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{}ωc²). A single m=1 mode (e^imθ-iωt) is found whose frequency {ω} is down-shifted from ωc=eB/mₑ by an amount equal to the low-frequency diocotron mode frequency (〈ωₚ²〉/2ωc). 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.