Wave absorption measurements of the electron distribution in the Space Physics Simulation Chamber

High resolution measurements of electron distributions in laboratory plasmas can give needed insight into fundamental questions of plasma behavior. For example, upcoming experiments in NRL's Space Physics Simulation Chamber (SPSC) will investigate the kinetic plasma physics of chirped whistler-mode chorus emissions and wave-particle interactions that are predicted to play a significant role in the dynamics of Earth's radiation belts. Preliminary SPSC experiments investigate two diagnostic techniques: electrostatic energy analyzers and wave absorption. Because whistler-mode waves are absorbed by Doppler-shifted cyclotron resonant electrons and the amount of absorption is related to the number of resonant electrons, wave absorption uses low-amplitude whistler-mode waves to measure parallel electron velocity distributions. In our analysis of preliminary data, we relax the assumption that the background velocity distribution is Maxwellian so that we can use wave absorption in both equilibrium and non-equilibrium plasmas. Additionally, the interference produced by multiple simultaneously propagating probe wave modes is mitigated using Fourier analysis. In ongoing experiments, we are bench-marking energy analyzer and wave absorption techniques and exploring radiation-belt physics in the SPSC.