• L. Merminga
  

• S. Ohsawa
  
• Y. Hozumi
  Advanced Manufacturing Research Institute, Tsukuba
• M. Ikeda, T. Sugimura
  KEK, Ibaraki

• H. Ohgaki
  
• T. Kii, K. Masuda, T. Yamazaki, K. Yoshikawa, H. Zen
  Kyoto IAE, Kyoto

• J. Dedic
  
• D. Golob, A. Hasanovic, M. Plesko
  Cosylab, Ljubljana

• C. Y. Wu
  
• J. Chen, K. T. Hsu, S. Y. Hsu, J.-Y. Hwang, D. Lee, K.-K. Lin, C.-J. Wang
  NSRRC, Hsinchu

• 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.

• C. H. Rivetta
  
• R. Akre, P. Cutino, J. C. Frisch, K. D. Kotturi
  SLAC, Menlo Park, California

The LCLC RF gun requires a water cooling thermal system to tune the resonance frequency of the cavity to 2856.03MHz. The RF system operates in pulsed mode with bursts of 2.5usec at a repetition rate of 30-120Hz. The thermal system operates in combination with the low-level RF system to set the operation point of the cavity. The Low-Level RF system controls the magnitude and phase of the cavity voltage and define slow signals to the thermal system. The thermal system operates by pre-heating / pre-cooling the water and mixing both channels to achieve the optimal temperature to control the cavity resonant frequency. The tune control of the RF gun include two systems with different dynamics. The dynamics of the thermal system is slow while the RF system is fast. Additionally, different actuators in the system present limits that introduce non-linearities to be taking into account during the start up process . Combining these characteristics, a controller is designed for the resulting hybrid system that allows convergence in large for all the operation conditions and achieve the performance in the magnitude and phase of the cavity voltage required around the operation point.

• J. E. Spencer
  

We consider optimization of the generalized luminosity per unit cost of a linear collider in this ES&H era. Examples running over the length of the LC, starting at the source and ending at the dump, suggest that both costs (capital and operating) and environmental issues can be improved in a compatible way. Thus, a RoHS by any other name (WEES or OSHA) need not present thorny problems requiring unexpected R&D but a push to leverage many recent advances that might otherwise be overlooked or avoided. The physics is interesting and the true amortized cost may be seriously underestimated by ignoring such issues. For example, the entire, interior surface of a laser driven RF gun involves interesting materials science where the space requires continuous UHV to sustain stable, acceptable quantum efficiency as well as avoid RF breakdown damage in an environment that is also subject to radiation damage. All of these can seriously reduce a gun's output and LCs luminosity. Intelligent design of rad-hard systems can approach the ideal of bug-proof software that needn't produce overly slow or ponderous systems while providing opportunities to innovate that justify the costs.

• 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. 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.

• Z. Li
  
• V. Akcelik, A. E. Candel, L. Ge, A. C. Kabel, K. Ko, L. Lee, C.-K. Ng, E. E. Prudencio, G. L. Schussman, R. Uplenchwar, L. Xiao
  SLAC, Menlo Park, California

Under the support of the U. S. DOE SciDAC program, SLAC has been developing a suite of 3D parallel finite-element codes aimed at high-accuracy, high-fidelity electromagnetic and beam physics simulations for the design and optimization of next-generation particle accelerators. Running on the latest supercomputers, these codes have made great strides in advancing the state of the art in applied math and computer science at the petascale that enable the integrated modeling of electromagnetics, self-consistent Particle-In-Cell (PIC) particle dynamics as well as thermal, mechanical, and multi-physics effects. This paper will present 3D results of trapped mode calculations in an ILC cryomodule and the modeling of the ILC Sheet Beam klystron, shape determination of superconducting RF (SCRF) cavities and multipacting studies of SCRF HOM couplers, as well as 2D and preliminary 3D PIC simulation results of the LCLS RF gun.

• A. E. Candel
  
• A. C. Kabel, K. Ko, L. Lee, Z. Li, C. Limborg-Deprey, C.-K. Ng, E. E. Prudencio, G. L. Schussman, R. Uplenchwar
  SLAC, Menlo Park, California

Over the past years, SLAC's Advanced Computations Department (ACD) has developed the parallel finite element particle-in-cell code Pic3P (Pic2P) for simulations of beam-cavity interactions dominated by space-charge effects. As opposed to standard space-charge dominated beam transport codes, which are based on the electrostatic approximation, Pic3P (Pic2P) includes space-charge, retardation and boundary effects as it self-consistently solves the complete set of Maxwell-Lorentz equations using higher-order finite element methods on conformal meshes. Use of efficient, large-scale parallel processing allows for the modeling of photoinjectors with unprecedented accuracy, aiding the design and operation of the next-generation of accelerator facilities. Applications to the Linac Coherent Light Source (LCLS) RF gun are presented.

• K. B. Buerkmann-Gehrlein
  
• T. Birke, J. Borninkhof, P. Budz, R. Daum, V. Duerr, J. Feikes, W. Gericke, H. G. Glass, H. G. Hoberg, J. Kolbe, R. Lange, G. Mielczarek, I. Mueller, K. Ott, J. Rahn, G. Schindhelm, T. Schneegans, Th. Schroeter, D. Schueler, D. Simmering, T. Westphal
  BESSY GmbH, Berlin
• R. Klein, G. Ulm
  PTB, Berlin

In 2003, the Metrology Light Source (MLS) was approved, a dedicated low energy electron storage ring of the Physikalisch-Technische-Bundesanstalt (PTB), the German national metrology institute. Design, construction and operation of the MLS are realized by BESSY, based on the PTB requirements for a permanent accessible radiometry source, optimized for the spectral range between UV up to VUV. The MLS is tunable in energy between 200 MeV and 600 MeV. Based on the experiences at BESSY, a highly stable and reliable Race Track Microtron for injection was realized by Danfysik. The commissioning of the 100 MeV microtron at the MLS started in December 2006. The concept and construction as well as the main parameters of the microtron are introduced.

