STUDIES ASSOCIATED WITH THE DEVELOPMENT OF A MODIFIED UNIVERSITY-OF-AARHUS NEGATIVE-ION SOURCE

A high intensity negative ion source, based in principle on a source developed at the University of Aarhus, has been designed and constructed. This source demonstrates a high degree of reliability, operational stability and long lifetime. The plasma generation mechanism produces a uniform plasma density and thus uniform sputter probe wear. The results of studies associated with the source development are given which establish relationships between negative ion yield and certain operation parameters - principally oven temperature and sputter probe voltage. The parameters for maximizing yields from a number of elemental materials were observed to occur at oven temperatures of ∼ 200°C and sputter probe voltages between -900 and -1200 V depending upon the cathode material. Negative ion yields are observed to increase with sputter probe voltage according to a theoretically predictable V 5 2 law. The important design aspects of the source and negative ion yields observed to-date are given. Application of the Langmuir-Saha theory is made to the yield data and changes in work function necessary to produce observed negative ion yields are computed. The measured changes in work function agree in several instances with the theoretical formulation of Broeder et al.22). © 1979.