler. The electrons experienced 0.15% relative change in their kinetic energy, in less than 40cm long interaction region. The experimental results indicate that a fraction of these electrons have gained 200keV each, implying that such an electron has undergone 2,000,000 collisions of the second kind.

• C. M.S. Sears
  
• R. L. Byer, T. Plettner
  Stanford University, Stanford, Califormia
• E. R. Colby, R. Ischebeck, C. Mcguinness, R. Siemann, J. E. Spencer, D. R. Walz
  SLAC, Menlo Park, California

• M. J. Hogan
  
• I. Blumenfeld, F.-J. Decker, R. Ischebeck, R. H. Iverson, N. A. Kirby, R. Siemann, D. R. Walz
  SLAC, Menlo Park, California
• C. E. Clayton, C. Huang, C. Joshi, W. Lu, K. A. Marsh, W. B. Mori, M. Zhou
  UCLA, Los Angeles, California
• T. C. Katsouleas, P. Muggli, E. Oz
  USC, Los Angeles, California

The costs and the time scales of colliders intended to reach the energy frontier are such that it is important to explore new methods of accelerating particles to high energies. Plasma-based accelerators are particularly attractive because they are capable of producing accelerating fields that are orders of magnitude larger than those used in conventional colliders. In these accelerators a drive beam, either laser or particle, produces a plasma wave (wakefield) that accelerates charged particles. The ultimate utility of plasma accelerators will depend on sustaining ultra-high accelerating fields over a substantial length to achieve a significant energy gain. More than 42 GeV energy gain was achieved in an 85 cm long plasma wakefield accelerator driven by a 42 GeV electron drive beam at the Stanford Linear Accelerator Center (SLAC). Most of the beam electrons lose energy to the plasma wave, but some electrons in the back of the same beam pulse are accelerated with a field of ~52 GV/m. This effectively doubles their energy, producing the energy gain of the 3 km long SLAC accelerator in less than a metre for a small fraction of the electrons in the injected bunch.

• A. J. Gonsalves
  
• D. L. Bruhwiler, J. R. Cary
  Tech-X, Boulder, Colorado
• E. Cormier-Michel
  University of Nevada, Reno, Reno, Nevada
• E. Esarey, C. G.R. Geddes, W. Leemans, K. Nakamura, C. B. Schroeder, C. Toth
  LBNL, Berkeley, California
• S. M. Hooker
  OXFORDphysics, Oxford, Oxon

• C. G.R. Geddes
  
• J. R. Cary
  Tech-X, Boulder, Colorado
• E. Cormier-Michel
  University of Nevada, Reno, Reno, Nevada
• E. Esarey, W. Leemans, K. Nakamura, D. Panasenko, G. R.D. Plateau, C. B. Schroeder, C. Toth
  LBNL, Berkeley, California

Laser wakefield accelerators produce accelerating gradients up to hundreds of GeV/m and narrow energy spread, and have recently demonstrated energies up to GeV and improved stability [*,**] using electrons self trapped from the plasma. Controlled injection and staging can further improve beam quality by circumventing tradeoffs between energy, stability, and energy spread/emittance. We present experiments demonstrating production of a stable electron beam near 1 MeV with 100 keV level energy spread and central energy stability by using the plasma density profile to control self injection, and supporting simulations. A 10 TW laser pulse was focused near the downstream edge of a mm-long hydrogen gas jet. The plasma density near focus is decreasing in the laser propagation direction, which changes the wake phase velocity and reduces the trapping threshold. This allows stable self trapping and low absolute energy spread. Simulations indicate that such beams can be post accelerated to form high energy, high quality, stable beams, and experiments are under investigation.

* Geddes et al, Nature v431 no7008, 538 (2004).** Leemans et al, Nature Physics v2 no10, p696 (2006)

• C. E. Clayton
  
• F. Fang, C. Joshi, K. A. Marsh, A. E. Pak, J. E. Ralph
  UCLA, Los Angeles, California
• N. C. Lopes
  Instituto Superior Tecnico, Lisbon

In a laser wakefield accelerator experiment where the length of the pump laser pulse is several plasma period long, the leading edge of the laser pulse undergoes frequency downshifting as the laser energy is transferred to the wake. Therefore, after some propagation distance, the group velocity of the leading edge of of the pump pulse–and therefore of the driven electron plasma wave–will slow down. This can have implications for the dephasing length of the accelerated electrons and therefore needs to be understood experimentally. We have carried out an experimental investigation where we have measured the velocity v_f of the 'wave-front' of the plasma wave driven by a nominally 50fs (FWHM), intense (a₀~1), 0.8 micron laser pulse. To determine the speed of the wave front, time- and space-resolved shadowgraphy, interferometry, and Thomson scattering were used. Although low density data (n_e ~ 10¹⁸ cm^-3) showed no significant changes in v_f over 1.5mm (and no accelerated electrons), high-density data shows accelerated electrons and an approximately 5% drop in v_f after a propagation distance of about 800 microns.

• J. Urakawa
  

• A. Noda
  
• H. Fadil, M. Grieser
  MPI-K, Heidelberg
• M. Ikegami, T. Ishikawa, M. Nakao, T. Shirai, H. Souda, M. Tanabe, H. Tongu
  Kyoto ICR, Uji, Kyoto
• I. N. Meshkov, A. V. Smirnov
  JINR, Dubna, Moscow Region
• K. Noda
  NIRS, Chiba-shi

S-LSR is a storage and cooler ring with the circumference of 22.56 m applied for an electron beam cooling of 7 MeV proton beam and laser cooling of 24Mg+ beam with 35 keV. From the measurement with the use of Schottky pich-up of the momentum spread of 7 MeV proton beam reducing the particle number to suppress the effect of intra-beam scattering,abrupt jump in fractional momentum spread and Schottky power has been observed, which is considered the 1 dimensional phase transition to the ordered state*. The situation has also been expected from numerical simulation**. Laser cooling with much stronger cooling force is expected to realize 2Dand 3D crystalline states if the maintenance condition can be satisfied. Experimental approaches to realize such a condition at S-LSR as dispersion free lattice and "tapered cooling" are also decribed in the present paper.

