Scanning multiple collector electrostatic analyzer with application to plasma potential measurement

Abstract

Three collector electrodes have been located accurately on the focal plane of a parallel-plate electrostatic energy analyzer to form an exit slit matched to a large inlet slit by the design magnification ratio. In bench tests with a nearly uniform, monoenergetic K+ beam at 5 kV these collectors have been found to provide a scanning capability for measurement of the energy of such a large beam with sufficient precision, ΔV/V∼±10 -3, to resolve plasma potential in heavy ion probe diagnostic studies of magnetically confined plasmas. In such studies a wide entrance slit is needed because of low signal levels. The method provides enhanced resolution with greater facility than obtainable with a feedback approach used in prior investigations. A nearly triangular sharply peaked profile was observed on the center collector providing the desired resolution. Scans at various entrance angle settings have been made and beam size and peak location results compared with predictions based on the existing model for an ideal instrument.