Development and characterization of a directional molecular flow generator for 50-200 eV ion-beam surface neutralization

This paper describes and characterizes a directional molecular flow generator based on low-energy ion-beam transport and grazing-incidence surface neutralization. The device combines a multi-electrode electrostatic transport assembly for long-distance beam collimation and staged deceleration with a high-aspect-ratio rectangular-channel tungsten neutralizer. Experiments were performed with He and Ar at a fixed microwave power of 500 W. The peak ion current densities measured by a Faraday cup over the investigated inlet-pressure ranges were 0.35-1.09 μA/mm2 for the He-based beam and 0.17-0.47 μA/mm2 for the Ar-based beam. The downstream directional-flow response, represented by an effective half-angle inferred from axial pressure-decay measurements, was 2.06° for He and 4.31° for Ar at Vp = 200 V, increasing to 11.31° and 17.35°, respectively, at Vp = 80 V under the fixed-pressure voltage scan. The retarding-potential analyzer measured the axial energy distribution of the ion beam; the kinetic-energy distribution of the neutralized beam and the absolute neutral-particle flux were not independently measured. The neutralizer open-area ratio was ∼0.5, and η = 0.98 was used only as an adopted model parameter for a geometrical flux estimate. These results establish the transport and directional-flow response of the integrated device under He and Ar operation. Although the present experiments were conducted using He and Ar, the DMFG architecture is designed to be adaptable to atmospheric species such as N2 and O2; operation with these reactive gases remains to be experimentally validated and will require gas-specific assessment of ion composition, surface condition, neutralization behavior, neutral-beam energy, and absolute flux.