Investigation of Surface Ionization Detector for Cesium Oven Evaporation Rate

Abstract

To assure stable cesium injection for negative ion source, the surface ionization detector (SID) is applied for diagnosis. Consisted of emitter and collector, the SID is operating based on bias voltage setting to drive the ionized cesium ions from emitter to the collector for detection. An analysis model of SID for cesium oven evaporation rate is established, investigating the process of cesium transportation in vacuum, thermionic ionization and cesium ion collection. Cesium transportation from nozzle to SID in vacuum is studied on the basis of free molecule flow model, and the cesium density distribution is obtained after having estimated cesium flux density ratio intercepted by SID from nozzle. The collection period is analyzed by particle tracking model, providing the relationship of SID current and ionized cesium current under adaptive bias voltage along with characteristics between SID current and bias voltage reproduced corresponding to experimental results. The model is adjustable and flexible to deal with different 3D structures, geometry and electric field setting. SID analysis for cesium oven of HUST negative ion source is carried out to monitor oven operation and to provide evaporation rate features under various oven temperatures along with error analysis.