* A Noda, et al., , New Journal of Physics, 8 (2006)288.** A. Smirnov et al., Beam Science and Technology, 10 (2006) 6*** J. Wei, X-P, Li and A. M. Sessler, , Phys. Rev. Lett. 73 (1994) 3089.

• P. N. Ni
  
• J. J. Barnard
  LLNL, Livermore, California
• F. M. Bieniosek, M. Leitner, B. G. Logan, R. More, P. K. Roy
  LBNL, Berkeley, California
• A. Fernengel, A. Menzel
  TU Darmstadt, Darmstadt
• A. Fertman, A. Golubev, B. Y. Sharkov, I. Turtikov
  ITEP, Moscow
• D. Hoffmann, A. Hug, N. A. Tahir, A. Udrea, D. Varentsov
  GSI, Darmstadt
• M. Kulish, D. Nikolaev, A. Ternovoy
  IPCP, Chernogolovka, Moscow region

• X. Chang
  
• I. Ben-Zvi, A. Burrill, J. G. Grimes, T. Rao, Z. Segalov, J. Smedley
  BNL, Upton, Long Island, New York
• Q. Wu
  IUCF, Bloomington, Indiana

• M. Hoffmann
  
• F. Ludwig, H. Schlarb, S. Simrock
  DESY, Hamburg

For pump- and probe experiments at VUV- and X-ray free-electron lasers the stability of the electron beam and timing reference must be guaranteed in phase for the injector and bunch compression section within a resolution of 0.01 degree (rms) and in amplitude within 1 10^-4 (rms). The performance of the field detection and regulation of the acceleration RF critically influences the phase and amplitude stability. For the RF field control, a multichannel RF downconverter is used to detect the field vectors and control the vectorsum of 32 cavities. In this paper a new design of an 8 channel downconverter is presented. The downconverter frontend consists of a passive rf double balanced mixer input stage, intermediate filters and an integrated 16bit analog-to-digital converter (ADC). The design includes a digital motherboard for data preprocessing and communication with the controller. In addition we characterize the downconverter performance in amplitude and phase jitter, temperature drifts and channel crosstalk in laboratory environment as well as for accelerator operation.

• K. Yokoyama
  
• Y. Higashi, T. Higo, N. K. Kudo, S. Ohsawa
  KEK, Ibaraki

• M. Taborelli
  
• G. Arnau-Izquierdo, S. Calatroni, S. T. Heikkinen, T. Ramsvik, S. Sgobba, W. Wuensch
  CERN, Geneva

• R. Akre
  
• J. M. Byrd
  LBNL, Berkeley, California
• D. Dowell, P. Emma, J. C. Frisch, B. Hong, K. D. Kotturi, P. Krejcik, J. Wu
  SLAC, Menlo Park, California

The Linac Coherent Light Source at SLAC will be the brightest X-ray laser in the world when it comes on line. In order to achieve the brightness a 100fS length electron bunch is passed through an undulator. To creat the 100fS bunch, a 10pS electron bunch, created from a photo cathode in an RF gun, is run off crest on the RF to set up a position to energy correlation. The bunch is then compressed chicanes. The stability of the RF system is critical in setting up the position to energy correlation. Specifications derived from simulations require the RF system to be stable to below 100fS in several critical injector stations and the last kilometer of linac. The SLAC linac RF system is being upgraded to meet these requirements.

• J. Guo
  
• S. G. Tantawi
  SLAC, Menlo Park, California

• W. Singer
  
• A. Brinkmann, A. Ermakov, J. Iversen, G. Kreps, A. Matheisen, D. Proch, D. Reschke, X. Singer, M. Spiwek, H. Wen
  DESY, Hamburg
• P. Kneisel
  Jefferson Lab, Newport News, Virginia
• M. Pekeler
  ACCEL, Bergisch Gladbach

• B. M. Hegelich
  

• V. V. Danilov
  
• A. V. Aleksandrov, S. Assadi, W. Blokland, S. M. Cousineau, C. Deibele, W. P. Grice, S. Henderson, J. A. Holmes, Y. Liu, M. A. Plum, A. P. Shishlo, A. Webster
  ORNL, Oak Ridge, Tennessee
• I. Nesterenko
  BINP SB RAS, Novosibirsk
• L. Waxer
  LJW, Saint Louis

Thin carbon foils are used as strippers for charge exchange injection into high intensity proton rings. However, the stripping foils become radioactive and produce uncontrolled beam loss, which is one of the main factors limiting beam power in high intensity proton rings. Recently, we presented a scheme for laser stripping an H^- beam for the Spallation Neutron Source ring. First, H^- atoms are converted to H0 by a magnetic field, then H0 atoms are excited from the ground state to the upper levels by a laser, and the excited states are converted to protons by a magnetic field. In this paper we report on the first successful proof-of-principle demonstration of this scheme to give high efficiency (around 90%) conversion of H^- beam into protons at SNS in Oak Ridge. The experimental setup is described, and comparison of the experimental data with simulations is presented. In addition, future plans on building a practical laser stripping device are discussed.

• L. Deacon, G. A. Blair, S. T. Boogert, A. Bosco, L. Corner, L. Deacon, N. Delerue, F. Gannaway, D. F. Howell, V. Karataev, M. Newman, A. Reichold, R. Senanayake, R. Walczak
  JAI, Egham, Surrey
• A. Aryshev, H. Hayano, K. Kubo, N. Terunuma, J. Urakawa
  KEK, Ibaraki
• G. E. Boorman
  Royal Holloway, University of London, Surrey
• B. Foster
  OXFORDphysics, Oxford, Oxon

The ATF extraction line laser-wire (LW) aims to achieve a micron-scale laser spot size and to verify that micron-scale beam profile measurements can be performed at the International Linear Collider beam delivery system. Recent upgrades to the LW system are presented together with recent results including the first use of the LW as a beam diagnostic tool.

