Landau damping of electron plasma waves in the linear and trapping regimes

Abstract

Linear Landau damping and nonlinear wave-particle trapping oscillations are observed with mθ=0 standing plasma waves (Trivelpiece-Gould modes) in a trapped pure electron plasma. The measured linear damping rate (10−3≲γ/ω≲10−1) agrees quantitatively with Landau damping theory for moderate plasma temperatures (1<T<3 eV), and exceedingly low wave amplitudes (δn/n<10−6). At larger amplitudes, the wave initially damps at the Landau rate, then develops trapping oscillations at frequency ωtr, causing the effective damping rate to decrease with amplitude as first predicted by O’Neil in 1965. For comparison, the measured damping rate is observed to decrease dramatically when the resonant particles are eliminated by truncating the nominally Maxwellian velocity distribution.