Faraday Cup Designs for High Efficiency Determination of Energy- and Angular-Resolved Charged Particle Fluxes
Presented at Utah Research on Capitol Hill, January 31, 2013.
Faraday cups provide a simple and efficient apparatus to measure the absolute magnitude of charge particle fluxes, and with the addition of a retarding field analyzer and defining apertures the capability to determine the energy and angular distributions of the fluxes. Through careful design of the electron optics, a Faraday cup can be tailored to meet specific requirements for detector size, minimum detectable flux, collection efficiency, absolute accuracy, energy discrimination, and angular resolution. This work explores design concepts through electric field and charged particle trajectory simulations, theoretical analysis, and evaluation of experimental prototypes to develop compact, high efficiency Faraday cups capable of a range of energy and angular resolutions. The designs rely of high efficiency Faraday cups coupled with grid-free Einzel lens energy analyzers for nearly energy-independent determination of absolute fluxes. We also review specific designs and applications of these Faraday cup detectors to electron emission and transport studies, spacecraft charging applications and electron beam characterization measurements done in conjunction with various projects conducted by the Materials Physics Group.