Particle-in-cell simulations of radio frequency discharge scenarios for initiation of multipole plasma trap experiments

The multipole plasma trap (MPT) [1] is a three-dimensional confinement volume bounded by an envelope of radio-frequency (RF) electrodes. In this work, scenarios for initiating a plasma discharge within the MPT are investigated via particle-in-cell (PIC) simulations using the VSim 11 software package [2], to accomplish in situ generation of trapped particles. Spherical and cylindrical electrode geometries are considered, and neutral gas may be puffed into the trapping volume to commence the RF discharge. The discharge may also be aided by directing an electron beam from an external source into the MPT volume. The evolution of the discharge over many RF periods is studied, with particular attention to diffusion of the trapped plasma across the confinement boundary. The progression of the discharge is optimized in simulation in order to inform and streamline the experimental approach to a similar MPT configuration. The inclusion of a variable multicusp magnetic field (via electromagnetic coils co-located with the RF electrodes) is explored as a means of modifying the electron loss rate, and neutral gas pressures consistent with negative ion production in an electronegative discharge are considered as well.

[1] N. K. Hicks, A. Bowman, and K. Godden, Physics 1 (3), 392–401 (2019) doi:10.3390/physics1030028

[2] C. Nieter and J. R. Cary, J. Comput. Phys. 196, 448 (2004)