• P. Musumeci
  
• J. Moody
  UCLA, Los Angeles, California

• L. Monaco
  
• J. W. Baehr, M. Krasilnikov, S. Lederer, F. Stephan
  DESY Zeuthen, Zeuthen
• J. H. Han, S. Schreiber
  DESY, Hamburg
• P. Michelato, C. Pagani, D. Sertore
  INFN/LASA, Segrate (MI)

The FLASH (DESY-Hamburg) and PITZ (DESY-Zeuthen) photoinjectors routinely use high quantum efficiency (QE) photocathodes produced at LASA (INFN-Milano), since 1998. To further understand the photocathode behavior during beam operation, photocathode QE measurements have been performed at different operating conditions in both RF photoinjectors. The analysis of these measurements will be used to improve the photocathode preparation procedures and to deeper understand the photocathode properties, whose final goal would be the further increase of their lifetime and beam quality preservation during the RF gun operations.

• F. Sakamoto
  
• M. Akemoto, T. Higo, J. Urakawa
  KEK, Ibaraki
• D. Ishida, N. Kaneko, H. Nose, H. Sakae, Y. Sakai
  IHI/Yokohama, Kanagawa
• T. Natsui, Y. Taniguchi, M. Uesaka, T. Yamamoto
  UTNL, Ibaraki
• M. Yamamoto
  Akita National College of Technology, Akita

• A. Sakumi
  
• Y. Muroya, T. Ueda, M. Uesaka
  The University of Tokyo, Nuclear Professional School, Ibaraki-ken

• A. Yamazaki
  
• T. Hosokai, K. Kinoshita, A. Maekawa, R. Tsujii, M. Uesaka, A. G. Zhidkov
  UTNL, Ibaraki

• M. Uesaka
  
• F. Sakamoto, A. Sakumi
  The University of Tokyo, Nuclear Professional School, Ibaraki-ken

• S. Kashiwagi
  
• R. Kato, J. Yang
  ISIR, Osaka
• R. Kuroda
  AIST, Tsukuba, Ibaraki
• K. Sakaue, M. Washio
  RISE, Tokyo
• J. Urakawa
  KEK, Ibaraki

*M. Goldstein et al., Proc. of the 27th Int. FEL conference, Stanford, California, USA (2005) pp.422-425**A. Endo, Sematic EUV source workshop, Barcelona, Spain (2006)

• T. Kondoh
  
• H. Kashima, J. Yang, Y. Yoshida
  ISIR, Osaka

• J. Yang
  
• K. Kan, T. Kondoh, Y. Yoshida
  ISIR, Osaka

• Y. Kamiya
  
• Y. Kato, A. Murata, K. Sakaue, M. Washio
  RISE, Tokyo
• N. Kudoh, M. Kuriki, T. T. Takatomi, N. Terunuma, J. Urakawa
  KEK, Ibaraki
• R. Kuroda
  AIST, Tsukuba, Ibaraki

• A. V. Tyukhtin
  
• S. N. Galyamin
  Saint-Petersburg State University, Saint-Petersburg

The possibility of using an active medium to amplify the generated wakefield of an electron beam and employing the amplified wakefield to accelerate a second beam has been recognized recently*. This acceleration scheme is one of several related methods referred to as the Particle Acceleration by Stimulated Emission of Radiation (PASER). However, only the case of an active medium with a single resonant frequency has been analyzed until now. In this paper we present the results of analytical and numerical studies of Cherenkov radiation (CR) in an active medium with two resonant frequencies. We show that this medium can amplify CR even in the case of a purely real refractive index. In contrast to a medium with a single resonant frequency the amplification effect takes place in the absence of metal boundaries but only for sufficiently strong restrictions on the parameters of the medium. The amplification can be effective even for a medium with a relatively small inversion. Examples of CR amplification are given for several active materials. The effect may be useful both for wakefield accelerators and Cherenkov detectors.

*L. Schachter, Phys. Rev., E, 62, 1252 (2000); N. V.Ivanov, A. V.Tyukhtin, Tech. Phys. Lett., 32, 449 (2006).

• H. Aksakal
  
• J. Resta-Lopez
  IFIC, Valencia
• F. Zimmermann
  CERN, Geneva

• S. P. Antipov
  
• M. E. Conde, W. Gai, J. G. Power, Z. M. Yusof
  ANL, Argonne, Illinois
• V. A. Dolgashev
  SLAC, Menlo Park, California
• L. K. Spentzouris
  Illinois Institute of Technology, Chicago, Illinois

A study of breakdown mechanism has been initiated at the Argonne Wakefield Accelerator Facility (AWA). Breakdown may include several factors such as local field enhancement, explosive electron emission, Ohmic heating, tensile stress produced by electric field, and others. The AWA is building a dedicated facility to test various models for breakdown mechanisms and to determine the roles of different factors in the breakdown. An imaging system is being put together to identify single emitters on the cathode surface. This will allow us to study dark current properties in the gun. We also plan to trigger breakdown events with a high-powered laser at various wavelengths (IR to UV). Another experimental idea follows from the recent work on a Schottky-enabled photoemission in an RF photoinjector that allows us to determine in situ the field enhancement factor on a cathode surface. Monitoring the field enhancement factor before and after can shed some light on a modification of metal surface after the breakdown.

• C. M. Bhat
  
• J.-P. Carneiro, R. P. Fliller, G. M. Kazakevich, J. K. Santucci
  Fermilab, Batavia, Illinois

Recently we have measured the transverse emittance using both multi-screen as well as muli-slit methods for a range of electron beam intensities from 1 nC to 4 nC at A0 Photoinjector facility at Fermilab. The data have been taken with un-stacked 2.5 ps laser pulse. In this paper we report on these measurements and compare the results with the predictions from beam dynamics calculations using ASTRA and General Particle Tracer including 3D space charge effects.

• C. Toth
  
• D. L. Bruhwiler, J. R. Cary
  Tech-X, Boulder, Colorado
• E. Esarey, C. G.R. Geddes, W. Leemans, K. Nakamura, D. Panasenko, C. B. Schroeder
  LBNL, Berkeley, California

Colliding laser pulses* have been proposed as a method for controlling injection of electrons into a laser wakefield accelerator (LWFA) and hence producing high quality relativistic electron beams with energy spread below 1% and normalized emittances below 1 micron. The original proposal relied on three coaxial pulsesI. One pulse excites a plasma wake, and a collinear pulse following behind it collides with a counterpropagating pulse forming a beat pattern that boosts background electrons into accelerating phase. A variation of this method uses only two laser pulses** which may be non-collinear. The first pulse drives the wake, and beating of the trailing edge of this pulse with the colliding pulse injects electrons. Non-collinear injection avoids optical elements on the electron beam path (avoiding emittance growth). We report on progress of non-collinear experiments at LBNL, using the Ti:Sapphire laser at the LOASIS facility of LBNL. Preliminary results indicate that electron beam properties are affected by the second beam. Details of the experiment will be presented.

