Plasma ringing associated with pulsed resonance cones

Abstract

A temporal wave packet of frequency omega0(omegaci, omegapi<<omega0<<omegace, omegape) applied to a finite antenna in a magnetically confined plasma, is shown to excite an electrostatic field consisting of (1) a short-duration resonance cone and (2) a wave-like disturbance which follows afterward. This latter disturbance, which is related to the lower frequency mode of the delta-function induced transients discussed by Simonutti, persists long after the resonance cone. The phase factor associated with the disturbance is independent of omega0, and its constant-phase surfaces are lines which emanate from the antenna and make a small angle theta with respect to the confining magnetic field B. theta decreases with increasing time so that ''wavelengths'' perpendicular to B also decrease with increasing time. The correspondence of the fields obtained by wave-packet excitation to those obtained by both cw and delta-function excitations is discussed and experimental results are reported.