Electron Beam Injection Method for Determining Plasma Frequency and Electron Density

A method for the direct measurement of plasma frequency from a detected electron beam in the Caltech ice dusty plasma experiment [1] is being investigated. Adapting a method of Shirakawa [2], an electron beam will be generated from an emissive tungsten filament and injected into a weakly (10^-6) ionized plasma with cold (~190 K) neutrals. This beam should generate electron plasma waves excited by the two-stream instability. The waves would then be detected by a separate receiving probe in the plasma. This method overcomes several limitations of the conventional Langmuir probe method (e.g., thin-film deposition, uncertain calibration), and removes the dependence on plasma ionic composition for computing electron density. The probe is under construction and results will be presented at the meeting and compared to other methods.

[1] Kil-Byoung Chai and Paul Bellan. Spontaneous formation of nonspherical water ice grains in a plasma environment, GRL. 40, 6258 (2013)

[2] Teruyuki Shirakawa and Hideo Sugai. Plasma Oscillation Method for Measurements of Absolute Electron Density in Plasma, Japanese J. Appl. Phys., 32, 5129 (1993)