• L. Froehlich
  

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

• S. Lederer
  
• G. Asova, J. W. Baehr, C. H. Boulware, H.-J. Grabosch, M. Hanel, S. Khodyachykh, S. A. Korepanov, M. Krasilnikov, B. Petrosyan, S. Rimjaem, T. A. Scholz, L. Staykov, F. Stephan
  DESY Zeuthen, Zeuthen
• K. Boyanov
  INRNE, Sofia
• L. H. Hakobyan
  YerPhI, Yerevan
• P. Michelato, L. Monaco, C. Pagani, D. Sertore
  INFN/LASA, Segrate (MI)
• R. Richter
  BESSY GmbH, Berlin
• J. Roensch
  Uni HH, Hamburg

Beginning 2007, a new gun cavity will be installed at the photo injector test facility at DESY in Zeuthen (PITZ). It will be conditioned towards gradients as high as 60 MV/m. This gradient is required for the operation of the European XFEL. Results from the conditioning for high peak power and high duty cycle will be reported.

• G. D'Auria
  
• D. Bacescu, L. Badano, F. Cianciosi, P. Craievich, M. B. Danailov, G. Penco, L. Rumiz, M. Trovo, A. Turchet
  ELETTRA, Basovizza, Trieste
• H. Badakov, A. Fukasawa, B. D. O'Shea, J. B. Rosenzweig
  UCLA, Los Angeles, California

• 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

• K. Togawa
  
• A. Higashiya, T. Shintake
  RIKEN Spring-8 Harima, Hyogo

• 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

• 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

• 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)

• A. P. Lee
  
• S.-S. Chang, J.-Y. Hwang, W. K. Lau, C. C. Liang, G.-H. Luo, T.-T. Yang
  NSRRC, Hsinchu

• T.-T. Yang
  
• C.-S. Fann, K. T. Hsu, S. Y. Hsu, J.-Y. Hwang, W. K. Lau, A. P. Lee, C. C. Liang, K.-K. Lin, K.-B. Liu, Y.-C. Liu, H. M. Shih, M.-S. Yeh
  NSRRC, Hsinchu

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

• 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

• V. D. Shiltsev
  

• 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.

• 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.

• C. K. Sinclair
  
• I. V. Bazarov, B. M. Dunham, Y. Li, X. G. Liu
  Cornell University, Department of Physics, Ithaca, New York
• K. W. Smolenski
  CLASSE, Ithaca

We have constructed a very high voltage photoemission electron gun as the electron source of a high brightness, high average current injector for an energy recovery linac (ERL) synchrotron radiation light source. The source is designed to deliver 100 mA average current in a CW 1300 MHz pulse train (77 pC/bunch). The cathode voltage may be as high as 750 kV. Negative electron affinity photocathodes are employed to obtain small thermal emittances. The electrode structure is assembled without touching any electrode surface. A load-lock system allows cleaning and activation of cathode samples prior to installation in the electron gun. Cathodes are cleaned by heating and exposure to atomic hydrogen, and activated with cesium and nitrogen trifluoride. Two cathode electrode sets, of 316LN stainless steel and Ti4V6Al alloy, have been used. The anode is beryllium. The internal surface of the ceramic insulator of the gun has a high resistivity fired coating, providing a path to drain away charge from field emission. Non-evaporable getters provide a very high pumping speed for hydrogen. Operating experience with this gun will be presented.

• 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.

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

• 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.

• D. Dowell
  
• E. N. Jongewaard, J. R. Lewandowski, Z. Li, C. Limborg-Deprey, J. F. Schmerge, A. E. Vlieks, J. W. Wang, L. Xiao
  SLAC, Menlo Park, California

The beam quality and operational requirements for the Linac Coherent Light Source (LCLS) currently being constructed at SLAC are exceptional, requiring the design of a new RF photocathode gun for the electron source. Based on operational experience at GTF at SLAC, SDL and ATF at BNL and other laboratories, the 1.6cell s-band (2856MHz) gun was chosen to be the best electron source for the LCLS injector, however a significant re-design was necessary to achieve the challenging parameters. Detailed 3-D analysis and design was used to produce nearly-perfect rotationally symmetric rf fields to achieve the emittance requirement. In addition, the thermo-mechanical design allows the gun to operate at 120Hz and a 140MV/m cathode field, or to an average power dissipation of 4kW. Both average and pulsed heating issues are addressed in the LCLS gun design. The first LCLS gun is now fabricated and has been operated with high-power RF. The results and analysis of these high-power tests will be presented.

• D. Dowell
  
• E. N. Jongewaard, C. Limborg-Deprey, J. F. Schmerge, A. E. Vlieks
  SLAC, Menlo Park, California

The field emission was measured during the high-power testing of the LCLS photocathode RF gun. A careful study and analysis of the field emission electrons, or dark current is important in assessing the gun's internal surface quality in actual operation, especially those surfaces with high fields. The charge per 2 microsecond long RF pulse (the dark charge) was measured as a function of the peak cathode field for the 1.6 cell, 2.856GHz LCLS RF gun. Faraday cup data was taken for cathode peak RF fields up to 120MV/m producing a maximum of 0.6nC/RF pulse for a diamond-turned polycrystalline copper cathode installed in the gun. The field dependence of the dark charge is analyzed using a temperature-dependent Fowler-Nordheim (FN) theory to obtain the field enhancement factor and other emitter parameters. Digitized images of the dark charge were taken using a 100 micron thick YAG crystal for a range of solenoid fields to determine the location and angular distribution of the field emitters. The FN plots and emitter image analysis will be described in this paper.

• 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.

