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Title: Performance of GAASP/GAAS Superlattice Photocathodes in High Energy Experiments using Polarized Electrons

Abstract

The GaAsP/GaAs strained superlattice photocathode structure has proven to be a significant advance for polarized electron sources operating with high peak currents per microbunch and relatively low duty factor. This is the characteristic type of operation for SLAC and is also planned for the ILC. This superlattice structure was studied at SLAC [1], and an optimum variation was chosen for the final stage of E-158, a high-energy parity violating experiment at SLAC. Following E-158, the polarized source was maintained on standby with the cathode being re-cesiated about once a week while a thermionic gun, which is installed in parallel with the polarized gun, supplied the linac electron beams. However, in the summer of 2005, while the thermionic gun was disabled, the polarized electron source was again used to provide electron beams for the linac. The performance of the photocathode 24 months after its only activation is described and factors making this possible are discussed.

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
876757
Report Number(s):
SLAC-PUB-11711
TRN: US0601313
DOE Contract Number:
AC02-76SF00515
Resource Type:
Conference
Resource Relation:
Conference: Contributed to 11th International Workshop on Polarized Sources and Targets (PST05), Tokyo, Japan, 14-17 Nov 2005
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; CATHODES; ELECTRON BEAMS; ELECTRON SOURCES; ELECTRONS; LINEAR ACCELERATORS; PARITY; PERFORMANCE; PHOTOCATHODES; STANFORD LINEAR ACCELERATOR CENTER; SUPERLATTICES; TARGETS; THERMIONICS; Accelerators,ACCPHY, PHYS

Citation Formats

Brachmann, A., Clendenin, J.E., Maruyama, T., Garwin, E.L., Ioakemidi, K., Prescott, C.Y., Turner, J.L., /SLAC, Prepost, R., and /Wisconsin U., Madison. Performance of GAASP/GAAS Superlattice Photocathodes in High Energy Experiments using Polarized Electrons. United States: N. p., 2006. Web.
Brachmann, A., Clendenin, J.E., Maruyama, T., Garwin, E.L., Ioakemidi, K., Prescott, C.Y., Turner, J.L., /SLAC, Prepost, R., & /Wisconsin U., Madison. Performance of GAASP/GAAS Superlattice Photocathodes in High Energy Experiments using Polarized Electrons. United States.
Brachmann, A., Clendenin, J.E., Maruyama, T., Garwin, E.L., Ioakemidi, K., Prescott, C.Y., Turner, J.L., /SLAC, Prepost, R., and /Wisconsin U., Madison. Mon . "Performance of GAASP/GAAS Superlattice Photocathodes in High Energy Experiments using Polarized Electrons". United States. doi:. https://www.osti.gov/servlets/purl/876757.
@article{osti_876757,
title = {Performance of GAASP/GAAS Superlattice Photocathodes in High Energy Experiments using Polarized Electrons},
author = {Brachmann, A. and Clendenin, J.E. and Maruyama, T. and Garwin, E.L. and Ioakemidi, K. and Prescott, C.Y. and Turner, J.L. and /SLAC and Prepost, R. and /Wisconsin U., Madison},
abstractNote = {The GaAsP/GaAs strained superlattice photocathode structure has proven to be a significant advance for polarized electron sources operating with high peak currents per microbunch and relatively low duty factor. This is the characteristic type of operation for SLAC and is also planned for the ILC. This superlattice structure was studied at SLAC [1], and an optimum variation was chosen for the final stage of E-158, a high-energy parity violating experiment at SLAC. Following E-158, the polarized source was maintained on standby with the cathode being re-cesiated about once a week while a thermionic gun, which is installed in parallel with the polarized gun, supplied the linac electron beams. However, in the summer of 2005, while the thermionic gun was disabled, the polarized electron source was again used to provide electron beams for the linac. The performance of the photocathode 24 months after its only activation is described and factors making this possible are discussed.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Feb 27 00:00:00 EST 2006},
month = {Mon Feb 27 00:00:00 EST 2006}
}

Conference:
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  • Spin-polarized electron photoemission has been studied for GaAs/GaAs{sub 1-x}P{sub x} strained superlattice cathodes grown by gas-source molecular beam epitaxy. The superlattice structural parameters are systematically varied to optimize the photoemission characteristics. The heavy-hole and light-hole transitions are reproducibly observed in quantum efficiency spectra, enabling direct measurement of the band energies and the energy splitting. Electron-spin polarization as high as 86% with over 1% quantum efficiency has been observed.
  • GaAs-GaAsP and InGaAs-AlGaAs strained-layer superlattice photocathodes are presented as emission sources for highly polarized electron beams. The GaAs-GaAsP cathode achieved a maximum polarization of 92({+-}6)% with a quantum efficiency of 0.5%, while the InGaAs-AlGaAs cathode provides a higher quantum efficiency (0.7%) but a lower polarization [77({+-}5)%]. Criteria for achieving high polarization using superlattice photocathodes are discussed based on experimental spin-resolved quantum efficiency spectra.
  • Spin-polarized electron photoemission has been studied for GaAs/GaAs{sub 1-x}P{sub x} strained superlattice cathodes grown by gas-source molecular beam epitaxy. The superlattice structural parameters are systematically varied to optimize the photoemission characteristics. The heavy-hole and light-hole transitions are reproducibly observed in quantum efficiency spectra, enabling direct measurement of the band energies and the energy splitting. Electron-spin polarization as high as 86% with over 1% quantum efficiency has been observed.
  • Spin-polarized electron photoemission has been studied for GaAs/GaAs{sub 1-x}P{sub x} strained superlattice cathodes grown by gas-source molecular beam epitaxy. The superlattice structural parameters are systematically varied to optimize the photoemission characteristics. The heavy-hole and light-hole transitions are reproducibly observed in quantum efficiency spectra, enabling direct measurement of the band energies and the energy splitting. Electron-spin polarization as high as 86% with over 1% quantum efficiency has been observed.
  • A new GaAs DC high voltage load lock photogun has been constructed at Jefferson Laboratory (JLab), with improved vacuum and photocathode preparation capabilities. As reported previously, this gun was used to study photocathode lifetime with bulk GaAs at DC beam currents between 1 and 10 mA. In this submission, lifetime measurements were performed using high polarization strained-superlattice GaAs photocathode material at beam currents up to 1 mA, with near bandgap light from a fiber based drive laser having picosecond optical pulses and RF time structure.