* E. Esarey, et al, Phys. Rev. Lett 79, 2682 (1997).** G. Fubiani, Phys. Rev. E 70, 016402 (2004).

• K. Nakamura
  
• E. Esarey, C. G.R. Geddes, A. J. Gonsalves, W. Leemans, D. Panasenko, C. B. Schroeder, C. Toth
  LBNL, Berkeley, California
• S. M. Hooker
  OXFORDphysics, Oxford, Oxon

A GeV-class laser-driven plasma-based wakefield accelerator has been realized at the Lawrence Berkeley National Laboratory (LBNL). The device consists of a 100 TW-class high repetition rate Ti:sapphire LOASIS laser system of LBNL and a gas-filled capillary discharge waveguide developed at Oxford University. Results will be presented on the generation of GeV-class electron beams with a 3.3 cm long preformed plasma channel. The use of a discharge-based waveguide permitted operation at an order of magnitude lower density and 15 times longer distance than in previous experiments that relied on laser-preformed plasma channels. Laser pulses with peak power ranging from 10-50 TW were guided over more than 20 Rayleigh ranges and high-quality electron beams with energy up to 1 GeV were obtained. The dependence of the electron beam characteristics on plasma channel properties and laser parameters are discussed.

• W. Leemans
  
• E. Esarey, C. G.R. Geddes, N. H. Matlis, G. R.D. Plateau, C. B. Schroeder, C. Toth, J. Van Tilborg
  LBNL, Berkeley, California

At LBNL, laser wakefield accelerators (LWFA) now produce ultra-short electron bunches with energies up to 1 GeV[1]. As femtosecond electron bunches exit the plasma they radiate a strong burst in the terahertz range[2,3], via coherent transition radiation (CTR). Measuring the CTR properties allows non-invasive bunch-length diagnostics[4], a key to continuing rapid advance in LWFA technology. In addition, this method of CTR generation provides very high peak power that can lead novel THz-based applications. Experimental bunch length characterizations through electro-optic sampling as well as bolometric analysis are presented. Measurements demonstrate both the shot-by-shot stability of bunch parameters, and femtosecond synchronization between bunch, THz pulse, and laser beam.

[1] W. P. Leemans et al., Nature Physics 2, 696(2006)[2] W. P. Leemans et al., PRL 91, 074802(2003)[3] C. B. Schroeder et al., PRE 69, 016501(2004)[4] J. van Tilborg et al., PRL 96, 014801(2006)

• N. Vinogradov
  
• C. L. Bohn, P. Piot
  Northern Illinois University, DeKalb, Illinois
• J. W. Lewellen, J. Noonan
  ANL, Argonne, Illinois

• M. C. Thompson, H. Badakov, J. B. Rosenzweig, M. C. Thompson, G. Travish
  UCLA, Los Angeles, California
• M. J. Hogan, R. Ischebeck, N. A. Kirby, R. Siemann, D. R. Walz
  SLAC, Menlo Park, California
• P. Muggli
  USC, Los Angeles, California
• A. Scott
  UCSB, Santa Barbara, California
• R. B. Yoder
  Manhattan College, Riverdale, New York

The breakdown threshold of a dielectric subjected to the GV/m-scale electric-fields of an intense electron-beam has been measured. In this experiment at the Final Focus Test Beam (FFTB) facility, the 30 GeV SLAC electron beam was focused down and propagated through short fused-silica capillary-tubes with internal diameters of as little as 100 microns. The electric field at the inner surface of the tubes was varied from about 1 GV/m to 22 GV/m by adjusting the longitudinal compression of the electron bunch. The onset of breakdown, as indicated by a bright discharge, was found to correlate to a surface field of about 4 GV/m. An analysis of the damage sustained to the beam-exposed fibers, and its correlation to field amplitude, is also reported.

• J. B. Rosenzweig
  
• M. Bellaveglia, M. Boscolo, G. Di Pirro, M. Ferrario, D. Filippetto, G. Gatti, L. Palumbo, C. Vicario
  INFN/LNF, Frascati (Roma)
• L. Catani, A. Cianchi
  INFN-Roma II, Roma
• A. M. Cook, M. P. Dunning, R. J. England, P. Musumeci
  UCLA, Los Angeles, California
• S. M. Jones
  Jet Propulsion Laboratory, Pasadena, California

• W. Lu
  
• S. Fonseca, L. O. Silva, J. H. Vieira
  Instituto Superior Tecnico, Lisbon
• C. Joshi, W. B. Mori, F. S. Tsung, M. Tzoufras
  UCLA, Los Angeles, California

The extraordinary ability of space-charge waves in plasmas to accelerate charged particles at gradients that are orders of magnitude greater than that in current accelerators has been well documented. We develop a phenomenological framework for Laser Wakefield Acceleration (LWFA) in the 3D nonlinear regime, in which the plasma electrons are expelled by the radiation pressure of a short pulse laser, leading to nearly complete blowout. This theory provides a recipe for designing a LWFA for given laser and plasma parameters and estimates the number and the energy of the accelerated electrons whether self-injected or externally injected. These formulas apply for self-guided as well as externally guided pulses (e.g. by plasma channels). Based on this theory, we will present scenarios on how to build a single stage accelerator with output energies from GeV to TeV. Particle-In-Cell (PIC) simulations are used to verify our theory. This work was supported by DOE and NSF under grant Nos. DE-FG03-92ER40727, DE-FC02-01ER41179, DE-FG02-03ER54721, and NSF-Phy-0321345.

