Performance characteristics of a multiple-sample, cesium-sputter, negative ion source

A multiple-sample, cesium-sputter, negative-ion source which permits sample changes without disruption of on-line tandem electrostatic accelerator operations is described. The source is equipped with provisions for remotely selecting and moving into the beam position any one of 60 samples by means of stepping motors equipped with absolute shaft encoders. A spherical-sector cesium ionizer is used to produce the cesium beam for sputtering the sample material. The source is equipped with a three-element electrode system which has been designed to increase the perveance for cesium ion beam generation and to improve negative ion beam extraction from the source. Details of the mechanical design features and optics of the three-element electrode system are presented. Data pertinent to source operation and the dependence of negative ion yields on certain source operational parameters are also given. (orig.)