03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques

T02 Lepton Sources

Paper Title Page
MOZBKI03 The JLab 12 GeV Energy Upgrade of CEBAF for QCD and Hadronic Physics 58
 
  • L. S. Cardman, L. Harwood
    Jefferson Lab, Newport News, Virginia
  
  Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177

CEBAF is a 5-pass, recirculating cw electron linac operating at ~6 GeV. The 12-GeV Upgrade is a $300M project anticipated to receive Critical Decision 2 approval in late summer of 2007 and begin construction activities in 2008; funding for the project is provided by the DOE Office of Nuclear Physics which will double the beam energy. The new energy reach will permit significant extensions in research into non-perturbative aspects of QCD. Areas of interest are Generalized Parton Distributions (GPDs), measurements at high-xBjorken, and the use of hybrid mesons to explore the nature of quark confinement. The upgrade includes: doubling the accelerating voltages of the linacs by adding 10 new high-performance cryomodules plus the requisite expansion of the 2K cryogenics plant and rf power systems, upgrading the beam transport system from 6 GeV to 12 GeV capability through extensive re-use of existing hardware, adding one recirculation arc, adding a new experimental area and the beamline to it, building new experimental equipment for the GPD, high-xBjorken, and hybrid mesons programs. The presentation will touch on the science and give some details of the accelerator plans.

 
slides icon Slides  
THPMN003 Commissioning of the 100 keV Beam Stage of the Injector Linac of the IFUSP Microtron 2710
 
  • M. N. Martins, A. L. Bonini, R. Lima, A. A. Malafronte, T. F. Silva
    USP/LAL, Sao Paulo
  
  Funding: Work supported by FAPESP and CNPq

The injector linac consists of a beam conforming stage, with chopper and buncher systems, and two acceleration structures, the first one with variable β, and the second one divided into two parts with different β. There are two 3-mm diameter collimators, the first at the entrance to the first chopper cavity and the second at the entrance to the first acceleration structure. The beam focalization is made by solenoids, and correcting coils are provided for steering. In this work we describe the commissioning of the optical lattice of the conforming beam stage. The first beam images are shown.

 
THPMN017 Polarized Positron Production and Tracking at the ILC Positron Source 2742
 
  • A. Ushakov, S. Riemann, A. Schaelicke
    DESY Zeuthen, Zeuthen
  
  Funding: This work is supported by the Commission of the European Communities under the 6th Framework Programme "Structuring the European Research Area", contract number RIDS-011899.

A positron source based on a helical undulator system is planned to be used for the future International Linear Collider (ILC). Depending on the accelerator design it will be possible to get polarized positrons at the interaction point. A source performance with high positron yield and high polarization is the aim of our design studies. We focus on the optimization of target and capture section using several simulation codes. FLUKA is a suitable tool to calculate the positron yield, heat deposition, neutron generation and induced activity of source parts. The ASTRA code is used to calculate positron capture efficiency into the optical matching device. The new release of Geant4 includes the spin dependence of all QED processes and allows to perform a helicity-dependent tracking of particles through target and capture section. Starting with a cross-check, the synergy of these three codes allowed to specify the the parameters of a polarized positron source.

 
THPMN024 A Study for the Characterization of High QE Photocathodes 2760
 
  • D. Sertore, P. Michelato, L. Monaco, C. Pagani
    INFN/LASA, Segrate (MI)
  
  Funding: Work supported by the European Community, contract number RII3-CT-2004-506008

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.

 
THPMN025 High QE Photocathodes Performance during Operation at FLASH/PITZ Photoinjectors 2763
 
  • L. Monaco, P. Michelato, C. Pagani, D. Sertore
    INFN/LASA, Segrate (MI)
  • J. W. Baehr, M. Krasilnikov, S. Lederer, F. Stephan
    DESY Zeuthen, Zeuthen
  • J. H. Han, S. Schreiber
    DESY, Hamburg
  
  Funding: Work supported by the European Community, contract number RII3-CT-2004-506008

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.

