Temperature and anisotropic-temperature relaxation measurements in cold, pure-electron plasmas

Abstract

Plasma temperatures in the range 25 to 2×106 K have been measured using a cryogenic, ultra-high vacuum, pure-electron plasma trap. The rate ν at which the temperatures parallel and perpendicular to the applied magnetic field relax to a common value has been measured over the temperature range 28 to 3.8×105 K and the magnetic field range 20 to 60 kG. This rate ν is closely related to the plasma collision frequency. When the cyclotron radius rc is large compared to the classical distance of closest approach b (rc/b≫1), the measured values of ν are in agreement with conventional collision theory. When the cyclotron radius is small compared to the classical distance of closest approach (rc/b≪1), ν drops precipitously as rc/b is decreased, in agreement with the many-electron adiabatic invariant theory of O’Neil and Hjorth.