Ion beams in multi-species plasmas

Abstract

Argon and xenon ion velocity distribution functions are measured in Ar-He, Ar-Xe, and Xe-He expanding helicon plasmas to determine if ion beam velocity is enhanced by the presence of lighter ions. Contrary to observations in mixed gas sheath experiments, we find that adding a lighter ion does not increase the ion beam speed. The predominant effect is a reduction of ion beam velocity consistent with increased drag arising from increased gas pressure under all conditions: constant total gas pressure, equal plasma densities of different ions, and very different plasma densities of different ions. These results suggest that the physics responsible for the acceleration of multiple ion species in simple sheaths is not responsible for the ion acceleration observed in expanding helicon plasmas.

Laser induced fluorescence diagnostic for velocity distribution functions: applications, physics, methods and developments

“…4.5.1. Ar II and Ar I. Argon remains one of the most common gas in use in the plasma physics community, partly due to its low cost, it is also by far the lightest noble gas with a metastable ion state available for single photon LIF diagnostics, making it one of the most common candidates in a multi-ion-species kinetics related investigation [11][12][13]119]. Before diode laser based LIF is popularized, a common LIF Ar II scheme was to excite the 3d′ 2 G 9/2 →4p′ 2 F 0 7/2 transition with a 611.66 nm (in vacuum) laser and receive the 461.08 nm fluorescence from the 4p′ 2 F 0 7/2 →4s′ 2 D 5/2 decay.…”