Cyclotron resonance phenomena in a non-neutral multispecies ion plasma

Cyclotron modes of a non-neutral Mg ion plasma were studied in a long cylindrical PenningMalmberg trap. Several modes with angular dependence exp(iZ@, 12 1, are observed near the cyclotron frequencies of the various Mg ions. The I= 1 modes for the majority species are downshifted from the cyclotron frequencies, with downshifts as large as four times the diocotron frequency. These large shifts are quantitatively explained by a multispecies cold-plasma theory, including the dependence on the plasma size and composition. These dependencies allow the plasma size and composition to be obtained from the measured mode frequencies. In contrast, the I= 1 downshifts for minority species are generally close to twice the diocotron frequency, and remain unexplained. Cyclotron heating of the plasma ions was also observed with a surprising effect of improving the plasma confinement. 0 I.995 American Institute of Physics.