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

• P. Evtushenko
  
• S. V. Benson, D. Douglas, G. Neil
  Jefferson Lab, Newport News, Virginia

• A. S. Hofler
  
• P. Evtushenko
  Jefferson Lab, Newport News, Virginia
• M. Krasilnikov
  DESY Zeuthen, Zeuthen

Injector gun design is an iterative process where the designer optimizes a few nonlinearly interdependent beam parameters to achieve the required beam quality for a particle accelerator. Few tools exist to automate the optimization process and thoroughly explore the parameter space. The challenging beam requirements of new accelerator applications such as light sources and electron cooling devices drive the development of RF and SRF photo injectors. RF and SRF gun design is further complicated because the bunches are space charge dominated and require additional emittance compensation. A genetic algorithm has been successfully used to optimize DC photo injector designs for Cornell* and Jefferson Lab**, and we propose studying how the genetic algorithm techniques can be applied to the design of RF and SRF gun injectors. In this paper, we report on the initial phase of the study where we model and optimize gun designs that have been benchmarked with beam measurements and simulation.

* I. Bazarov, et al., "Multivariate Optimization of a High Brightness DC Gun Photoinjector", PRST-AB 2005.** F. Hannon, et al., "Simulation and Optimisation of a 100 mA DC Photoinjector", EPAC 2006.

• V. Litvinenko
  
• J. Alduino, D. Beavis, I. Ben-Zvi, M. Blaskiewicz, J. M. Brennan, A. Burrill, R. Calaga, P. Cameron, X. Chang, K. A. Drees, G. Ganetis, D. M. Gassner, J. G. Grimes, H. Hahn, L. R. Hammons, A. Hershcovitch, H.-C. Hseuh, A. K. Jain, D. Kayran, J. Kewisch, R. F. Lambiase, D. L. Lederle, C. Longo, G. J. Mahler, G. T. McIntyre, W. Meng, T. C. Nehring, B. Oerter, C. Pai, D. Pate, D. Phillips, E. Pozdeyev, T. Rao, J. Reich, T. Roser, T. Russo, Z. Segalov, J. Smedley, K. Smith, J. E. Tuozzolo, G. Wang, D. Weiss, N. Williams, Q. Wu, K. Yip, A. Zaltsman
  BNL, Upton, Long Island, New York
• H. Bluem, M. D. Cole, A. J. Favale, D. Holmes, J. Rathke, T. Schultheiss, A. M.M. Todd
  AES, Princeton, New Jersey
• B. W. Buckley
  CLASSE, Ithaca
• G. Citver
  Stony Brook University, StonyBrook
• J. R. Delayen, L. W. Funk, H. L. Phillips, J. P. Preble
  Jefferson Lab, Newport News, Virginia

In this paper we present status and plans for the 20-MeV R&D energy recovery linac, which is under construction at Collider Accelerator Department at BNL. The facility is based on high current (up to 0.5 A of average current) super-conducting 2.5 MeV RF gun, single-mode super-conducting 5-cell RF linac and about 20-m long return loop with very flexible lattice. The R&D ERL, which is planned for commissioning in 2008, aims to address many outstanding questions relevant for high current, high brightness energy-recovery linacs.

• 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.

• V. Kamerdzhiev
  
• R. J. Hively, G. F. Kuznetsov, H. Pfeffer, G. W. Saewert, V. D. Shiltsev, X. Zhang
  Fermilab, Batavia, Illinois

• M. E. Conde
  

There has been continued interest in the development of dielectric-loaded wakefield structures that can be used to accelerate particle beams. The present search for materials able to withstand very intense RF fields has renewed this interest. Recent experiments at the Argonne Wakefield Accelerator have generated short RF pulses with accelerating fields in excess of 80 MV/m. These experiments used ceramic-lined cylindrical waveguides, operating at frequencies between 10 and 15 GHz. Other important experiments, at different RF frequencies and using planar or cylindrical geometries, have been carried out at various other facilities. A number of new experiments are planned in the near future to explore the capabilities of this class of structures. This presentation will provide an up-to-date survey of the activities in this area of research.

• I. Ben-Zvi
  
• D. T. Abell, G. I. Bell, D. L. Bruhwiler, R. Busby, J. R. Cary, D. A. Dimitrov, P. Messmer, V. H. Ranjbar, D. S. Smithe, A. V. Sobol, P. Stoltz
  Tech-X, Boulder, Colorado
• J. Alduino, D. S. Barton, D. Beavis, M. Blaskiewicz, J. M. Brennan, A. Burrill, R. Calaga, P. Cameron, X. Chang, K. A. Drees, A. V. Fedotov, W. Fischer, G. Ganetis, D. M. Gassner, J. G. Grimes, H. Hahn, L. R. Hammons, A. Hershcovitch, H.-C. Hseuh, D. Kayran, J. Kewisch, R. F. Lambiase, D. L. Lederle, V. Litvinenko, C. Longo, W. W. MacKay, G. J. Mahler, G. T. McIntyre, W. Meng, B. Oerter, C. Pai, G. Parzen, D. Pate, D. Phillips, S. R. Plate, E. Pozdeyev, T. Rao, J. Reich, T. Roser, A. G. Ruggiero, T. Russo, C. Schultheiss, Z. Segalov, J. Smedley, K. Smith, T. Tallerico, S. Tepikian, R. Than, R. J. Todd, D. Trbojevic, J. E. Tuozzolo, P. Wanderer, G. Wang, D. Weiss, Q. Wu, K. Yip, A. Zaltsman
  BNL, Upton, Long Island, New York
• A. V. Aleksandrov, D. L. Douglas, Y. W. Kang
  ORNL, Oak Ridge, Tennessee
• H. Bluem, M. D. Cole, A. J. Favale, D. Holmes, J. Rathke, T. Schultheiss, J. J. Sredniawski, A. M.M. Todd
  AES, Princeton, New Jersey
• A. V. Burov, S. Nagaitsev, L. R. Prost
  Fermilab, Batavia, Illinois
• Y. S. Derbenev, P. Kneisel, J. Mammosser, H. L. Phillips, J. P. Preble, C. E. Reece, R. A. Rimmer, J. Saunders, M. Stirbet, H. Wang
  Jefferson Lab, Newport News, Virginia
• V. V. Parkhomchuk, V. B. Reva
  BINP SB RAS, Novosibirsk
• A. O. Sidorin, A. V. Smirnov
  JINR, Dubna, Moscow Region

