Excitation of the l=2 azimuthal mode in a pure electron plasma

The effect of an externally imposed time-varying quadrupole electrostatic perturbation on a pure electron plasma trapped in a Malmberg-Penning trap is investigated experimentally. A resonance occurs when the frequency of the drive matches the frequency of the azimuthal l=2, kz=0 mode. Very good agreement is found between the experimentally determined resonance frequency and the real part of the frequency calculated from a two-dimensional linear model for a top-hat density profile, while nonlinear deviations for the mode amplitude are found especially close to the resonance.