• J. E. Ralph
  
• C. E. Clayton, F. Fang, C. Joshi, K. A. Marsh, A. E. Pak
  UCLA, Los Angeles, California

High-intensity short-pulse laser guiding in plasma channels has extended the length over which acceleration occurs in laser wake field accelerators*. Recent multidimensional nonlinear plasma wave theory predicts a range of optimal characteristics for self-guiding of laser pulses in the blowout regime for pulses shorter than a plasma wavelength**. This theory predicts a robust, stable parameter space for self-guiding and wake production and has been verified through multidimensional particle-in-cell simulations. We experimentally explore the plasma dynamics and laser pulse propagation using a 50 fs multi-terawatt Ti:Sapphire laser in a helium plasma at plasma densities, laser powers, and spot sizes within this parameter space. Our parameters are in the range where the plasma is underdense and the laser power is much greater than the critical power for self focusing. The evolution of the laser pulse and plasma channel will be followed over several Rayleigh lengths.

* C. Geddes et. al., Nature (London) 431, 538 (2004)** W. Lu et. al., Phys. Plasmas 13, 056709 (2006)

• R. Tikhoplav
  
• J. T. Frederico, G. Reed, J. B. Rosenzweig, S. Tochitsky, G. Travish
  UCLA, Los Angeles, California
• G. Gatti
  INFN/LNF, Frascati (Roma)

• M. Tzoufras
  
• S. Fonseca, L. O. Silva, J. H. Vieira
  Instituto Superior Tecnico, Lisbon
• C. Huang, W. Lu, W. B. Mori, F. S. Tsung
  UCLA, Los Angeles, California

The realization of high quality LWFA-produced electron beams requires laser pulses that remain focused for distances exceeding the Rayleigh length. It is often thought that a short pulse laser cannot be self-guided and some form of external optical guiding is needed. As short pulse lasers with higher power are rapidly coming online to test the LWFA concept it is vital to understand the nature of their propagation through centimeters of plasma. We argue that a degree of self-guiding is possible for short ultra-intense pulses that have been shown to lead to complete ponderomotive expulsion of plasma electrons. Furthermore, the generation of a high quality electron beam requires proper loading of the wake. We have developed a theoretical framework which predicts the maximum number of electrons which can be loaded in the wake, as well as the optimal charge density profile for beam loading. Using the PIC codes OSIRIS and QuickPIC we present designs of LWFA accelerators that verify our theoretical estimates as well as demonstrate the potential of LWFA to produce high energy electron beams with high beam quality.

• C. M.S. Sears
  
• R. L. Byer, T. Plettner
  Stanford University, Stanford, Califormia
• E. R. Colby, B. M. Cowan, R. Ischebeck, C. Mcguinness, R. J. Noble, R. Siemann, J. E. Spencer, D. R. Walz
  SLAC, Menlo Park, California

• J. E. Spencer
  
• E. R. Colby, R. Ischebeck, D. J. McCormick, C. Mcguinness, J. Nelson, R. J. Noble, C. M.S. Sears, R. Siemann
  SLAC, Menlo Park, California
• T. Plettner
  Stanford University, Stanford, Califormia

The NLC Test Accelerator (NLCTA) at SLAC was built to address various beam dynamics issues for the Next Linear Collider. An S-Band RF gun has been installed with diagnostics and a low energy spectrometer (LES) at 6 MeV together with a large-angle extraction line at 60 MeV. This is followed by a matching section, buncher and final focus for the laser acceleration experiment, E163. The laser-electron interaction area is followed by a broad range (2\%), high resolving power (10⁴) spectrometer (HES) for electron bunch analysis. Emittance compensating solenoids and the LES are used to tune for best operating point and match to the linac. Optical symmetries in the design of the 25.5^° extraction line provide 1:1 phase space transfer without use of sextupoles for a large, 6D phase space volume and range of input conditions. Spot sizes of a few microns at the IP (or HES object) allow tests of microscale structures as well as high resolving power at the image of the HES. Tolerances, tuning sensitivities and diagnostics are discussed together with the latest commissioning results and their comparison to design expectations.

• W. D. Zacherl
  
• E. R. Colby, C. Mcguinness
  SLAC, Menlo Park, California
• T. Plettner
  Stanford University, Stanford, Califormia

The E163 laser acceleration experiments conducted at SLAC have stringent requirements on the temporal properties of two regeneratively amplified, 800nm, Spitfire laser systems. To determine the magnitude and cause of timing instabilities between the two Ti:Sapphire amplifiers, we pass the two beams through a cross-correlator and focus the combined beam onto a Hamamatsu G1117 photodiode. The photodiode has a bandgap such that single photon processes are suppressed and only the second order, two-photon process produces an observable response. The response is proportional to the square of the intensity. The diode is also useful as a diagnostic to determine the optimal configuration of the compression cavity.

Yoshihiro Takagi et al, 'Multiple- and Single-shot autocorrelator based on two-photon conductivity in semiconductors.' Optics Letters, Vol. 17, No. 9, May 1, 1992.

• J. M. Grames
  
• P. A. Adderley, J. Brittian, J. Clark, J. Hansknecht, D. Machie, M. Poelker, M. L. Stutzman, R. Suleiman, K. E.L. Surles-Law
  Jefferson Lab, Newport News, Virginia

A new 100 kV GaAs DC Load Lock Photogun has been constructed at Jefferson Laboratory, with improvements for photocathode preparation and for operation in a high voltage, ultra-high vacuum environment. Although difficult to gauge directly, we believe that the new gun design has better vacuum conditions compared to the previous gun design, as evidenced by longer photocathode lifetime, that is, the amount of charge extracted before the quantum efficiency of the photocathode drops by 1/e of the initial value via the ion back-bombardment mechanism. Photocathode lifetime measurements at DC beam intensity of up to 10 mA have been performed to benchmark operation of the new gun and for fundamental studies of the use of GaAs photocathodes at high average current*. These measurements demonstrate photocathode lifetime longer than one million Coulombs per square centimeter at a beam intensity higher than 1 mA. The photogun has been reconfigured with a high polarization strained superlattice photocathode (GaAs/GaAsP) and a mode-locked Ti:Sapphire laser operating near band-gap. Photocathode lifetime measurements at beam intensity greater than 1 mA are measured and presented for comparison.

"Further Measurements of Photocathode Operational Lifetime at Beam Intensity >1mA using the CEBAF 100 kV DC GaAs Photogun", J. Grames et al., Proc. of the 17th Inter. Spin Symposium, Japan (2006).

