NIMROD simulations of the stabilization of the FRC tilt instability with energetic ion beams

The hybrid kinetic-MHD option [Charlson C. Kim, Phys. Plasmas, {\bf15}, 072507 (2008)] in the NIMROD code [C.R. Sovinec, et al., J. Comp. Phys. {\bf195}, 355 (2004)] has been extended to optionally employ a full-orbit, full-f PIC advance. In addition, a current coupling option has been added where the particles are coupled to the fluid through the J x B term in the momentum equation, rather than through the pressure tensor. As an initial test, simulations were performed to compare with previous calculations that investigated the stabilization of the field-reversed configuration (FRC) tilt instability with energetic ion beams [D.C. Barnes and R.D. Milroy, Phys. Fluids B {\bf3}, 2609 (1991)]. FRC parameters were adjusted to duplicate those of the previous study, and the energetic particles were found to stabilize the n=1 mode at an almost identical beam threshold as was found earlier. While the previous study did not include higher order modes, initial results with NIMROD suggest that an n=3 mode may be driven by the energetic particles for these parameters. Further studies investigate scaling to different machine sizes and study FRC profile modifications due to the beams presence.