Radial Dependence of HF Wave Field Strength in the BPD Column

Abstract

Several detailed beam/plasma investigation programs have “been conducted in the large vacuum chamber of the Space Environment Simulation Laboratory (SESL) at the NASA Johnson Space Center. In particular, the experiments of Bernstein et al. (1979) show that at a critical electron beam current an instability, the Beam Plasma Discharge (BPD), between the beam and the ambient plasma develops. The BPD onset shows a dramatic change in the light emission, RF spectrum, and beam/plasma electron velocity distribution. Rationale for studying this instability has been generally established in view of describing beam experiments aboard sounding rockets, from the SESL plasma chamber work, and proposed for Shuttle missions. It has been noted in Jost et al. (1980) that an increase in energy by as much as a factor of two, exists for a fraction of the primary beam particles. For the laboratory research with keV beam energies this corresponds to an energy increase of a few keV. Electric field strengths of volts/m must be present within the discharge column to accelerate primary beam electrons by that amount, however, previous work did not isolate the particular waves in RF spectra during BPD that contained volts/m field strengths.