2011 Particle Accelerator Conference - Classification: Advanced Concepts and Future Directions / Tech 02: Lepton Sources

Paper	Title	Page
MOP128	An Optimized X-band Photoinjector Design for the LLNL MEGa-Ray Project	334
	S.G. Anderson, F. Albert, C.P.J. Barty, G.A. Deis, C.A. Ebbers, D.J. Gibson, F.V. Hartemann, T.L. Houck, R.A. Marsh LLNL, Livermore, California, USA C. Adolphsen, A.E. Candel, E.N. Jongewaard, Z. Li, C. Limborg-Deprey, T.O. Raubenheimer, S.G. Tantawi, A.E. Vlieks, F. Wang, J.W. Wang, F. Zhou SLAC, Menlo Park, California, USA
	Funding: This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. We present an optimized 5 + ½ cell, X-band photoinjector designed to produce 7 MeV, 250 pC, sub-micron emittance electron bunches for the LLNL Mono-Energetic Gamma-Ray (MEGa-Ray) light source. This LLNL/SLAC collaboration modifies a design previously demonstrated to sustain 200 MV/m on-axis accelerating fields. We discuss the photoinjector operating point, optimized by scaling beam dynamics from S-band photo-guns and by evaluation of the MEGa-Ray source requirements. The RF structure design is presented along with the current status of the photoinjector construction and testing. A.E. Vlieks, et al., High Energy Density and High Power RF: 6th Workshop, AIP, CP691, p. 358 (2003).

MOP155	Progress on Diamond Amplified Photo Cathode	382
	E. Wang PKU/IHIP, Beijing, People's Republic of China I. Ben-Zvi, X. Chang, J. Kewisch, E.M. Muller, T. Rao, J. Smedley, Q. Wu BNL, Upton, Long Island, New York, USA T. Xin Stony Brook University, Stony Brook, USA
	Funding: Work supported by Brookhaven science Associates, LLC Contract No.DE-AC02-98CH10886 with the U.S.DOE Two years ago, we obtained an emission gain of 40 from the Diamond Amplifier Cathode (DAC) in our test system. In our current systematic study of hydrogenation, the highest gain we registered in emission scanning was 178. We proved that our treatments for improving the diamond amplifiers are reproducible. Upcoming tests planned include testing DAC in a RF cavity. Already, we have designed a system for these tests using our 112 MHz superconducting cavity, wherein we will measure DAC parameters, such as the limit, if any, on emission current density, the bunch charge, and the bunch length.

MOP156	Status of the Polarized SRF Photocathode Gun Design	385
	J.H. Park, H. Bluem, M.D. Cole, D. Holmes, T. Schultheiss, A.M.M. Todd AES, Princeton, New Jersey, USA I. Ben-Zvi, J. Kewisch, E. Wang BNL, Upton, Long Island, New York, USA
	Funding: This work was supported by the U.S. Department of Energy, under Contract No. DE-FG02-06ER84450. A polarized SRF photocathode gun is being considered as a high-brightness electron injector for the International Linear Collider (ILC). The conceptual engineering analysis and design of this injector, which is required to deliver a large emittance ratio, is presented. The delivered beam parameters we predict are compared to the required performance after the ILC damping ring. The analysis indicates that it may be possible to save cost by eliminating the damping ring though higher values of the emittance ratio are still to be demonstrated.

MOP157	Testing a GAAS Cathode in SRF Gun	388
	E. Wang, I. Ben-Zvi, A. Burrill, J. Kewisch, T. Rao, Q. Wu BNL, Upton, Long Island, New York, USA D. Holmes AES, Medford, NY, USA
	Funding: Work supported by Brookhaven science Associates, LLC Contract No.DE-AC02-98CH10886 with the U.S.DOE RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode’s surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1⁄2 cell SRF gun, the vacuum can be maintained at nearly 10^-12 Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun.

MOP158	Numerical Study of Plasma Wakefields Excited by a Train of Electron Bunches	391
	Y. Fang, P. Muggli USC, Los Angeles, California, USA C. Huang LANL, Los Alamos, New Mexico, USA W.B. Mori UCLA, Los Angeles, California, USA
	Funding: Work supported by the US department of Energy We study numerically the excitation of plasma wakefields by a train of electron bunches using the UCLA particle-in-cell code Quickpic. We aim to find an optimal regime that combines both the advantages of linear and non-linear plasma wakefield accelerator. On one hand, the longitudinal electric field excited by individual bunches add as in the linear region, and the transformer ratio can be maximized (i.e. much larger than 2) by adjusting the number of particles in the bunches as well as their distance. On the other hand, the bunches create large wakefield independent of transverse sizes evolution while propagating through the plasma as in the non-linear region. In principle, such a scheme can multiply the energy of the witness bunch following the drive bunch train in a single plasma wakefield accelerating stage. The parameters for electron bunches are chosen based on the current experiment at the Brookhaven National Laboratory Accelerator Test Facility (ATF), where this scheme can be tested. Detailed simulation results will be presented. C. Huang, J. Comp. Phys.