 
THPMN029 A DC/Pulse Electron Gun with an Aperture Grid 2775
 
  • T. Sugimura, M. Ikeda, S. Ohsawa
    KEK, Ibaraki
  
  A new thermionic-electron gun for a high-brightness X-ray source is under development. Its extraction voltage and design current are 60 keV and 100 mA, respectively. In order to focus beams on a metal target within 1.0 x 0.1 mm2, it is required for the emittance of a beam to be small. A grid electrode is not an orthodox mesh grid but an aperture grid. An increase of the beam emittance and heat generation at a grid will be surpressed. Electrodes dimensions such as shape of Wehnelt electrode and a shape of an aperture grid are determined by the EGUN simulation and parameters were optimized. In this paper a result of beam examination will be reported.  
THPMN033 Commissioning a Cartridge-Type Photocathode RF Gun System at University of Tokyo 2787
 
  • A. Sakumi
    UTNL, Ibaraki
  • Y. Muroya, T. Ueda, M. Uesaka
    The University of Tokyo, Nuclear Professional School, Ibaraki-ken
  
  We have been developing a compact-sized cartridge-type cathode exchanging system installed in BNL-type IV photocathode RF gun. We can replace a cathode without breaking the vacuum of RF gun, so that a high quantum efficiency photocathode is not surrounded by oxygen or moisture. The advantage of this system can be controlled the quality of the each cathode by making cathode plugs in a factory. Moreover we can easily change a cathode material, such as visible light driven cathode (AgOCs NaK2Sb) the high QE cathode(Cs2Te) for high brightness beam, metal cathode(Mg) for ultra-fast phenomena. Therefore we can investigate characterization of variable cathode materials in high gradient electric field of ~100MV/m. The cavity with the exchanging port and the beam trajectory is calculated by superfish and GPT, respectively. We found that the parameters of the cavity with a plug is almost same compared with normal back plate. Using this system, we can investigate the cathode material and deliver the stable electron beam by one RF gun.  
THPMN036 Simulation Study on Attosecond Electron Bunch Generation 2796
 
  • K. Kan, T. Kondoh, J. Yang, Y. Yoshida
    ISIR, Osaka
  
  Pulse radiolysis, a stroboscopic method with an ultrashort electron bunch and an ultrashort light, is essential for the observation of ultrafast reactions. The time resolution of pulse radiolysis depends on the electron bunch length. In Osaka University, a 98-fs electron bunch was generated by using a photocathode electron linac for a development of femtosecond pulse radiolysis*. Furthermore, a sub-femtosecond/attosecond pulse radiolysis will be proposed to study the ionization and thermalization processes in attosecond time region. In order to realize such a high time resolution, the possibility of attosecond electron bunch generation based on the photocathode RF gun linac and a magnetic bunch compressor was studied. In the simulation, the bunch length growth due to charge, emittance, accelerating phase and magnetic fields were investigated to generate an attosecond electron bunch.

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

 
THPMN038 Dynamic Optical Modulation of the Electron Beam for the High Performance Intensity Modulated Radiation Therapy 2802
 
  • T. Kondoh, H. Kashima, J. Yang, Y. Yoshida
    ISIR, Osaka
  
  Radiation therapy attracts attention as one of cancer therapies nowadays. Recently, the radiation therapy of cancer is developing to un-uniform irradiation as IMRT, for reduce dose to normal tissue and concentrate dose to cancer tissue. A photo cathode RF gun is able to generate a low emittance electron beam pulse using a laser light pulse. We thought that a photo cathode RF gun can generate intensity modulated electron beam by optical modulation at the incident optics dynamically. Because of a low emittance, the modulated electron beam pulse is able to accelerate keeping shape. Accelerated electron pulses will be converted to X-ray pulses by a metal target bremsstrahlung method or by a laser inverse Compton scattering method. For the high performance intensity modulated radiation therapy (IMRT), dynamic optical modulation of the electron beam pulse were studied using a Photo cathode RF gun LINAC. Modulated and Moving electron beam will be reported.  
THPMN039 Femtosecond Electron Beam Dynamics in Photocathode Accelerator 2805
 
  • J. Yang, K. Kan, T. Kondoh, Y. Yoshida
    ISIR, Osaka
  
  Ultrashort electron beams, of the order of 100 fs, are essential to reveal the hidden dynamics of intricate molecular and atomic processes in nanofabrication through experimentation such as time-resolved electron diffraction and femto-chemistry. The transverse and longitudinal dynamics of ultrashort electron beam in a photocathode linear accelerator were studied for femtosecond electron beam generation. The emittance growth and bunch length increase due to the rf and the space charge effects in the rf gun were investigated with the laser injection phase. The dependences of the emittance, bunch length and energy spread on the bunch charge were measured experimentally and compared with the theoretical simulation. The increase of the bunch length due to the space charge effect was also investigated during the bunch compression in magnetic field.  
THPMN040 Development of an S-band Cs2Te-Cathode RF Gun with New RF Tuners 2808
 