• V. B. Graves
  
• A. J. Carroll, P. T. Spampinato
  ORNL, Oak Ridge, Tennessee
• I. Efthymiopoulos, A. Fabich
  CERN, Geneva
• H. G. Kirk, H. Park, T. Tsang
  BNL, Upton, Long Island, New York
• K. T. McDonald
  PU, Princeton, New Jersey
• P. Titus
  MIT/PSFC, Cambridge, Massachusetts

The design and operational testing of a mercury jet delivery system is presented. The equipment is part of the Mercury Intense Target (MERIT) Experiment, which is a proof-of-principle experiment to be conducted at CERN in the summer of 2007 to determine the feasibility of using an unconstrained jet of mercury as a target in a Neutrino Factory or Muon Collider. The Hg system is capable of producing a 1 cm diameter, 20 m/s jet of Hg inside a high-field solenoid magnet. A high-speed optical diagnostic system allows observation of the interaction of the jet with a 24 GeV proton beam. Performance of the Hg system will be presented, along with results of integrated systems testing without a beam.

• R. B. Yoder
  
• J. B. Rosenzweig, G. Travish
  UCLA, Los Angeles, California

*R. Yoder and J. Rosenzweig, Phys. Rev. STAB 8, 111301 (2005); Z. Zhang et al., Phys. Rev. STAB 8, 071302 (2005); A. Mizrahi and L. Schachter, Phys. Rev. E 70, 016505 (2004).

• C.-J. Jing
  
• M. E. Conde, W. Gai, J. G. Power, Z. M. Yusof
  ANL, Argonne, Illinois
• A. Kanareykin, P. Schoessow
  Euclid TechLabs, LLC, Solon, Ohio

Based on our previous experiment that successfully demonstrated wakefield transformer ratio enhancement in a 13.625 GHz dielectric-loaded collinear wakefield accelerator using the ramped bunch train technique, we present here a redesigned experimental scheme for even higher enhancement of the efficiency of this accelerator. Design of a collinear wakefield device with a transformer ratio R>>2, is presented. Using a ramped bunch train (RBT) rather than a single drive bunch, the enhanced transformer ratio (ETR) technique is able to increase the transformer ratio R above the ordinary limit of 2. To match the wavelength of the fundamental mode of the wakefield with the bunch length (σz=2 mm) of the new Argonne Wakefield Accelerator (AWA) drive gun, where the experiment will be performed, a 26.625 GHz dielectric based accelerating structure is required. This transformer ratio enhancement technique based on our dielectric-loaded waveguide design will result in a compact, high efficiency accelerating structure for future wakefield accelerators.

• T. Plettner
  
• R. L. Byer
  Stanford University, Stanford, Califormia
• E. R. Colby, R. Ischebeck, C. Mcguinness, R. J. Noble, C. M.S. Sears, R. Siemann, J. E. Spencer, D. R. Walz
  SLAC, Menlo Park, California

• T. Plettner
  
• R. L. Byer, P. P. Lu
  Stanford University, Stanford, Califormia

• I. Pogorelsky
  
• V. Yakimenko
  BNL, Upton, Long Island, New York

Compton interaction point incorporated into a high-average-power laser cavity is the key element of the Polarized Positron Source (PPS) concept proposed for ILC [1]. According to this proposal, circularly polarized gamma rays are produced in Compton backscattering from a 6 GeV linac e-beam inside a CO2 laser amplifier cavity. Intra-cavity positioning of the interaction point allows multiple laser recycling to match the electron bunch train format. We conducted experimental tests of multi-pulse operation of such active Compton cavity upon injection of a picosecond CO2 laser beam. Together with earlier demonstration of a high x-ray yield via the e-beam/CO2-laser backscattering, these new results show a viability of the entire PPS concept and closely prototype the laser source requirements for ILC.

[1] V. Yakimenko and I. V. Pogorelsky, Phys. Rev. ST Accel. Beams 9, 091001 (2006)

• D. Kaganovich
  
• D. F. Gordon, A. Ting
  NRL, Washington, DC

• S. Schnepp
  
• E. Gjonaj, T. Weiland
  TEMF, Darmstadt

For the coupled simulation of charged particles and electromagnetic fields several techniques are known. In order to achieve accurate results various parameters have to be taken into account. The number of macro-particles per cell, the resolution of the computational grid, and other parameters strongly affect the accuracy of the results. In the code tamBCI, based on a time-adaptive mesh, additional variables related to the adaptive grid refinement have to be chosen appropriately. An analysis of these values is carried out and the results are applied to the self-consistent simulation of the injector section of FLASH in 3D.

• A. Bacci
  
• V. Petrillo
  Universita' degli Studi di Milano, Milano
• A. R. Rossi, L. Serafini
  INFN-Milano, Milano

• S. Liu
  
• S. Araki, M. K. Fukuda, M. Takano, N. Terunuma, J. Urakawa
  KEK, Ibaraki
• K. Hirano
  NIRS, Chiba-shi

• J. C.T. Thangaraj
  
• G. Bai, B. L. Beaudoin, S. Bernal, D. W. Feldman, R. B. Fiorito, I. Haber, R. A. Kishek, P. G. O'Shea, M. Reiser, D. Stratakis, D. F. Sutter, K. Tian, M. Walter
  UMD, College Park, Maryland

The University of Maryland Electron Ring (UMER) is a scaled model to investigate the transverse and longitudinal physics of space charge dominated beams. It uses a 10-keV electron beam along with other scaled beam parameters that model the larger machines but at a lower cost. Understanding collective behavior of intense, charged particle beams due to their space charge effects is crucial for advanced accelerator research and applications. This paper presents the experimental study of longitudinal dynamics of an initial density modulation on a spacecharge dominated beam. A novel experimental technique of producing a perturbation using a laser is discussed. Using a laser to produce a perturbation provides the ability to launch a pure density modulation and to have better control over the amount of perturbation introduced. Collective effects like space charge waves and its propagation over long distances in a quadrupole channel are studied. One dimensional cold fluid model is used for theoretical analysis and simulations are carried out in WARP-RZ.

