Studies of an expansion-type tandem rf bucket source

A new rf source producing a large and uniform plasma with magnetic field-free geometry for neutral beam has been developed. The source consists of a small-diameter multiple-rf plasma generator and a bucket chamber as a plasma expansion section. The plasma density scaling, the spatial profile, and the ion beam extraction have been studied by using the single rf plasma generator. It was found that under the optimized conditions the plasma density and the profile in the expanded plasma were essentially ruled by qualities of the bucket chamber itself. The present rf source is promising for the application of large-volume positive-ion source or plasma processing.