Paper

Title

Page

An Optimized X-band Photoinjector Design for the LLNL MEGa-Ray Project

334

S.G. Anderson, F. Albert, C.P.J. Barty, G.A. Deis, C.A. Ebbers, D.J. Gibson, F.V. Hartemann, T.L. Houck, R.A. Marsh
LLNL, Livermore, California, USA
C. Adolphsen, A.E. Candel, E.N. Jongewaard, Z. Li, C. Limborg-Deprey, T.O. Raubenheimer, S.G. Tantawi, A.E. Vlieks, F. Wang, J.W. Wang, F. Zhou
SLAC, Menlo Park, California, USA

Funding: This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
We present an optimized 5 + ½ cell, X-band photoinjector designed to produce 7 MeV, 250 pC, sub-micron emittance electron bunches for the LLNL Mono-Energetic Gamma-Ray (MEGa-Ray) light source. This LLNL/SLAC collaboration modifies a design previously demonstrated to sustain 200 MV/m on-axis accelerating fields*. We discuss the photoinjector operating point, optimized by scaling beam dynamics from S-band photo-guns and by evaluation of the MEGa-Ray source requirements. The RF structure design is presented along with the current status of the photoinjector construction and testing.
*A.E. Vlieks, et al., High Energy Density and High Power RF: 6th Workshop, AIP, CP691, p. 358 (2003).

MOP155

Progress on Diamond Amplified Photo Cathode

382

E. Wang
PKU/IHIP, Beijing, People's Republic of China
I. Ben-Zvi, X. Chang, J. Kewisch, E.M. Muller, T. Rao, J. Smedley, Q. Wu
BNL, Upton, Long Island, New York, USA
T. Xin
Stony Brook University, Stony Brook, USA

Funding: Work supported by Brookhaven science Associates, LLC Contract No.DE-AC02-98CH10886 with the U.S.DOE
Two years ago, we obtained an emission gain of 40 from the Diamond Amplifier Cathode (DAC) in our test system. In our current systematic study of hydrogenation, the highest gain we registered in emission scanning was 178. We proved that our treatments for improving the diamond amplifiers are reproducible. Upcoming tests planned include testing DAC in a RF cavity. Already, we have designed a system for these tests using our 112 MHz superconducting cavity, wherein we will measure DAC parameters, such as the limit, if any, on emission current density, the bunch charge, and the bunch length.

MOP156

Status of the Polarized SRF Photocathode Gun Design

385

J.H. Park, H. Bluem, M.D. Cole, D. Holmes, T. Schultheiss, A.M.M. Todd
AES, Princeton, New Jersey, USA
I. Ben-Zvi, J. Kewisch, E. Wang
BNL, Upton, Long Island, New York, USA

Funding: This work was supported by the U.S. Department of Energy, under Contract No. DE-FG02-06ER84450.
A polarized SRF photocathode gun is being considered as a high-brightness electron injector for the International Linear Collider (ILC). The conceptual engineering analysis and design of this injector, which is required to deliver a large emittance ratio, is presented. The delivered beam parameters we predict are compared to the required performance after the ILC damping ring. The analysis indicates that it may be possible to save cost by eliminating the damping ring though higher values of the emittance ratio are still to be demonstrated.

MOP157

Testing a GAAS Cathode in SRF Gun

388

E. Wang, I. Ben-Zvi, A. Burrill, J. Kewisch, T. Rao, Q. Wu
BNL, Upton, Long Island, New York, USA
D. Holmes
AES, Medford, NY, USA

Funding: Work supported by Brookhaven science Associates, LLC Contract No.DE-AC02-98CH10886 with the U.S.DOE
RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode’s surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1⁄2 cell SRF gun, the vacuum can be maintained at nearly 10^-12 Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun.

MOP158

Numerical Study of Plasma Wakefields Excited by a Train of Electron Bunches

391

Y. Fang, P. Muggli
USC, Los Angeles, California, USA
C. Huang
LANL, Los Alamos, New Mexico, USA
W.B. Mori
UCLA, Los Angeles, California, USA

Funding: Work supported by the US department of Energy
We study numerically the excitation of plasma wakefields by a train of electron bunches using the UCLA particle-in-cell code Quickpic*. We aim to find an optimal regime that combines both the advantages of linear and non-linear plasma wakefield accelerator. On one hand, the longitudinal electric field excited by individual bunches add as in the linear region, and the transformer ratio can be maximized (i.e. much larger than 2) by adjusting the number of particles in the bunches as well as their distance. On the other hand, the bunches create large wakefield independent of transverse sizes evolution while propagating through the plasma as in the non-linear region. In principle, such a scheme can multiply the energy of the witness bunch following the drive bunch train in a single plasma wakefield accelerating stage. The parameters for electron bunches are chosen based on the current experiment at the Brookhaven National Laboratory Accelerator Test Facility (ATF), where this scheme can be tested. Detailed simulation results will be presented.
* C. Huang, J. Comp. Phys.