The physics interest in a luminosity upgrade of RHIC requires the development of a cooling-frontier facility. Detailed cooling calculations have been made to determine the efficacy of electron cooling of the stored RHIC beams. This has been followed by beam dynamics simulations to establish the feasibility of creating the necessary electron beam. Electron cooling of RHIC at collisions requires electron beam energy up to about 54 MeV at an average current of between 50 to 100 mA and a particularly bright electron beam. The accelerator chosen to generate this electron beam is a superconducting Energy Recovery Linac (ERL) with a superconducting RF gun with a laser-photocathode. An intensive experimental R&D program engages the various elements of the accelerator: Photocathodes of novel design, superconducting RF electron gun of a particularly high current and low emittance, a very high-current ERL cavity and a demonstration ERL using these components.

• E. Vogel
  
• C. Gerth, W. Koprek, F. Loehl, D. Noelle, H. Schlarb, T. Traber
  DESY, Hamburg

At pulsed linear accelerators, fast proportional rf control compensates beam loading sufficiently for single or a few bunches. In the case of long bunch trains, additional measures have to be taken commonly by adding a compensation signal to the rf drive signals calculated from the predicted beam intensity. In contrast to predictive methods, techniques based on real time beam measurements are sensitive to fast changes of the beam intensity and bunch patterns. At FLASH we apply a beam loading compensation scheme based on toroid monitor signals. This paper presents the compensation scheme, the calibration procedure and the effect on the beam.

• V. Vogel
  
• A. Cherepenko
  BINP SB RAS, Novosibirsk
• S. Choroba, T. Froelich, T. G. Grevsmuehl, F.-R. Kaiser, V. V. Katalev, I. S. Sokolov, H. Timm
  DESY, Hamburg

• Y. H. Chin
  
• K. Hayashi
  TETD, Otawara
• M. Y. Miyake, Y. Yano
  Toshiba, Yokohama

• B. H. Chung
  
• K.-H. Chung
  KAPRA, Cheorwon
• J. S. Hong, J. H. Jeon, S. J. Noh
  Dankook University, Seoul
• S. K. Ko
  University of Ulsan, Ulsan

• V. Kamerdzhiev
  
• H. Pfeffer, G. W. Saewert, V. D. Shiltsev, D. Wolff
  Fermilab, Batavia, Illinois

• S. P. Virostek
  
• M. D. Hoff, D. Li, J. W. Staples, R. P. Wells
  LBNL, Berkeley, California

A high-yield neutron source to screen sea-land cargo containers for shielded Special Nuclear Materials (SNM) has been designed at LBNL. The Accelerator-Driven Neutron Source (ADNS) utilizes the D(d,n)³He reaction to produce a forward directed neutron beam. Key components are a high-current radio-frequency quadrupole (RFQ) accelerator and a high-power neutron production target capable of delivering a neutron flux of >10⁷ n/(cm² s) at a distance of 2.5 m. The mechanical design and analysis of the four-module, bolt-together RFQ will be presented here. Operating at 200 MHz, the 5.1 m long RFQ will accelerate a 40 mA deuteron beam to 6 MeV. At a 5% duty factor, the time-average d+ beam current on target is 1.5 mA. Each of the 1.27 m long RFQ modules will consist of four solid OFHC copper vanes. A specially designed 3-D O-ring will be used to provide vacuum sealing between both the vanes and the modules. RF connections are made by means of canted coil spring contacts. Quadrupole mode stabilization is obtained with a series of 60 water-cooled pi-mode rods. A set of 80 evenly spaced fixed slug tuners is used for final frequency adjustment and local field perturbation correction.

• S. A. Belomestnykh
  
• V. D. Shemelin, K. W. Smolenski, V. Veshcherevich
  CLASSE, Ithaca

A 1300 MHz deflecting cavity will be used for beam slice emittance measurements, and to study the temporal response of negative electron affinity photocathodes in the ERL injector currently under construction at Cornell University. A single-cell TM110-mode cavity was designed to deflect the beam vertically. The paper describes the cavity shape optimization procedure, its mechanical design and performance at low RF power.

• R. L. Geng
  
• P. Barnes, B. Clasby, J. Kaminski, M. Liepe, V. Medjidzade, D. Meidlinger, H. Padamsee, J. Sears, V. D. Shemelin, N. Sherwood, M. Tigner
  CLASSE, Ithaca

Six 1300 MHz superconducting niobium 2-cell cavities are manufactured for the prototype of Cornell ERL injector to boost the energy of a high current, low emittance beam produced by a DC gun. Designed for high current beam acceleration, these cavities have new characteristics as compared to previously developed low-current cavities such as those for TTF. Precision manufacture is emphasized for a better straightness of the cavity axis so as to avoid unwanted emittance dilution. We present the manufacturing, processing and vertical test performance of these cavities. We also present the impact of new cavity characteristics to the cavity performance as learnt from vertical tests. Solutions for improving cavity performance are discussed.

