Low-frequency azimuthally propagating (diocotron) waves in a non-neutral electron beam column

Naturally occurring and externally driven stable low‐frequency (6–500 kHz) oscillations have been observed for an electron beam column. Experimental data are presented for oscillations of 357 kHz (natural) and 181 kHz (driven). Phase shift measurements using six azimuthal probes spaced 60° apart show that the oscillations correspond to l=1 diocotron waves.