Recent trends in the design of large RF, microwave and ECR ion sources for the production of broad ion beams

Abstract

Recently there have been considerable interest in the application of large RF, microwave and ECR ion sources for the production of monoenergetic ion beams of very large cross-section dedicated to specific surface treatments and modification of materials. We recall the recent trends and novel concepts in the design of these different classes of ion sources. Studies involving the production of singly charged, high density inert or reactive ion beams are described. Particular attention is given to the beam homogeneity and to the production of low energy ion beams. Different kinds of acceleration-deceleration systems including sets of parallel wires are presented and their respective figures of merit outlined. Optimization of the microwave power coupling to the plasma is presented in the case of circular or rectangular waveguides ionization chambers and circular vacuum tight windows which are the most vulnerable part of the ions source. As far as protection of the window against deposited films, backstreaming electron bombardment and overheating is concern, we describe the resonant slit in a metallic diagram located downstream the window. This simple component gives a very significant improvement of the microwave coupling and its lifetime.