• A. M. Cook
  
• M. P. Dunning, J. B. Rosenzweig, K. M. Serratto
  UCLA, Los Angeles, California
• P. Frigola
  RadiaBeam, Los Angeles, California

The pi-mode resonant frequency of the 1.6 cell SLAC/BNL/UCLA style RF photoinjector electron gun is conventionally tuned using cylindrical copper tuning pieces that extend into the full-cell cavity through holes in the side of the gun. This design begins to fail in many versions of this popular gun design at higher voltage levels, when the cavity undergoes electric breakdown in the vicinity of the tuners. In order to remove the tuners from the region of high electric field, mitigating this problem, the full cell geometry must be changed significantly. We report on a method of accomplishing this, in which we use a mechanical device of custom design to stretch the cavity structure of an existing photoinjector in order to tune the resonant frequency up by over 2 MHz. We present results of testing the modified photoinjector in an RF test bed with both copper and magnesium cathodes, succeeding in putting approximately 8 - 10 MW of RF power into the gun. This is an improvement over the 4 MW routinely achieved in a similar gun using conventional tuning methods installed at the UCLA Neptune laboratory.

• B. D. O'Shea
  
• D. Alesini, M. Ferrario, B. Spataro
  INFN/LNF, Frascati (Roma)
• A. Boni, A. Fukasawa, J. B. Rosenzweig
  UCLA, Los Angeles, California
• L. Ficcadenti, A. Mostacci, L. Palumbo
  Rome University La Sapienza, Roma

The hybrid photoinjector is a high current, low emittance photoinjector/accelerator and is under design and collaboration at Roma University La Sapienza, INFN - Laboratori Nazionali di Frascati and the UCLA Particle Beam Physics Lab. The hybrid standing wave-traveling wave photoinjector uses a coupling cell to divide power between a high-field 1.6 cell standing wave photoinjector, for electron emission and collection, and a low power traveling wave accelerator, for acceleration to desired energies at low emittances. Simulation results show promising beam properties of less than 4 mm-mrad emittance, energy spreads of 1.5%, and currents as high as 1.2 kA at energies of 21 MeV. We report on the progress of RF design and results of cold test RF measurements at the UCLA Pegasus Laboratory, including methods for measurements and difficulties arising in the transition from simulation to physical measurements.

• V. A. Dolgashev
  
• M. Borland, G. J. Waldschmidt
  ANL, Argonne, Illinois

• J. L. Hirshfield, J. L. Hirshfield, E. V. Kozyrev, M. A. LaPointe
  Yale University, Physics Department, New Haven, CT
• S. V. Shchelkunov
  Columbia University, New York
• M. Y. Shmelyov
  IAP/RAS, Nizhny Novgorod
• V. P. Yakovlev
  Omega-P, Inc., New Haven, Connecticut

Development of a future multi-TeV warm collider demands new technological solutions and new accelerator structure materials. The Ka-Band test facility being put into operation at Yale University that centers on the Yale/Omega-P 34-GHz magnicon allows users to carry out high gradient experiments on RF breakdown, pulse fatigue, tests of new high power pulse manipulation systems, and RF components. The magnicon is now conditioned for a pulse width up to 1 μs, at an output power level high enough for basic studies of electric and magnetic RF field limits at surfaces of conductors and dielectrics. The high-power waveguide transmission system for the facility is assembled and ready for tests. It includes RF windows, phase shifters, 13 mm diameter TE 11 waveguides, mode converters, etc. Recently the assembled system has undergone conditioning in preparation for carrying out first "user" experiments.

• V. P. Yakovlev
  
• J. L. Hirshfield
  Omega-P, Inc., New Haven, Connecticut
• S. Kazakov
  KEK, Ibaraki

A relatively simple and inexpensive two-cavity 45 MW, 22.8 GHz second-harmonic multiplier is considered as an RF source for High-Gradient experiments. The design is to be based on use of an existing SLAC electron gun, such as the XL-4 gun. RF drive power would be supplied from a 50 MW SLAC klystron and modulator, and a second modulator would be used to power the gun in the multiplier. An important feature of the harmonic multiplier is TE 01 circular waveguide for output RF power extraction.

• N. Barov
  

FAR-TECH, Inc. is developing and building a 36 kV, 830 kW klystron for the International Linear Collider (ILC) testing program. A variant of the tube can also be used to supply RF energy for a 2-3 meter section of ILC. The tube design is of the multiple-beam klystron (MBK) type, using ten beams with confined flow focusing. The design optimizes small tube size and low cost. The initial prototype will use an electromagnet, but the design allows for the eventual use of a permanent magnet solenoid. An efficiency of 65% is expected. We will present the design and status of the construction of the klystron and supporting systems.

• A. Burrill
  
• I. Ben-Zvi
  BNL, Upton, Long Island, New York
• M. D. Cole, J. Rathke
  AES, Princeton, New Jersey
• P. Kneisel, R. Manus, R. A. Rimmer
  Jefferson Lab, Newport News, Virginia

The multipacting phenomena in accelerating structures and coaxial lines are well documented and methods of mitigating or suppressing it are understood. The multipacting that occurs in a quarter wave choke joint designed to mount a cathode insertion stalk into a superconducting RF photoinjector has been analyzed via calculations and experimental measurements and the effect of introducing multipacting suppression grooves into the structure is analyzed. Several alternative choke joint designs are analyzed and suggestions made regarding future choke joint development. Furthermore, the problems encountered in cleaning the choke joint surfaces, factors important in changes to the secondary electron yield, are discussed and evaluated. This design is being implemented on the BNL 1.3 GHz photoinjector, previously used for measurement of the quantum efficiency of bare Nb, to allow for the introduction of other cathode materials for study, and to verify the design functions properly prior to constructing our 703 MHz photoinjector with a similar choke joint design.

