Francisco Valerio 2020
Abstract
Electron gun high voltage conditioning data analysis
Francisco Valerio-Lopez (Benemerita Universidad Autonoma de Puebla, Puebla, Mexico 72592) Carlos Hernandez-Garcia (Thomas Je↵erson National Accelerator Facility, Newport News, VA 23606).
Field emission is a process in which a metal surface emits electrons due to the pres- ence of a high electrostatic field. Even after the best polishing and cleaning practices, field emission from particulates and nano-protrusions is the primary mechanism limiting maximun achievable bias voltage in DC high voltage photoemission electron guns used at Je↵erson Lab. Gas high voltage conditioning eliminates field emission from electrode cathodes used in these guns. It is a lengthy and delicate process that if not done carefully may lead to catastrophic failure. Furthermore, its behavior and success depends on elec- trode geometry. Several electrodes of various shapes have been high voltage conditioned over the past few years, but the amount of data for each conditioning run makes the analysis of the conditioning process very di�cult. In this work, thousands of data points collected for each conditioning run were analyzed to characterize each electrode shape in regards to field emission onset voltage, cumulative processing time, maximum voltage required to eliminate field emission, and field emission activity. An algorithm was made in Python capable of reading and filtering the raw data. Three electrode shapes have been analyzed; Tee with no shield electrode at the ceramic-electro interface, large shield electrode, and small shield electrode. Both shielded electrodes were designed for 200kV operation compared to the 100 kV Tee electrode. Knowing the behavior of high voltage conditioning will serve as a baseline about expected behavior, as a guide in designing future electron guns and for planning the length of time required in their high voltage conditioning phase.