Cyclotron mode frequencies and resonant absorption in multi-species ion plasmas

摘要

Cyclotron mode frequencies are studied on trapped rigid-rotor multi-species ion plasmas. Collective effects and radial electric fields shift the mode frequencies away from the "bare" cyclotron frequencies 2 pi F-c((s)) (q(s)B/M(s)c) for each species s. These frequency shifts are measured on the distinct cyclotron modes (m = 0, 1, and 2) with cos(m theta) azimuthal dependence. We find that for radially uniform plasmas the frequency shifts corroborate a simple theory expression, in which collective effects enter only through the E x B rotation frequency f(E) and the species fraction delta(s). The m = 1 center-of-mass mode is in agreement with a simple "clump" model. Additionally, ultra-cold ion plasmas exhibit centrifugal separation by mass, and additional frequency shifts are observed, in agreement with a more general theory. (C) 2015 AIP Publishing LLC.