• M. Chung
  
• R. C. Davidson, P. Efthimion, E. P. Gilson, R. M. Majeski
  PPPL, Princeton, New Jersey

Installation of a laser-induced fluorescence (LIF) diagnostic system has been completed and initial measurement of the beam density profile has been performed on the Paul trap simulator experiment (PTSX). The PTSX device is a linear Paul trap that simulates the collective processes and nonlinear transverse dynamics of an intense charged particle beam propagating through a periodic focusing quadrupole magnetic configuration. Although there are several visible transition lines for the laser excitation of barium ions, the transition from the metastable state has been considered first mainly because an operating, stable, broadband, and high-power laser system is available for experiments in this region of the red spectrum. The LIF system is composed of a dye laser, fiber optic cables, a line generator, which uses a Powell lens, collection optics, and a CCD camera system. Single-pass mode operation of the PTSX device is employed for the initial tests of the LIF system to make optimum use of the metastable ions. By minimizing the background light level, it is expected that enough signal to noise ratio can be obtained to re-construct the radial density profile of the ion beam.

• M. Poelker
  
• P. A. Adderley, J. Brittian, J. Clark, J. M. Grames, J. Hansknecht, J. McCarter, M. L. Stutzman, R. Suleiman, K. E.L. Surles-Law
  Jefferson Lab, Newport News, Virginia

• M. Okamura
  
• A. Kondrashev
  ANL, Argonne, Illinois

Laser beams have been widely used in the accelerator field for various applications. Here, we focus on ion beam production usage as an ion source. The laser ion source (LIS) already has about thirty years history and was developed for providing pulsed beam to synchrotrons. Since 2000 we have concentrated on the use of the high brightness of induced laser plasma to provide intense highly charged ions efficiently. To take advantage of the intrinsic density of the plasma, Direct Plasma Injection Scheme (DPIS) has been developed. The induced laser plasma has initial expanding velocity and can be delivered directly to the RFQ. The presentation will discuss general features of the laser ion sources and advantages of the DPIS.

• F. Loehl
  
• J. Chen, F. X. Kaertner, J. Kim, F. Wong
  MIT, Cambridge, Massachusetts
• J. M. Mueller
  TUHH, Hamburg
• H. Schlarb
  DESY, Hamburg

• R. B. Wilcox
  
• J. W. Staples
  LBNL, Berkeley, California

Development of accelerator-based light sources is expanding the size of femtosecond laser systems from tabletop devices up to kilometer-scale facilities. New optical techniques are needed to maintain temporal stability in these large systems. We present methods for distributing timing information over optical fiber using continuous optical waves, and how these can be employed in advanced accelerators requiring less than 100fs timing stability. Different techniques combine to form a tool set that can provide for synchronization down to a few femtoseconds. Practical examples are given for timing systems applicable to FELs now under construction, with experimental results to show these systems can be built with required performance. For example, have demonstrated 2km fiber links with 5fs timing stability over 24 hours, and synchronized femtosecond lasers separated by a fiber link with 20fs RMS relative jitter.

• W. R. Flavell
  

* e.g. J Andruszkow et al., Phys. Rev. Lett., 85, 3825, (2000).**e.g. G. R. Neil et al., Phys. Rev. Lett. 84, 662, (2000).*** e.g. H Wabnitz et al., Nature, 420, 467, (2002), T Laarmann et al., Phys. Rev. Lett., 95, 063402 (2005)

• C. Joshi
  

• N. Baboi
  
• P. Castro, O. Hensler, J. Lund-Nielsen, D. Noelle, L. M. Petrosyan, E. Prat, T. Traber
  DESY, Hamburg
• M. Krasilnikov, W. Riesch
  DESY Zeuthen, Zeuthen

• R. Tsujii
  
• T. Hosokai
  RLNR, Tokyo
• K. Kinoshita, Y. Kondo, A. Maekawa, Y. Shibata, M. Uesaka, A. Yamazaki
  UTNL, Ibaraki
• T. Takahashi
  KURRI, Osaka
• A. G. Zhidkov
  Central Research Institute of Electric Power Industry, Komae

• W. W. Zhang
  
• Y. Li
  CAEP, Mainyang, Sichuan

• M. T. Price
  
• K. Balewski, Eckhard. Elsen, V. Gharibyan, H.-C. Lewin, F. Poirier, S. Schreiber, N. J. Walker, K. Wittenburg
  DESY, Hamburg
• G. A. Blair, S. T. Boogert, G. E. Boorman, A. Bosco, S. Malton
  Royal Holloway, University of London, Surrey
• T. Kamps
  BESSY GmbH, Berlin

The current PETRA II Laser-Wire system, being developed for the ILC and PETRA III, uses a piezo-driven mirror to scan laser light across an electron bunch. This paper reports on the recently installed electron-beam finding system, presenting recent horizontal and vertical profile scans with corresponding studies.

• S. R. Babel
  

High voltage power modules find uses in many applications like the Photo multiplier Tubes (PMT), Ionization chambers, CRT systems testing, high voltage biasing for Avalanche Photodiodes, Photo detectors, X-ray tubes, Pulse generators which are used in radars, lasers, EMC testing and other imaging applications. Providing high voltage, to these applications, which can be remotely controlled in a small, confined area, is a problem many laboratories around the world face. The LV and the HV series of high voltage systems from BiRa Systems present experimenters with voltages ranging from several hundreds upto ± 5kV in a rugged CompactPCI / PXI chassis, running National Instruments' LabView. The CompactPCI architecture offers modularity, tight integration and low cost. Apart from that, the deterministic and real time nature of the operating system also allows these modules to be remotely controlled and monitored over the Ethernet. The high voltage cards can be easily custom tailored to a particular voltage and current requirement

• J. G. Power
  
• M. E. Conde, W. Gai, F. Gao, R. Konecny, W. Liu, Z. M. Yusof
  ANL, Argonne, Illinois
• P. Piot, M. M. Rihaoui
  Northern Illinois University, DeKalb, Illinois

• J. Ruan
  
• H. Edwards, V. E. Scarpine, C.-Y. Tan, R. Thurman-Keup
  Fermilab, Batavia, Illinois
• YL. Li, J. G. Power
  ANL, Argonne, Illinois
• T. J. Maxwell
  Northern Illinois University, DeKalb, Illinois

The free space electro-optical (EO) sampling technique is a powerful tool for analyzing the longitudinal charge density of an ultrashort e-beam. In this paper, we present

1. experimental results for a laser-based mock-up of the EO experiment* and
2. a design for a beam-based, single-shot, EO sampling experiment using the e-beam from the Argonne Wakefield Accelerator (AWA) RF photoinjector.

