Materials exposed to electron bombardment can charge positively or negatively, depending on the number of electrons ejected from the material. This electron emission is the main mechanism which drives spacecraft charging, which can induce electrostatic breakdown of insulators and damage pertinent electrical, optical, and mechanical components. The electron yield (ratio of emitted to incident electrons) is an intrinsic property which characterizes how a material will charge under these types of conditions. However electron yield of insulators is very difficult to measure because measurement causes charge buildup.
To measure the intrinsic yield (yield of uncharged material) of insulators new methods have been developed which minimize incident charge using a pulsed beam, analyze the emitted electron energy distribution using an improved hemispherical grid retarding field analyzer, and neutralize acquired charge using UV and low-energy electron flooding. Modifications were made to the instrumentation to increase electron measurement efficiency, and improve charge neutralization techniques. New analysis methods produced an increased signal-to-noise ratio and allowed for measurement of yield for charges as small as 30 electrons (~ 5 attocoulombs). Various tests were performed to validate the changes made and quantify the improvement. These new methods give high-accuracy absolute yield measurements because they allow for the measurement of all incident and emitted charges. The improved charge neutralization methods allow for yield measurement with negative and positive charging. Results of validation tests and measurements of extreme insulator yield are presented.
* Supported by a Utah NASA Space Grant Consortium Graduate Fellowship.
Available at: http://works.bepress.com/justin_christensen/8/