• X. Chang
  
• I. Ben-Zvi, J. Kewisch, C. Pai
  BNL, Upton, Long Island, New York

• C. Wilsen
  
• M. F. Kirshner, R. D. Kowalczyk
  L-3, Williamsport, Pennsylvania

* M. F. Kirshner et al., "Apparatus and method for trajectory modulation of an electron beam," U. S. Provisional Patent Application 60/838,580, August 17, 2006. Cleared by DoD/OFOISR for public release under 07-S-0493 on January 22, 2007

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

• D. Sertore
  
• P. Michelato, L. Monaco, C. Pagani
  INFN/LASA, Segrate (MI)

Based on our experience on photocathode production, we present in this paper the results of the application of different optical diagnostic techniques on fresh and used photocathodes. These techniques allow to study effects like non uniformity, cathode aging, etc. In particular, photocathode optical parameters and QE characterization, both done at different wavelengths, give fundamentals information for the construction of a model of the photoemission process to be applied to Cs2Te photocathodes. These studies are useful for further improving key cathode features, such as its robustness and lifetime as well as to study and control the photocathodes thermal emittance.

• 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.

• T. Sugimura
  
• M. Ikeda, S. Ohsawa
  KEK, Ibaraki

• T. Natsui
  
• M. Akemoto, S. Fukuda, T. Higo, N. Kudoh, T. T. Takatomi, M. Yoshida
  KEK, Ibaraki
• K. Dobashi, M. Uesaka, T. Yamamoto
  UTNL, Ibaraki
• F. Sakamoto, A. Sakumi
  The University of Tokyo, Nuclear Professional School, Ibaraki-ken
• E. Tanabe
  AET Japan, Inc., Kawasaki-City

• 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

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

* J. Yang, T. Kondoh, K. Kan, T. Kozawa, Y. Yoshida and S. Tagawa: Nucl. Instrum. Methods Phys. Res., Sect. A 556 (2006) 52-56

• 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

• 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.

• M. Church
  
• S. Nagaitsev, P. Piot
  Fermilab, Batavia, Illinois

• J. W. Staples
  
• K. M. Baptiste, J. N. Corlett, S. Kwiatkowski, S. M. Lidia, J. Qiang, F. Sannibale, K. G. Sonnad, S. P. Virostek, R. P. Wells
  LBNL, Berkeley, California

New generation accelerator-based X-ray light sources require high quality beams with high average brightness. Normal conducting L- and S-band photoinjectors are limited in repetition rate and D-C (photo)injectors are limited in field strength at the cathode. We propose a low frequency normal-conducting cavity, operating at 50 to 100 MHz CW, to provide beam bunches at a rate of one MegaHertz or more. The photoinjector uses a re-entrant cavity structure, requiring less than 100 kW CW, with a peak wall power density less than 10 W/cm². The cavity will support a vacuum down to 10 picoTorr, with a load-lock mechanism for easy replacement of photocathodes. The photocathode can be embedded in a magnetic field to provide correlations useful for flat beam generation. Beam dynamics simulations indicate that normalized emittances on the order of 1 mm-mrad are possible with gap voltage of 750 kV, with fields up to 20 MV/m at the photocathode, for 1 nanocoulomb charge per bunch after acceleration and emittance compensation. Long-bunch operation (10's of picosecond) is made possible by the low cavity frequency, permitting low bunch current at the 750 kV gap voltage.

• 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.

• F. Zhou
  
• Y. K. Batygin, A. Brachmann, J. E. Clendenin, R. H. Miller, J. Sheppard, M. Woodley
  SLAC, Menlo Park, California

A train of 2-nsμbunches are generated in the DC-gun based injector in the ILC e^- source; a bunching system with extremely high bunching efficiency to compress bunch down to 20 ps FWHM is designed. Complete optics to transport the electron beam to the 5-GeV damping ring injection line is developed. Start-to-end multi-particle tracking through the beamline is performed including the bunching system, pre-acceleration, chicane, 5-GeV SC booster linac, spin rotators and energy compressor. It shows more than 95% of electrons from the DC-gun are captured within the 6-D damping ring acceptance at the entrance of damping ring injection line. The field and alignment errors, and orbit correction are analyzed.

• 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).

• H. Bluem
  

High power RF testing has been performed on a novel axisymmetric radiofrequency electron gun at a frequency of 11.43 GHz using the magnicon facility at the Naval Research Laboratory. This gun utilizes coaxial coupling from the upstream end of unit and allows for axisymmetric tuning of both the cathode cell and the second cell. The features of the gun have been proven to operate at high gradients. The overall design of the gun will be discussed along with the results of the high power RF testing.

• 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.

• J. Kewisch
  
• X. Chang
  BNL, Upton, Long Island, New York

Emittance compensation is a well established technique* for minimizing the emittance of electron beam from a RF photo-cathode gun. Longitudinal slices of a bunch have a small emittance, but due to the longitudinal charge distribution of the bunch and time dependent RF fields they are not focused in the same way, so that the direction of their phase ellipses diverges in phase space and the projected emittance is much larger. Emittance compensation reverses the divergence. At the location where the slopes of the phase ellipses coincides the beam is accelerated, so that the space charge forces are reduced. A recipe for emittance compensation is given in reference**. For magnetized beams (where the angular momentum is non-zero) such emittance compensation is not sufficient because variations in the slice radius lead to variations in the angular speed and therefore to an increase of emittance in the rotating frame. We describe a method and tools for a compensation that includes the beam magnetization.

* L. Serafini, J. B. Rosenzweig, Phys. Rev E 55, 7565, (1997)
** X. Y. Chang, I. Ben-Zvi, J. Kewisch, Phys. Rev ST AB 9, 044201, (2006)

• A. S. Setty
  

[1] D. Einfeld, "Status of the ALBA project", EPAC 06, Scotland, Edinburgh, June 2006.[2] D. Tronc and A. Setty, "Electrons RF auto-focusing and capture in bunchers", Linear Accelerator Conference 1988, Virginia.

