Stability of non-neutral plasma in a magnetic dipole trap

A non-neutral plasma can be confined in a global thermal equilibrium state as well as a local

thermal equilibrium along magnetic field lines in a magnetic dipole trap [1]. While global ther-

mal equilibrium states are maximum entropy states and hence guaranteed to be stable, local

thermal equilibria can support growing diocotron modes [2]. These modes were studied to a

great extend in the homogeneous magnetic field of a Penning-Malmberg trap [3]. We will focus

on the inhomogeneous magnetic field of a z-pinch, which serves as an approximation of the

vicinity of a levitated coil. This implies two differences in comparison to a Penning-Malmberg

trap. First, grad-B and curvature drifts influence the mode. Second, arbitrary non-neutrality can be

studied. In particular, different fractions of electrons and positrons are considered. This study is

motivated by APEX, "A Positron-Electron eXperiment" in a levitated dipole trap [4].