Compact Scanning Retarding Potential Analyzer

A miniature scanning electrostatic energy analyzer has been developed for measurements of the ion energy distribution in low-pressure plasma discharges. The retarding potential analyzer utilizes four grids to reject the incident electron flux and discriminate the ion energy. It features a compact size of 5-mm diameter and 2.5-mm thickness and uses a simple configuration to mount the grids and provide voltage isolation using high temperature ceramic cement that avoids complicated grid alignment or MEMS fabrication techniques. Mounting on a fast-scanning two-axis probe drive eliminates overheating of the ceramics and subsequent current leakage, which permits insertion into challenging locations and provides profiles of the ion energy in the plasma discharge. Guidelines for the analyzer design for high density operation are discussed, and the performance of the analyzer is shown for measurements in a hollow cathode plume in xenon plasmas.