Simulations of electrostatic modes of nonneutral plasmas with small aspect ratio in a Penning trap

The dependence on induced charge, experimental geometry, and temperature of electrostatic modes in very low aspect ratio non-neutral plasmas in a Penning trap is considered. The modes are of interest as non-destructive diagnostics of the shape of the plasmas. These investigations include equilibrium calculations of plasma shapes and profiles at finite temperature and particle-in-cell simulations of axisymmetric modes. The results of the simulations are compared to the zero-temperature theory by Dubin ͓Phys. Rev. Lett. 66, 2076 ͑1991͔͒ taken to first-order in the aspect ratio and to experimental measurements by Weimer et al. ͓Phys. Rev. A 49, 3842 ͑1994͔͒. In general, it is concluded that the Dubin theory provides a means to obtain reasonable estimates of plasma parameters, including density, radius, and axial length, for plasmas in the very important regime for which the axial length is comparable to the Debye length. In addition, dependence on induced charge, equilibrium shape, and plasma temperature are identified which can likely be used to improve agreement between theory and experiment.