Charge and fluence lifetime measurements of a dc high voltage GaAs photogun at high average current

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GaAs-based dc high voltage photoguns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed high average current facilities that must operate at tens of milliamperes or more. This paper describes techniques to maintain good vacuum while delivering beam, and techniques that minimize the ill effects of ion bombardment, the dominant mechanism that reduces photocathode yield of a GaAs-based dc high voltage photogun. Experimental results presented here demonstrate enhanced lifetime at high beam currents by: (a) operating with the drive laser beam positioned away from the electrostatic center ... continued below

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3501 (12 pages); Other: CC BY

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J. Grames, R. Suleiman, P.A. Adderley, J. Clark, J. Hansknecht, D. Machie, M. Poelker, M.L. Stutzman April 1, 2011.

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GaAs-based dc high voltage photoguns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed high average current facilities that must operate at tens of milliamperes or more. This paper describes techniques to maintain good vacuum while delivering beam, and techniques that minimize the ill effects of ion bombardment, the dominant mechanism that reduces photocathode yield of a GaAs-based dc high voltage photogun. Experimental results presented here demonstrate enhanced lifetime at high beam currents by: (a) operating with the drive laser beam positioned away from the electrostatic center of the photocathode, (b) limiting the photocathode active area to eliminate photoemission from regions of the photocathode that do not support efficient beam delivery, (c) using a large drive laser beam to distribute ion damage over a larger area, and (d) by applying a relatively low bias voltage to the anode to repel ions created within the downstream beam line. A combination of these techniques provided the best total charge extracted lifetimes in excess of 1000 C at dc beam currents up to 9.5 mA, using green light illumination of bulk GaAs inside a 100 kV photogun.

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3501 (12 pages); Other: CC BY

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  • Journal Name: Phys.Rev.ST Accel.Beams; Journal Volume: 14; Journal Issue: 04

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  • Report No.: JLAB-ACC-11-1344
  • Report No.: DOE/OR/23177-1548
  • Grant Number: AC05-06OR23177
  • DOI: 10.1103/PhysRevSTAB.14.043501 | External Link
  • Office of Scientific & Technical Information Report Number: 1013124
  • Archival Resource Key: ark:/67531/metadc836197

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  • April 1, 2011

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  • May 19, 2016, 3:16 p.m.

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  • Aug. 3, 2016, 2:57 p.m.

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J. Grames, R. Suleiman, P.A. Adderley, J. Clark, J. Hansknecht, D. Machie, M. Poelker, M.L. Stutzman. Charge and fluence lifetime measurements of a dc high voltage GaAs photogun at high average current, article, April 1, 2011; Newport News, Virginia. (digital.library.unt.edu/ark:/67531/metadc836197/: accessed September 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.