ENHANCEMENT OF H- PRODUCTION IN AN RF-DRIVEN MULTICUSP SOURCE

An rf-driven multicusp source has been operated in pulsed mode to generate H- ions that are formed by volume processes. A total H- current of approximately 40 mA has been extracted from a 5.6-mm-diam aperture with rf input power higher than 50 kW. Attempts have been made to enhance the H- beam current by introducing a small quantity of cesium vapor into the source chamber. It is found that the H- output current can be increased by a factor larger than 3 if some cesium is applied in the collar around the exit aperture. Electron current can be reduced by cesium deposition on the chamber walls. A simple cesium delivery system fabricated from small dispensers has been operated very successfully with the clean rf induction discharge.