  • 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
  
  We have been studying an S-band Cs2Te-Cathode RF Gun with 1.6 cells. The new gun cavity reported in this poster has new RF tuners, which are compact and, therefore, can be attached even on the half-cell. RF balance between the full- and half-cells is adjustable by using the tuners on both cells. Compared to the existing cavity, a Helicoflex seal for half-cell adjustment is not needed for new one. This structure is expected to have advantages for gun machining, for Q factor of the cavity, and for reduction of dark current from the RF gun. The cathode is made by evaporation on a Mo plug, and the plug is attached by a load lock system. We report status of the gun development.  
THPMN070 Development of a Full Scale Superconducting Undulator Module for the ILC Positron Source 2862
 
  • Y. Ivanyushenkov, E. Baynham, T. W. Bradshaw, A. J. Brummitt, F. S. Carr, A. J. Lintern, J. Rochford
    STFC/RAL, Chilton, Didcot, Oxon
  • I. R. Bailey, J. A. Clarke, J. B. Dainton, O. B. Malyshev, L. I. Malysheva, G. A. Moortgat-Pick, D. J. Scott
    Cockcroft Institute, Warrington, Cheshire
  • D. P. Barber
    DESY, Hamburg
  • P. Cooke
    Liverpool University, Science Faculty, Liverpool
  • B. J.A. Shepherd
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  
  Funding: This work is supported in part by the Commission of the European Communities under the 6th Framework Programme "Structuring the European Research Area", contract number RIDS-011899.

An undulator based positron source is a baseline for the International Linear Collider (ILC). The HeliCal collaboration in the UK is working on the development of a full scale 4-m long undulator module. Several prototypes have been built and tested in the R&D phase of the programme that culminated in the development of manufacturing techniques suitable for construction of the first full scale undulator sections. This paper details the design and the construction status of 4-m long undulator module.

 
THPMN071 Status of R&D on a Superconducting Helical Undulator for the ILC Positron Source 2865
 
  • Y. Ivanyushenkov, E. Baynham, T. W. Bradshaw, A. J. Brummitt, F. S. Carr, A. J. Lintern, J. Rochford
    STFC/RAL, Chilton, Didcot, Oxon
  • I. R. Bailey, J. A. Clarke, J. B. Dainton, O. B. Malyshev, L. I. Malysheva, G. A. Moortgat-Pick, D. J. Scott
    Cockcroft Institute, Warrington, Cheshire
  • D. P. Barber
    DESY, Hamburg
  • P. Cooke
    Liverpool University, Science Faculty, Liverpool
  • B. J.A. Shepherd
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  
  Funding: This work is supported in part by the Commission of the European Communities under the 6th Framework Programme "Structuring the European Research Area", contract number RIDS-011899.

An undulator based positron source is a baseline for the International Linear Collider (ILC). The HeliCal collaboration in the UK is carrying out an R&D programme on a short period supercoducting helical undulator with the goal to develop manufacturing technique as well as modelling and measurement techniques. Several undulator prototypes have been built and successfully tested. This paper summarizes the results of the R&D phase of the project.

 
THPMN090 Systematic Study of Undulator Based ILC Positron Source: Production and Capture 2918
 
  • W. Liu, W. Gai, K.-J. Kim
    ANL, Argonne, Illinois
  
  A systematic study of the positron production and capture systems for the undulator-based ILC positron source has been performed. Various undulator parameters, such as k and λ, were considered. Our model starts from the electron beam production of the polarized photons in the undulator section, photon transport and collimation in the drift section, and photon interaction on the target (titanium or tungsten). Next, our model transports the produced polarized positrons from the target, through the tapered capturing magnet, and through the normal conducting linac to several hundred MeV. Finally, the captured positrons meeting the damping ring emittance and energy spread requirements are accelerated up to 5 GeV using the standard ILC superconducting cavities. We will present parametric studies for the different scenarios (e.g. 60% polarization vs. unpolarized; target immersed in magnetic field vs. non-immersed) currently under consideration and report on the capturing yield and polarizations achieved for each.  
THPMN092 Design and Prototyping of the AMD for the ILC 2924
 
  • H. Wang, W. Gai, W. Liu
    ANL, Argonne, Illinois
  • A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio
  • T. Wong
    Illinois Institute of Technology, Chicago, Illinois
  
