CHARACTERISTICS OF A SURFATRON DRIVEN ION-SOURCE

A small, lightweight ion source based on a surface-wave sustained plasma is investigated. Previously designed to be a 2 mA, 3 keV krypton ion launcher in an on board spacecraft experiment, its operation is extended to several common gases at various operating frequencies and extraction voltages. It is built around a fused silica discharge tube that has one end fitted with a two-grid extraction system. This tube is enclosed by a surface-wave launcher (surfatron) operated between 750 and 1000 MHz, and the discharge is sustained with only 35 W. The beam is neutralized by electrons emitted by a tungsten filament. Ion current densities extracted at a few kilovolts lie in the range 10-40 mA/cm2, depending upon the gas used. The largest ion current is obtained with hydrogen: 8.5 mA at 5 kV. Variations in the source performances with the gases used are analyzed using the "beam relative perveance" concept and the surfatron equivalent circuit model.