MEASUREMENT OF NEGATIVE-ION-PRODUCTION EFFICIENCIES AND DEVELOPMENT OF A DC OPERATION SPUTTER-TYPE NEGATIVE-ION SOURCE

For the development of a high current heavy negative ion source, the production efficiency of the negative ions by Xe+ sputtering with cesium and electron detachment cross sections in xenon gas were measured. The maximum efficiency for Cu- was 12.1% and the single-electron detachment cross section was found to be of the order of 0.6-1.4 x 10(-15) cm2 in the energy range of 5-50 keV. Based on the results of these fundamental experiments, a plasma-sputter-type heavy negative ion source has been constructed, in which the plasma was generated at a rf-frequency of 13.56 MHz. A total negative ion current of 2.5 mA was obtained without electrons from the source in dc operation, and the Cu- current was detected to be 91% of the total beam. The operation characteristics are described.