An optimized Faraday cage design for electron beam current measurements

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Abstract
Describes a Faraday cage detector for measuring electron beam intensity for use with energies up to 1.2 MeV, with the present data taken at 100 keV. The design features a readily changeable limiting aperture and detector cup geometry, and a secondary electron suppression grid. The detection efficiency of the cage is shown to be limited only by primary backscatter through the detector solid angle of escape, which is optimized with respect to primary backscattered electrons and secondary electron escape. The geometry and stopping material of the detection cup are varied, and the results show that for maximum detection efficiency with carbon as the stopping material, the solid angle of escape must be equal to or less than 0.05 pi sr. The experimental results are consistent within the +or-2% accuracy of the detection electronics, and are not limited by the Faraday cage detection efficiency.