Cyclotron resonance in a pure electron plasma column

We demonstrate experimentally the effects of plasma rotation and particle thermal velocities on cyclotron resonance in a long cylindrical pure electron plasma column of low density (${\mathrm{\omega }}_{\mathit{p}}^2$≪${\mathrm{\omega }}_{\mathit{c}}^2$). A single m=1 mode (${\mathit{e}}^{\mathit{i}\mathit{m}\mathrm{\theta }\mathrm{-}\mathit{i}\mathrm{\omega }\mathit{t}}$) is found whose frequency ω is down-shifted from ${\mathrm{\omega }}_{\mathit{c}}$=eB/${\mathit{m}}_{\mathit{e}}$ by an amount equal to the low-frequency diocotron mode frequency (〈${\mathrm{\omega }}_{\mathit{p}}^2$〉/2${\mathrm{\omega }}_{\mathit{c}}$). For m=2,3,4,. . . sets of modes are found which are Doppler shifted upward from ${\mathrm{\omega }}_{\mathit{c}}$. We explain these as radially trapped and azimuthally propagating Bernstein modes.