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Title: Development of a high average current polarized electron source with long cathode operational lifetime

Abstract

Substantially more than half of the electromagnetic nuclear physics experiments conducted at the Continuous Electron Beam Accelerator Facility of the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory) require highly polarized electron beams, often at high average current. Spin-polarized electrons are produced by photoemission from various GaAs-based semiconductor photocathodes, using circularly polarized laser light with photon energy slightly larger than the semiconductor band gap. The photocathodes are prepared by activation of the clean semiconductor surface to negative electron affinity using cesium and oxidation. Historically, in many laboratories worldwide, these photocathodes have had short operational lifetimes at high average current, and have often deteriorated fairly quickly in ultrahigh vacuum even without electron beam delivery. At Jefferson Lab, we have developed a polarized electron source in which the photocathodes degrade exceptionally slowly without electron emission, and in which ion back bombardment is the predominant mechanism limiting the operational lifetime of the cathodes during electron emission. We have reproducibly obtained cathode 1/e dark lifetimes over two years, and 1/e charge density and charge lifetimes during electron beam delivery of over 2?105???C/cm2 and 200 C, respectively. This source is able to support uninterrupted high average current polarized beam delivery to three experimental halls simultaneously formore » many months at a time. Many of the techniques we report here are directly applicable to the development of GaAs photoemission electron guns to deliver high average current, high brightness unpolarized beams.« less

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
899851
Report Number(s):
JLAB-ACT-07-558; DOE/ER/40150-4222
Journal ID: ISSN 1098-4402; TRN: US0702107
DOE Contract Number:  
AC05-84ER40150
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Special Topics. Accelerators and Beams; Journal Volume: 10; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ACCELERATORS; AFFINITY; BRIGHTNESS; CATHODES; CEBAF ACCELERATOR; CESIUM; CHARGE DENSITY; ELECTRON BEAMS; ELECTRON EMISSION; ELECTRON GUNS; ELECTRON SOURCES; ELECTRONS; LASERS; LIFETIME; NUCLEAR PHYSICS; OXIDATION; PHOTOCATHODES; PHOTOEMISSION; PHOTONS; POLARIZED BEAMS

Citation Formats

C. K. Sinclair, P. A. Adderley, B. M. Dunham, J. C. Hansknecht, P. Hartmann, M. Poelker, J. S. Price, P. M. Rutt, W. J. Schneider, and M. Steigerwald. Development of a high average current polarized electron source with long cathode operational lifetime. United States: N. p., 2007. Web. doi:10.1103/PhysRevSTAB.10.023501.
C. K. Sinclair, P. A. Adderley, B. M. Dunham, J. C. Hansknecht, P. Hartmann, M. Poelker, J. S. Price, P. M. Rutt, W. J. Schneider, & M. Steigerwald. Development of a high average current polarized electron source with long cathode operational lifetime. United States. doi:10.1103/PhysRevSTAB.10.023501.
C. K. Sinclair, P. A. Adderley, B. M. Dunham, J. C. Hansknecht, P. Hartmann, M. Poelker, J. S. Price, P. M. Rutt, W. J. Schneider, and M. Steigerwald. Thu . "Development of a high average current polarized electron source with long cathode operational lifetime". United States. doi:10.1103/PhysRevSTAB.10.023501. https://www.osti.gov/servlets/purl/899851.
@article{osti_899851,
title = {Development of a high average current polarized electron source with long cathode operational lifetime},
author = {C. K. Sinclair and P. A. Adderley and B. M. Dunham and J. C. Hansknecht and P. Hartmann and M. Poelker and J. S. Price and P. M. Rutt and W. J. Schneider and M. Steigerwald},
abstractNote = {Substantially more than half of the electromagnetic nuclear physics experiments conducted at the Continuous Electron Beam Accelerator Facility of the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory) require highly polarized electron beams, often at high average current. Spin-polarized electrons are produced by photoemission from various GaAs-based semiconductor photocathodes, using circularly polarized laser light with photon energy slightly larger than the semiconductor band gap. The photocathodes are prepared by activation of the clean semiconductor surface to negative electron affinity using cesium and oxidation. Historically, in many laboratories worldwide, these photocathodes have had short operational lifetimes at high average current, and have often deteriorated fairly quickly in ultrahigh vacuum even without electron beam delivery. At Jefferson Lab, we have developed a polarized electron source in which the photocathodes degrade exceptionally slowly without electron emission, and in which ion back bombardment is the predominant mechanism limiting the operational lifetime of the cathodes during electron emission. We have reproducibly obtained cathode 1/e dark lifetimes over two years, and 1/e charge density and charge lifetimes during electron beam delivery of over 2?105???C/cm2 and 200 C, respectively. This source is able to support uninterrupted high average current polarized beam delivery to three experimental halls simultaneously for many months at a time. Many of the techniques we report here are directly applicable to the development of GaAs photoemission electron guns to deliver high average current, high brightness unpolarized beams.},
doi = {10.1103/PhysRevSTAB.10.023501},
journal = {Physical Review Special Topics. Accelerators and Beams},
number = 2,
volume = 10,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}