Measurements of Cross-Field Thermal Conductivity in a Pure Electron Plasma

Cross-field thermal conductivity in a magnetized pure electron plasma is measured and found to be 10⁵ times larger than the value predicted using classical short-range collisions. The cylindrical plasma column of density n₀~10⁷ cm^-3 and temperature T~1 eV is confined in a Penning-Malmberg trap at B_z=12 kG giving r_c<<λ_D. Oscillating the column through a θ-symmetric electrostatic squeeze causes centrally-peaked separatrix dissipation, giving a centrally peaked T(r). The temperature profile is diagnosed by analyzing the number of particles that escape from the trap when the end confinement potential is lowered. The thermal diffusivity is calculated from the radial heat flux, Γ(r,t), which is derived from the time evolution of T(r,t). For plasmas with r_c<λ_D, heat transport is dominated by long-range collisions with impact parameter r_c<ρ<λ_D, rather than by classical short-range collisions with ρ<r_c. The measured thermal diffusivity is in close agreement with long-range collisional theory, as χ_L=0.49ν_cλ_D², and this is more than five orders of magnitude larger than classical diffusivity χ_c=(16π^1/2/15)ν_cr_c²ln(r_c/b).