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

• B. Sayyar-Rodsari
  
• E. Hartman, C. A. Schweiger
  Pavilion Technologies, Inc, Austin, Texas
• M. J. Lee, P. Lui, J. M. Paterson, J. F. Schmerge
  SLAC, Menlo Park, California

High brightness electron beam sources such as rf photo-injectors as proposed for SASE FELs must consistently produce the desired beam quality. We report the results of a study in which a combined neural network (NN) and first-principles (FP) model is used to model the transverse phase space of the beam as a function of quadrupole magnet current, while beam charge, solenoid field, accelerator gradient, and linac voltage and phase are kept constant. The parametric transport matrix between the exit of the linac section and the spectrometer screen constitutes the FP component of the combined model. The NN block provides the parameters of the transport matrix as functions of quad current. Using real data from SLAC Gun Test Facility, we will highlight the significance of the constrained training of the NN block and show that the phase space of the beam is accurately modelled by the combined NN and FP model, while variations of beam matrix parameters with the quad current are correctly captured. We plan to extend the combined model in the future to capture the effects of variations in beam charge, solenoid field, and accelerator voltage and phase.

• C. P. Neuman
  
• P. G. O'Shea
  UMD, College Park, Maryland

(*) Simulation of Longitudinally Modulated Electron Beams. C. P. Neuman and P. G. O'Shea. In 2006 Advanced Accelerator Concepts Workshop, AIP Conference Proceedings, 877, 621-627. Melville, AIP (2006).

• C. P. Neuman
  
• P. G. O'Shea
  UMD, College Park, Maryland

(*) Simulation of Longitudinally Modulated Electron Beams. C. P. Neuman and P. G. O'Shea. In 2006 Advanced Accelerator Concepts Workshop, AIP Conference Proceedings 877, edited by M. Conde and C. Eyberger, 621-627. Melville, NY, AIP (2006).

• I. Haber
  
• S. Bernal, R. Feldman, R. A. Kishek, P. G. O'Shea, C. Papadopoulos, M. Reiser, D. Stratakis, M. Walter
  UMD, College Park, Maryland
• A. Friedman, D. P. Grote
  LLNL, Livermore, California
• J.-L. Vay
  LBNL, Berkeley, California

One of the areas fundamental beam physics that serve as the rationale for recent research on UMER is the study of generation and evolution of beam halos. This physics can be accessed on a scaled basis in UMER at a small fraction of the cost of similar experiments on a much larger machine. Recent experiments and simulations have identified imperfections in the source geometry, particularly in the region near the emitter edge, as a potentially significant source of halo particles. The edge-generated halo particles, both in the experiments and the simulations are found to pass through the center of the beam in the vicinity of the anode plane. Understanding the detailed evolution of these particle orbits is therefore important to designing any aperture to remove the beam halo. Both experimental data and simulations will be presented to illustrate the details of this mechanism for halo formation.

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

Longitudinal perturbations can be generated in the space-charge dominated regimes in which most beams of interest are born. To study the modification of transverse beam distributions by longitudinal beam dynamics, we have conducted experimental studies using low energy electron beams by taking time resolved images of a beam with longitudinal density perturbations. Two different diagnostics are used: optical transition radiation (OTR) produced from an intercepting silicon based aluminum screen and a fast (<5ns decay time) phosphor screen. It is found that the beam is significantly affected by the perturbation. However the OTR signal is very weak and requires over 45 minutes of frame integration. The fast phosphor screen has much better sensitivity (~1'000 times enhancement). In this paper, we also report on the time resolved measurement of a parabolic beam, showing interesting correlations between transverse and longitudinal distributions of the beam.

• J. F. DeFord
  
• B. Held
  STAR, Inc., Mequon, Wisconsin
• J. J. Petillo
  SAIC, Burlington, Massachusetts

Particle orbit errors in multipacting and dark current computations can arise from inadequate field representation, poor surface modeling, and from the integration algorithm used to advance the particles. Established fields-based adaptive mesh refinement (AMR) methods *,** selectively improve the field and surface representation over several iterations in finite-element codes but they are not optimized for particle tracking. In particular, field emission and secondary emission models require precise surface representations and highly accurate field representations near surfaces, and these requirements are not adequately addressed in standard AMR techniques. In this paper we report on extensions to existing AMR support in the Analyst software package for particle tracking, including adaptive improvement of near-surface and on-surface field representations, and control of element aspect ratios throughout successive iterations. We also discuss the merits of automated identification of important regions of the mesh based on field levels and orbit estimation to guide AMR in multipacting calculations, and multipacting results for a SRF cavity will be presented.

* G. Drago, et al., IEEE Trans. on Mag., 28, 1992, pp. 1743-1746.** D. K. Sun, et al., IEEE Trans. on Mag., 36, July 2000, pp. 1596-1599.

• A. Fukasawa
  
• D. Alesini, M. Ferrario, B. Spataro
  INFN/LNF, Frascati (Roma)
• A. Boni, B. D. O'Shea, J. B. Rosenzweig
  UCLA, Los Angeles, California
• L. Ficcadenti, A. Mostacci, L. Palumbo
  Rome University La Sapienza, Roma

• A. Krasnykh
  

A novel 3D method of sheet beam (SB) gun design has recently been developed. Second order ruled surfaces (SORS) to define the geometry of the gun electrodes. The gun design process is made simpler if SORS are derived from simple analytical formulas. The coefficients of the mathematical expression are parameters that set the gun optic. A proposed design method is discussed and illustrated.

• A. Krasnykh
  

A classical electron/positron accelerating structure is a disk loaded cylindrical waveguide. The accelerator structure here has azimuth symmetry. The proposed structure contains a disk-loaded cylindrical waveguide where there is a periodical change of rf-field vs. azimuth. The modulation deforms the rf-field in such a manner that the accelerated particles undergo transverse focusing forces. The new class of accelerator structures covers the initial part of e⁺/e^- linacs where a bunch is not rigid and additional transverse focusing fields are necessary. We discuss a bunch formation with a high transverse aspect ratio in the proposed structure and particularly in the photoinjector part of a linac.

