Milliampere Beam Studies using High Polarization Photocathodes at the CEBAF Photoinjector

Conference · Sun Apr 01 00:00:00 EDT 2018 · PoS PSTP2017

DOI:https://doi.org/10.22323/1.324.0014· OSTI ID:1467040

Grames, Joseph M. ^[1]; Adderley, Philip A. ^[1]; Hansknecht, John C. ^[1]; Poelker, Matthew ^[1]; Moser, Daniel G. ^[1]; Stutzman, Marcy L. ^[1]; Zhang, Shukui ^[1]

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1. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

Extending the charge lifetime of today's spin polarized GaAs photoelectron guns from tens to thousands of Coulombs is a requirement for long-duration operation at milliampere beam current. There are two main approaches frequently considered to achieve this goal. The first is improving photo-gun vacuum, which provides a direct means to minimize the ill effects of ion bombardment and associated QE decay. In this contribution, we demonstrate the second: enhancing the charge lifetime at milliampere beam current by using large laser spots which serves to distribute ion damage over a larger region of the photocathode. The efficacy of this approach was presented at past workshops, but using bulk GaAs and green laser light without RF structure. In this contribution, highly polarized beam was produced from strained-superlattice GaAs/GaAsP photocathodes inside the 130 kV photo-gun at the CEBAF photoinjector, at beam currents from 0.5 to 1.5 mA and with a clear indication of lifetime enhancement using laser beams as large as ~8 mm2. However, when the laser beam size was increased beyond this diameter, further lifetime enhancement was not observed which highlights the importance of proper cathode/anode design to maintain loss-free beam delivery and the preservation of static vacuum conditions. In addition, this contribution presents electron beam polarization measurements at currents to 1 mA.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1467040
• Report Number(s): JLAB-ACC-18-2784; DOE/OR/23177-4516
• Journal Information: PoS PSTP2017, Conference: 17th International Workshop on Polarized Sources, Targets, and Polarimetry (PSTP2017) : Kaist, South Korea, October 16-20, 2017
• Country of Publication: United States
• Language: English