Investigations of the physical properties of photoemission polarized electron sources for accelerator applications
Dunham, Bruce Matthew
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https://hdl.handle.net/2142/21511
Description
Title
Investigations of the physical properties of photoemission polarized electron sources for accelerator applications
Author(s)
Dunham, Bruce Matthew
Issue Date
1993
Doctoral Committee Chair(s)
Cardman, Lawrence S.
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Elementary Particles and High Energy
Language
eng
Abstract
This experiment measured the polarization and quantum efficiency as a function of wavelength for the chalcopyrite semiconductor Zn(Ge$\rm\sb{0.7}Si\sb{0.3})As\sb2.$ Also, the onset of space charge growth of a 100 keV electron beam passing through the Illinois/CEBAF polarized electron injection system was studied by measuring the beam emittance as a function of current. Finally, the thermal properties of GaAs were investigated by measuring the beam emittance as functions of the excitation laser wavelength and the laser spot size.
The experiments were performed at the University of Illinois Nuclear Physics Laboratory using a 100 keV photoemission polarized electron gun, a electron spin manipulation system of a novel design, a Mott polarimeter, and an emittance measuring system. The design and performance of the entire system is described.
The maximum polarization of Zn(Ge$\rm \sb{0.7}Si\sb{0.3})As\sb2$ was measured to be $\sim$19%, much lower than the expected 100%. Also, the expected transition of the polarization through zero was not observed. The beam emittance as a function of current was measured and the onset of space charge effects was found to be $\sim$0.5 mA, much lower than predicted by the electron gun design program scEGUN. Finally, the effective transverse thermal energy of the electrons emitted from GaAs at 100 keV as a function of excitation wavelength was measured by a new method for low beam currents. The electron thermal energy for wavelengths between 840 and 633 nm was found to be $\sim$33 meV, a factor of 3 lower than for a thermionic electron gun. It was also found to increase sharply for photon wavelengths less than 633 nm.
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