Search

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.

An atomic hydrogen source, designed to operate in the viscous flow range, has been built at BNL. A unique feature of this source is a miniature gap between a teflon tube which guides the beam and an accommodator which cools it. Across this gap a stepfunction in temperature, with the teflon temperature exceeding 100°K and the accommodator temperature below 8°K, was successfully maintained. This configuration collimates the beam enough to prevent significant diffusive losses without subjecting it to the temperature range of high recombination. Initial results with an orifice of only one-tenth the dissociator aperture are indicative of particle density in the beam of well above 1010 cm-3.