* Yuelin Li, Appl. Phys. Lett. 88, 251108, 2006

• S. De Santis
  
• J. M. Byrd, R. B. Wilcox
  LBNL, Berkeley, California
• Y. Yin
  Y. Y. Labs, Inc., Fremont, California

We present the results of an experimental study of a beam timing monitor based on a technique demonstrated by Loehl*. This technique uses the electrical signal from a beam position monitor to amplitude-modulate a train of laser pulses, converting timing jitter into an amplitude jitter. This modulation is then measured with a photodetector and sampled by a fast ADC. This approach has already demonstrated sub-100 fsec resolution and promises even better results. Our study focuses on the use of this technique for precision timing for storage rings. We show results of measurements using signals from the Advanced Light Source.

* F. Loehl, et al., Proc. of the 2006 EPAC., p. 2781.

• J. Qiang
  
• J. M. Byrd, J. Feng, G. Huang
  LBNL, Berkeley, California

Streak camera is an important diagnostic device in the studies of laser plasma interaction, the detailed structure of photo reaction from material science to biochemistry, and in the measurement of the longitudinal distribution of a beam in accelerators. In this paper, we report on a new method which can potentially improve the temporal resolution of a streak camera down to femtoseconds. This method uses a time-dependent acceleration field to defocus the photo electrons longitudinally. This not only reduces the time dispersion distortion caused by initial energy spread but also mitigates the effects from the space-charge forces. An illustration of the method shows significant improvement of the modulation transfer function (MFT) compared with the conventional design.

• T. J. Maxwell
  
• C. L. Bohn, D. Mihalcea, P. Piot
  Northern Illinois University, DeKalb, Illinois

Electrons impinging on a thin metallic foil are seen to deliver small bursts of transition radiation (TR) as they cross the boundary from one medium to the next. A popular diagnostic application is found for compact electron bunches. In this case they will emit radiation more or less coherently with an N-squared enhancement of the intensity on wavelengths comparable to the bunch size, generating coherent transition radiation (CTR). Several detailed analytical descriptions have been proposed for describing the resulting spectral distribution, often making different simplifying assumptions. Given that bunches tenths of millimeters long can generate measurable spectra into the millimeter range, concern may arise as to weak diffraction effects produced by optical interference devices containing elements with dimensions in the centimeter range. The work presented here is a report on an upcoming graduate thesis exploring these effects as they apply to the Fermilab/NICADD photoinjector laboratory using a minimal C++ code that implements the methods of virtual quanta and vector diffraction theory.

• M. M. Rihaoui
  
• C. L. Bohn, P. Piot
  Northern Illinois University, DeKalb, Illinois
• J. G. Power
  ANL, Argonne, Illinois

• C. Sun
  
• Y. K. Wu
  FEL/Duke University, Durham, North Carolina

• Y. Yin
  
• X. Che
  Y. Y. Labs, Inc., Fremont, California
• J. H. Wang, K. Zheng
  USTC/NSRL, Hefei, Anhui

• S. Walston
  
• S. T. Boogert
  Royal Holloway, University of London, Surrey
• C. C. Chung, P. Fitsos, J. Gronberg
  LLNL, Livermore, California
• J. C. Frisch, S. Hinton, J. May, D. J. McCormick, S. Smith, T. J. Smith, G. R. White
  SLAC, Menlo Park, California
• H. Hayano, Y. Honda, N. Terunuma, J. Urakawa
  KEK, Ibaraki
• Yu. G. Kolomensky, T. Orimoto
  UCB, Berkeley, California
• P. Loscutoff
  LBNL, Berkeley, California
• A. Lyapin, S. Malton, D. J. Miller
  UCL, London
• R. Meller
  Cornell University, Department of Physics, Ithaca, New York
• M. C. Ross
  Fermilab, Batavia, Illinois
• M. Slater, M. Thomson, D. R. Ward
  University of Cambridge, Cambridge
• V. Vogel
  DESY, Hamburg

• R. J. England
  
• D. Alesini
  INFN/LNF, Frascati (Roma)
• B. D. O'Shea, J. B. Rosenzweig, G. Travish
  UCLA, Los Angeles, California

A 9-cell standing wave deflecting cavity has recently been constructed and installed at the UCLA Neptune Laboratory for use as a temporal diagnostic for the 13 MeV, 300 to 700 pC electron bunches generated by the Neptune photoinjector beamline. The cavity is a center-fed Glid-Cop structure operating in at TM110-like deflecting mode at 9.59616 GHz with a pi phase advance per cell. At the maximum deflecting voltage of 500 kV, the theoretical resolution limit of the device is 50 fs, although with current beam parameters and a spot size of 460 microns RMS the effective resolution is approximately 400 fs. We discuss the operation and testing of the cavity as well as its intended application: measuring the temporal current profile of ramped electron bunches generated using the Neptune dogleg compressor, and we present the first measurements of the electron beam current profile obtained using the deflecting cavity.

• C. Mcguinness
  
• R. L. Byer, T. Plettner
  Stanford University, Stanford, Califormia
• E. R. Colby, R. Ischebeck, R. J. Noble, C. M.S. Sears, R. Siemann, J. E. Spencer, D. R. Walz
  SLAC, Menlo Park, California

The laser acceleration experiments conducted for the E163 project at the NLC Test Accelerator facility at SLAC have stringent requirements on the temporal properties of the electron and laser beams. A system has been implemented to measure the relative phase stability between the RF sent to the gun, the RF sent to the accelerator, and the laser used to generate the electrons. This system shows rms timing stability better than 1 psec. Temporal synchronicity between the 0.5 psec electron bunch, and the 0.5 psec laser pulse is also of great importance. Cherenkov radiation is used to measure the arrival time of the electron bunch with respect to the laser pulse, and the path length of the laser transport is adjusted to optimize temporal overlap. A linear stage mounted onto a voice coil is used to make shot-by-shot fine timing adjustments to the laser path. The final verification of the desired time stability and control is demonstrated by observing the peak of the laser-electron interaction signal over the course of several minutes.