  The Adiabatic Matching Device (AMD), a tapered magnetic field with initial on-axis magnetic field up to 5 Tesla, is required in ILC positron capturing optics. An option of using a pulsed normal conducting structure based on flux concentrator technique can be used to generate high magnetic field*. By choosing the AMD geometry appropriately, one can shape the on-axis magnetic field profile by varying the inner shape of a flux concentrator. In this paper, we present an equivalent circuit model of a pulsed flux concentrator based on frequency domain analysis. The analysis shows a very good agreement with the experiment results from reference*. We have also constructed a prototype flux concentrator based on the circuit model, and experimental results are presented to verify the effectiveness of the model. Using the equivalent circuit model, a flux concentrator based AMD is designed for ILC positron matching. The beam capturing simulation results using the designed AMD are presented in this paper.

* H. Brechna, D. A. Hill and B. M. Bally, "150 KOe Liquid Nitrogen Cooled Flux Concentrator Magnet", Rev. Sci. Instr., 36 1529,1965.

 
THPMN097 Envelope and Multi-slit Emittance Measurements at Fermilab A0-Photoinjector and Comparison with Simulations 2936
 
  • C. M. Bhat, J.-P. Carneiro, R. P. Fliller, G. M. Kazakevich, J. K. Santucci
    Fermilab, Batavia, Illinois
  
  Funding: Operated by Universities Research Association, Inc. for the U. S. Department of Energy under contract DE-AC02-76CH03000.

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.

 
THPMN117 Design of a VHF-band RF Photoinjector with MegaHertz Beam Repetition Rate 2990
 
  • 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
  
  Funding: This work is supported by the Director, Office of Science, High Energy Physics, U. S. Dept. of Energy under Contract no. DE-AC02-05CH1121

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.

 
THPMS010 Polarized Pulsed Beam Source for Electron Microscopy 3011
 
  • N. Vinogradov, C. L. Bohn, P. Piot
    Northern Illinois University, DeKalb, Illinois
  • J. W. Lewellen, J. Noonan
    ANL, Argonne, Illinois
  
  A novel source of polarized pulsed electron beam is discussed. Unlike conventional devices based either on a thermionic cathodes or field-emission needle cathodes, in this source the electrons are produced by a laser beam hitting the cathode surface. Using a combination of gallium arsenide (GaAs) planar cathode and a suitable laser one can obtain a polarized picosecond electron bunch. Numerical simulations of the electron dynamics in the optimized cathode-anode geometry have shown that the beam with initial transverse size of a few mm can be focused down to 1 mm RMS at a distance of about 4 cm from the cathode. The suggested source can be installed instead of a tungsten filament source in an existing electron microscope with no modification of any column elements. The main advantages of this approach are that the beam can be easily pulsed, the beam is polarized which makes it an effective probe of some magnetic phenomena, and the laser can be used to provide larger beam intensity. The design of the source and subsequent fabrication has been completed. The paper presents numerical studies, conceptual design of the device, and results of beam measurements.  
THPMS014 Design of a High Field Stress, Velvet Cathode for the Flash X-Ray (FXR) Induction Accelerator 3023
 
  • T. L. Houck, C. G. Brown, D. E. Fleming, B. R. Kreitzer, K. E. Lewis, M. M. Ong, J. M. Zentler
    LLNL, Livermore, California
  
  Funding: This work was performed under the auspices of the U. S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

A new cathode design has been proposed for the Flash X-Ray (FXR) induction linear accelerator with the goal of lowering the beam emittance. The present design uses a conventional Pierce geometry and applies a peak field of 134 kV/cm (no beam) to the velvet emission surface. Voltage/current measurements indicate that the velvet begins emitting near this peak field value and images of the cathode show a very non-uniform distribution of plasma light. The new design has a flat cathode/shroud profile that allows for a peak field stress of 230 kV/cm on the velvet. The emission area is reduced by about a factor of four to generate the same total current due to the greater field stress. The relatively fast acceleration of the beam, approximately 2.5 MeV in 10 cm, reduces space charge forces that tend to hollow the beam for a flat, non-Pierce geometry. The higher field stress achieved with the same rise time is expected to lead to an earlier and more uniform plasma formation over the velvet surface. Simulations of the proposed design are presented.

