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 (ωₚ² ≪ ω꜀²). A single m=1 mode (e^(imθ - iωt)) is found whose frequency ω is down-shifted from ω꜀ = eB/mₑ by an amount equal to the low-frequency diocotron mode frequency (〈ωp²〉/2ω꜀). For m = 2,3,4,. . . sets of modes are found which are Doppler shifted upward from ωc. We explain these as radially trapped and azimuthally propagating Bernstein modes.