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Title: Quantum efficiency temporal response and lifetime of a GaAs cathode in SRF electron gun

Abstract

RF electron guns with a strained super lattice GaAs cathode can generate polarized electron beam of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface. In a normal conducting RF gun, the extremely high vaccum required by these cathodes can not be met. We report on an experiment with a superconducting SRF gun, which can maintain a vacuum of nearly 10-12 torr because of cryo-pumping at the temperature of 4.2K. With conventional activation, we obtained a QE of 3% at 532 nm, with lifetime of nearly 3 days in the preparation chamber. We plan to use this cathode in a 1.3 GHz 1/2 cell SRF gun to study its performance. In addition, we studied the multipacting at the location of cathode. A new model based on the Forkker-Planck equation which can estimate the bunch length of the electron beam is discussed in this paper. Future particle accelerators such as eRHIC and ILC require high brightness, high current polarized electrons Recently, using a superlattice crystal, the maximum polarization of 95% was reached. Activation with Cs,O lowers the electron affinity and makes it energetically possible for all the electrons excited in tomore » the conduction band and reach the surface to escape into the vacuum. Presently the polarized electron sources are based on DC gun, such as that at the CEBAF at Jlab. In these devices, the life time of the cathode is extended due to the reduced back bombardment in their UHV conditions. However, the low accelerating gradient of the DC guns lead to poor longitudinal emittance. The higher accelerating gradient of the RF gun generates low emittance beams. Superconducting RF guns combine the excellent vacuum conditions of the DC guns with the higher accelerating gradients of the RF guns and provide potentially a long lived cathode with very low transverse and longitudinal emittance. In our work at BNL, we successfully activated the GaAs. The quantum efficient is 3% at 532 nm and is expected to improve further. In addition, we studied the multipacting at the location of cathode. A new model based on the Forkker-Planck equation which can estimate the bunch length of the electron beam is discussed in this paper.« less

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) Relativistic Heavy Ion Collider
Sponsoring Org.:
DOE - Office Of Science
OSTI Identifier:
1013488
Report Number(s):
BNL-90777-2010-CP
R&D Project: KBCH139; KB0202011; TRN: US1102487
DOE Contract Number:  
DE-AC02-98CH10886
Resource Type:
Conference
Resource Relation:
Conference: First International Particle Accelerator Conference (IPAC) 2010; Kyoto, Japan; 20100523 through 20100528
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ACCELERATORS; AFFINITY; BNL; BRIGHTNESS; CATHODES; ELECTRON BEAMS; ELECTRON GUNS; ELECTRON SOURCES; ELECTRONS; LIFETIME; PERFORMANCE; POLARIZATION; QUANTUM EFFICIENCY; SUPERLATTICES; relativistic heavy ion collider

Citation Formats

Wang, E, Ben-Zvi, I, Kewisch, J, Burrill, A, Rao, T, Wu, Q, and Holmes, D. Quantum efficiency temporal response and lifetime of a GaAs cathode in SRF electron gun. United States: N. p., 2010. Web.
Wang, E, Ben-Zvi, I, Kewisch, J, Burrill, A, Rao, T, Wu, Q, & Holmes, D. Quantum efficiency temporal response and lifetime of a GaAs cathode in SRF electron gun. United States.
Wang, E, Ben-Zvi, I, Kewisch, J, Burrill, A, Rao, T, Wu, Q, and Holmes, D. Sun . "Quantum efficiency temporal response and lifetime of a GaAs cathode in SRF electron gun". United States. https://www.osti.gov/servlets/purl/1013488.
@article{osti_1013488,
title = {Quantum efficiency temporal response and lifetime of a GaAs cathode in SRF electron gun},
author = {Wang, E and Ben-Zvi, I and Kewisch, J and Burrill, A and Rao, T and Wu, Q and Holmes, D},
abstractNote = {RF electron guns with a strained super lattice GaAs cathode can generate polarized electron beam of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface. In a normal conducting RF gun, the extremely high vaccum required by these cathodes can not be met. We report on an experiment with a superconducting SRF gun, which can maintain a vacuum of nearly 10-12 torr because of cryo-pumping at the temperature of 4.2K. With conventional activation, we obtained a QE of 3% at 532 nm, with lifetime of nearly 3 days in the preparation chamber. We plan to use this cathode in a 1.3 GHz 1/2 cell SRF gun to study its performance. In addition, we studied the multipacting at the location of cathode. A new model based on the Forkker-Planck equation which can estimate the bunch length of the electron beam is discussed in this paper. Future particle accelerators such as eRHIC and ILC require high brightness, high current polarized electrons Recently, using a superlattice crystal, the maximum polarization of 95% was reached. Activation with Cs,O lowers the electron affinity and makes it energetically possible for all the electrons excited in to the conduction band and reach the surface to escape into the vacuum. Presently the polarized electron sources are based on DC gun, such as that at the CEBAF at Jlab. In these devices, the life time of the cathode is extended due to the reduced back bombardment in their UHV conditions. However, the low accelerating gradient of the DC guns lead to poor longitudinal emittance. The higher accelerating gradient of the RF gun generates low emittance beams. Superconducting RF guns combine the excellent vacuum conditions of the DC guns with the higher accelerating gradients of the RF guns and provide potentially a long lived cathode with very low transverse and longitudinal emittance. In our work at BNL, we successfully activated the GaAs. The quantum efficient is 3% at 532 nm and is expected to improve further. In addition, we studied the multipacting at the location of cathode. A new model based on the Forkker-Planck equation which can estimate the bunch length of the electron beam is discussed in this paper.},
doi = {},
url = {https://www.osti.gov/biblio/1013488}, journal = {},
number = ,
volume = ,
place = {United States},
year = {2010},
month = {5}
}

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