A low-voltage retarding-field Mott polarimeter for photocathode characterization

Authors

J.L. McCarter, Thomas Jefferson National Accelerator Facility
M.L. Stutzman, Thomas Jefferson National Accelerator FacilityFollow
K.W. Trantham, Fort Hays State University
Timothy G. Anderson, University of Nebraska-LincolnFollow
A.M. Cook, Monmouth College
Timothy J. Gay, University of Nebraska - LincolnFollow

Date of this Version

2010

Citation

Nuclear Instruments and Methods in Physics Research A, Volume 618, Issues 1–3, 1–21 June 2010, Pages 30–36; doi:10.1016/j.nima.2010.02.123

Comments

Used by permission.

Abstract

Nuclear physics experiments at Thomas Jefferson National Accelerator Facility’s CEBAF rely on high polarization electron beams. We describe a recently commissioned system for prequalifying and studying photocathodes for CEBAF with a load-locked, low-voltage polarized electron source coupled to a compact retarding-field Mott polarimeter. The polarimeter uses simplified electrode structures and operates from 5 to 30 kV. The effective Sherman function for this device has been calibrated by comparison with the CEBAF 5 MeV Mott polarimeter. For elastic scattering from a thick gold target at 20 keV, the effective Sherman function is 0.201(5). Its maximum efficiency at 20 keV, defined as the detected count rate divided by the incident particle current, is 5.4(2)×10^-4, yielding a figure-of-merit, or analyzing power squared times efficiency, of 1.0(1)×10^-5. The operating parameters of this new polarimeter design are compared to previously published data for other compact Mott polarimeters of the retarding-field type.