Cyclotron Resonances in a Non-Neutral Multispecies Ion Plasma

Shifts of cyclotron mode frequencies away from the single particle $\Omega_c$ are observed to be proportional to the $E \times B$ rotation frequency in non-neutral ion plasmas. These cylindrical ion plasmas consist of Mg24$^+$, Mg25$^+$, and Mg26$^+$, with H$_3$O$^+$, O$_2^+$ and H$_2^+$ impurities. Laser cooling of the majority species, Mg24$^+$, enables temperature control over the range $10^{-5} < T < 1.$eV, as well as determination of cyclotron mode frequencies from launched wave absorption. At moderately low temperatures, the $m=1$ and $m=2$ cyclotron frequency shifts are well described by cold fluid theory for an equilibrium square profile.\footnote{E. Sarid, F. Anderegg and C.F. Driscoll, Phys. Plasmas {\bf 2}, 2895 (1995).} However, at $T < 10^{-3}$ eV centrifugal mass separation can cause order unity changes in these shifts. For $T \geq 1$ eV, the observed frequency shifts are reduced substantially. Prior high temperature experiments$^1$ saw majority species shifts consistent with cold fluid theory, and theoretically unexplained minority species shifts $\Delta f \sim 2f_{\mathrm Dio}$. Comparisons will be made with nascent theory to determine the effects of temperature and profile shape on these cyclotron modes.