Non-neutral Plasma in a Magnetic Dipole Field

Uniquely in plasma physics, non-neutral plasmas can approach global thermal equilibrium states. In linear traps this is due to cylindrical symmetry and the conservation of canonical angular momentum. Equivalently, in a rotating frame, a non-neutral plasma in a uniform magnetic field sees an effective potential well centered on the symmetry axis. We seek global thermal equilibrium states in the dipole magnetic field, which shares some symmetry properties with linear traps. Recent theory work identified the conditions under which such equilibria exist. We perform electron plasma experiments in a supported magnet trap and in a levitated dipole trap. In both experiments, we observe a toroidally propagating plasma wave that bears the signatures of a dipole version of the diocotron mode commonly observed in linear traps. Both experiments feature wall probe diagnostics. The potential on the magnet can be controlled in both experiments. In the levitated dipole an electron beam probe is directed along the axis of the dipole and employed to monitor the time-dependent potential created by the electron plasma. These experiments aim, in part, to determine whether the predicted thermal equilibrium states are experimentally accessible.