 
THPMS021 Optimum Electron Bunch Creation in a Photoinjector Using Space Charge Expansion 3044
 
  • J. B. Rosenzweig, A. M. Cook, M. P. Dunning, R. J. England, P. Musumeci
    UCLA, Los Angeles, California
  • 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
  • S. M. Jones
    Jet Propulsion Laboratory, Pasadena, California
  
  Recent studies have shown that by illuminating a photocathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped electron bunch can be dynamically formed. Linear space-charge fields then exist in all dimensions inside of the bunch, which minimizes emittance growth. Here we study this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. We show that the two processes are compatible, with simulations indicating that a very high brightness beam can be obtained. An initial time-resolved experiment has been performed at the SPARC injector in Frascati, involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary experiment, as well as plans for future experiments to resolve the ellipsoidal bunch shape at low energy. Future measurements at high energy based on fs resolution RF sweepers are also discussed.  
THPMS060 Transport Optics Design and Multi-particle Tracking for the ILC Positron Source 3124
 
  • F. Zhou, Y. K. Batygin, Y. Nosochkov, J. Sheppard, M. Woodley
    SLAC, Menlo Park, California
  • W. Liu
    ANL, Argonne, Illinois
  
  Funding: U. S. DOE Contract DE-AC02-76SF00515

Undulator-based positron source is adopted as the International Linear Collider baseline design. Complete optics to transport the positron beam having large angular divergence and large energy spread from a thin Ti target to the entrance of the 5 GeV damping ring injection line is developed. Start-to-end multi-particle tracking through the beamline is performed including the optical matching device, capture accelerator system, transport system, superconducting booster linac, spin rotators, and energy compressor. Positron capture efficiency of different schemes (immersed vs shielded target, and flux concentrator vs quarter wave transformation for the optics matching system) is compared. For the scheme of a shielded target and quarter wave transformation, the simulation shows that 15.1% of the positrons from the target are captured within the damping ring 6-D acceptance at the entrance of the damping ring injection line.

 
THPMS061 Design of a High-current Injector and Transport Optics for the ILC Electron Source 3127
 
  • F. Zhou, Y. K. Batygin, A. Brachmann, J. E. Clendenin, R. H. Miller, J. Sheppard, M. Woodley
    SLAC, Menlo Park, California
  
  Funding: U. S. DOE Contract DE-AC02-76SF00515

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.

 
THPMS064 Lifetime Measurements of High Polarization Strained-Superlattice Gallium Arsenide at Beam Current > 1 Milliamp using a New 100kV Load Lock Photogun 3130
 
  • 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
  
  Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177.

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).

 
THPMS067 A CW Positron Source for CEBAF 3133
 
  • S. Golge, C. Hyde-Wright
    ODU, Norfolk, Virginia
  • A. Freyberger
    Jefferson Lab, Newport News, Virginia
  
  Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177.

A positron source for the 6 GeV (or the proposed 12 GeV upgrade) recirculating linacs at Jefferson Lab is presented. The proposed 100nA CW positron source has several unique characteristics; high incident beam power (100kW), 10 MeV incident electron beam energy, CW incident beam and CW production. Positron production with 10 MeV electrons has several advantages; the energy is below neutron threshold so the production target will not become activated during use and the absolute energy spread is bounded by the low incident energy. These advantages are offset by the large angular distribution of the outgoing positrons. Results of simulations of the positron production, capture, acceleration and injection into the recirculating linac are presented. Energy flow and thermal management of the production target present a challenge and are included in the simulations.

 
THPMS070 High Power Testing of a Fully Axisymmetric RF Gun 3142
 
  • H. Bluem
    AES, Princeton, New Jersey
  
  Funding: This work was funded under an SBIR contract from the US Department of Energy.

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.

 
THPMS095 Experimental Demonstration of Feasibility of a Polarized Gamma-source for ILC Based on Compton Backscattering Inside a CO2 Laser Cavity 3208
 
  • I. Pogorelsky, V. Yakimenko
    BNL, Upton, Long Island, New York
  
  Funding: Work supported by US Department of Energy contract DE-AC02-98CH10886

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)

 
FRXAB01 Status of High Polarization DC High Voltage GaAs Photoguns 3756
 
  • 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
  
  This talk will review the state of the art of high polarization GaAs photoguns used worldwide. Subject matter will include drive laser technology, photocathode material, gun design, vacuum requirements and photocathode lifetime as a function of beam current. Recent results have demonstrated high current, 85% polarized beams with high reliability and long lifetime under operational conditions. Research initiatives for ensuring production of high average and peak current beams for future accelerator facilities such as ELIC and the ILC will be also discussed.  
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