Confinement and manipulation of non-neutral plasmas using rotating wall electric fields

Abstract

A “rotating wall” perturbation technique enables confinement of up to 3×109 electrons or 109 ions in Penning–Malmberg traps for periods of weeks. These rotating wall electric fields transfer torque to the particles by exciting Trivelpiece–Gould plasma modes with kz≠0 and mθ=1 or 2. Modes that rotate faster than the plasma column provide a positive torque that counteracts the background drags, resulting in radial plasma compression or steady-state confinement in near-thermal equilibrium states. Conversely, modes that rotate slower than the plasma provide a negative torque, and enhanced plasma expansion is observed. The observed Trivelpiece–Gould mode frequencies are well predicted by linear, infinite-length, guiding-center theory.