Development of a duoplasmatron ion source at the Ithemba laboratory for accelerator based science (ithemba labs)

Abstract

A cold hollow cathode duoplasmatron ion source has been designed, built, optimized and evaluated for use as an external stand-by ion source for the second injector cyclotron (SPC2) during those times that the light-ion injector cyclotron (SPCl) is out of operation and not available for neutron-therapy and the production of radioisotopes, as well as for the Van de Graaff accelerator. In comparison with more elaborate sources a cold cathode source is compact, of small mass, uncomplicated in terms of its construction and easy to operate. It was therefore important to verify whether this type of source can be used for the present application, for which proton beams with intensities of more than 200 μA are required, before the construction of more complex sources should be endeavored. Since it is difficult to predict the behavior of ion sources by calculation alone, it was considered imperative to build a duoplasmatron source in order to evaluate it experimentally, and at the same time to study the physical processes which occurs in ion sources theoretically, in order to enhance our understanding of the observed source behaviour. The computer program OPERA-3d was used for numerical field calculations and a detailed study of the influence of different operating parameters on the extracted beam current was done to determine the optimum operating conditions of the duoplasmatron ion source. The results lead to a conclusion that more complex and elaborate ion source designs should be considered, because a cold hollow cathode duoplasmatron ion source does not satisfy the beam intensity requirements of neutrontherapy and production of radioisotopes at iThemba LABS.