Development of Multiampere Negative Ion Sources

The Neutral Beam Development Group at BNL is developing H-/D-surface plasma sources as part of a high energy neutral beam injector. Uncooled Penning and magnetron sources have operated at a maximum beam current of 1 A (10 ms pulses, Mk III) and a maximum pulse length of 200 ms (0.3 A, Mk IV). A magnetron source with focusing grooves on the cathode and an asymmetric anode-cathode geometry operates at a power efficiency of 8 kW/A and a 6% gas efficiency. As the next step, a water cooled magnetron, designed to give a steady state beam of 1-2 A, has been constructed. In initial tests in the hydrogen mode, we have obtained a steady state discharge current of 8 A at 500 V. In addition, experiments are in progress to test a modification of the magnetron which may significantly improve its performance. By injecting a sheet of plasma, produced by a highly gas efficient hollow cathode discharge, into a magnetron type anode-cathode geometry, we anticipate a reduction of the source operating pressure by at least three orders of magnitude. Initial experiments have given indications of H-production. The next plasma injection experiment is designed to give a steady state beam of ¿ 1 A.