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

One of the most important targets for building modern particle accelerators is to increase the beam brightness. The purposes of building a dc/rf gun are to seek high bunch charge and low beam transverse emittance, two key parameters for enhancing brightness of accelerators. We present simulation results of the beam emittance changes in a dc/rf gun under different gun voltages. SUPERFISH and PARMELA were used to simulate the beam dynamics in the gun. These simulations indicate that a small beam transverse emittance (< 0.5 mm.mrad) can be obtained when the voltage on the dc gap is lower than 200 kV and the bunch charge is 200 pc, and increments of dc gap voltages will greatly improve the emittances.

• D. Kayran
  
• I. Ben-Zvi, R. Calaga, X. Chang, J. Kewisch, V. Litvinenko, E. Pozdeyev
  BNL, Upton, Long Island, New York

Non-magnetized electron cooling of RHIC requires an electron beam energy of 54.3 MeV, electron charge per bunch of 5 nC, normalized rms beam emittance of 4 mm-mrad, and rms energy spread of 3·10^-4 *. In this paper we describe a lattice of a two-pass SCRF energy recovery linac (ERL) and results of a PARMELA simulation that provides electron beam parameters satisfying RHIC electron cooling requirements.

* A. Fedotov, Electron Cooling Studies for RHIC II http://www.bnl.gov/cad/ecooling/docs/PDF/Electron_Cooling.pdf

• D. Kayran
  
• V. Litvinenko
  BNL, Upton, Long Island, New York

A super-conducting RF R&D Energy recovery linac (ERL) is under construction at Brookhaven National Laboratory (BNL). This ERL will be used as a test facility to study issues relevant to high-current, high-brightness beams. One of the goals is to demonstrate an electron beam with high charge per bunch (~ 5 nC) and extremely low normalized emittance (~ 5 mm-mrad) at an energy of 20 MeV. In contrast with operational high-brightness linear electron accelerators, all presently operating ERLs have an order of magnitude larger emittances for the same charge per bunch. One reason for this emittance growth is that the merger system mixes transverse and longitudinal degrees of freedom, and consequently violates emittance compensation conditions. A merger system based on zigzag scheme* resolves this problem. In this paper we discuss performance of the present design of the BNL R&D ERL injector with a zigzag merger.

* V. N. Litvinenko, R. Hajima, and D. Kayran, Nucl. Instr. and Meth. A 557 (2006) 165.

• 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

• C. Adolphsen
  

The ILC Linac Group at SLAC is actively pursuing a broad range of R&D to improve the reliability and reduce the cost of the L-band (1.3 GHz) rf system and normal-conducting accelerators. Current activities include the development of a Marx-style modulator and a 10 MW sheet-beam klystron, operation of an L-band (1.3 GHz) rf source using an SNS HVCM modulator and commercial klystron, construction of an rf distribution system with adjustable power tap-offs and custom hybrids, tests of cavity coupler components to understand rf processing limitations, simulation of multipacting in the couplers, optimization of the cavity fill parameters for operation with a large spread in sustainable cavity gradients and operation of a 5-cell prototype positron capture cavity. This paper surveys the results from the past year and reviews L-band R&D at other labs, in particular, that at DESY for the XFEL project.

• E. Arevalo
  
• W. Ackermann, R. Hampel, W. F.O. Muller, T. Weiland
  TEMF, Darmstadt

The computation of wake fields excited by ultra short electron bunches in accelerator components with geometrical discontinuities is a challenging problem, as an accurate resolution for both the small bunch and the large model geometry are needed. Several computational codes (PBCI, ROCOCO, CST PARTICLE STUDIO etc.) have been developed to deal with this type of problems. Wake field simulations of the RF electron gun of the Photoinjector Test Facility at DESY Zeuthen (PITZ) are performed whith different specialized codes. Here we present a comparison of the wake potentials calculated numerically obtained from the different codes. Several structures of the photoinjector are considered.

• Q. Luo
  
• H. He, P. Li, P. Lu, B. Sun, J. H. Wang
  USTC/NSRL, Hefei, Anhui

For the development of accelerators we require increasingly precise control of beam position. Cavity BPMs promise a much higher position resolution compared to other BPM types and manufacture of cavity BPMs is in general less complicated. The cavity BPM operating at S-band for HLS (Hefei Light Source) was designed. It consists of two cavities: a position cavity tuned to TM110 mode and a reference cavity tuned to TM010 mode. To suppress the monopole modes we use waveguides as pickups. Superheterodyne receivers are used in electronics for many cavity BPMs while we decide to use chip AD8302 produced by Analog Devices to process the signals. To simulate and calculate the electromagnetic field we use MAFIA.

• V. Volkov
  
• K. Floettmann
  DESY, Hamburg
• D. Janssen
  FZD, Dresden

• 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

• 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.

• E. Pozdeyev
  
• I. Ben-Zvi, P. Cameron, K. A. Drees, D. M. Gassner, D. Kayran, V. Litvinenko, G. J. Mahler, T. Rao
  BNL, Upton, Long Island, New York

The ERL Prototype project is currently under development at the Brookhaven National Laboratory. The ERL is expected to demonstrate energy recovery of high-intensity beams with a current of up to a few hundred milliamps, while preserving the emittance of bunches with a charge of a few nanocoulombs produced by a high-current SRF gun. To successfully accomplish this task the machine will include beam diagnostics that will be used for accurate characterization of the three dimensional beam phase space at the injection and recirculation energies, transverse and longitudinal beam matching, orbit alignment, beam current measurement, and machine protection. This paper outlines requirements on the ERL diagnostics and describes its setup and modes of operation.