Advances in DC photocathode electron guns Page: 1 of 10
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ADVANCES IN DC PHOTOCATHODE
B. M. Dunham, P. Hartmann, R. Kazimi, H. Liu, B.M. Poelker, J.S. Price,
P.M. Rutt, W.J. Schneider, and C.K. Sinclair
Thomas Jefferson National Accelerator Facility
12000 Jefferson Ave, Newport News, VA 23606
Abstract. At Jefferson Lab, a DC photoemission gun using GaAs and GaAs-like cathodes provides
a source of polarized electrons for the main accelerator. The gun is required to produce high average
current with long operational lifetimes and high system throughput. Recent work has shown that
careful control of the parameters affecting cathode lifetime lead to dramatic improvements in source
operation. These conditions include vacuum and the related effect of ion backbombardment, and
precise control of all of the electrons emitted from the cathode. In this paper, we will review recent
results and discuss implications for future photocathode guns.
At Jefferson Lab, a DC photoemission gun using GaAs and GaAs-like cathodes
provides polarized electrons for the main accelerator. DC guns hold a distinct
advantage for systems that require high average current as opposed to those requiring
high peak current with a low duty factor. The polarized source runs at 100 kV and can
provide multiple, independent beams to three experimental halls with a total average
current of up to 200 pA and can deliver as much as 16 C of electrons per day.
The ability to deliver these high average currents for extended periods of time has
a large impact on machine availability at Jefferson Lab. On the main accelerator, 70-
80% availability is necessary to meet the full experimental schedule of the nuclear
physics community so little time can be spent on cathode maintenance. Progress has
been made in the last year in understanding and controlling the conditions that affect
cathode lifetime: vacuum, crystal damage from ion backbombardment, and precise
control of halo electrons. The polarized source now routinely reaches operational 1/e
lifetimes of 100-200 hours for -150 pA average beam currents and upgrades are being
planned to increase this to over 500 hours.
In this paper, recent results from the polarized source will be presented showing
details leading to dramatic improvements in the operational lifetime of the source.
Properties related to the performance of future photocathode guns will be discussed.
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Dunham, Bruce M.; Heartmann, P.; Kazimi, Reza; Liu, Hongxiu; Poelker, B. M.; Price, J. S. et al. Advances in DC photocathode electron guns, article, July 1, 1998; Newport News, Virginia. (digital.library.unt.edu/ark:/67531/metadc703754/m1/1/: accessed November 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.