Parameter dependence of two-fluid and finite Larmor radius effects on the Rayleigh-Taylor instability in finite beta plasmas

Abstract

The parameter dependence of two-fluid and finite Larmor radius (FLR) effects on the Rayleigh-Taylor (RT) instability in finite beta plasmas is examined based on extended magnetohydrodynamic (MHD) models. Four MHD models, the MHD model, two-fluid MHD model, MHD model with FLR effects, and two-fluid MHD model with FLR effects, are compared with each other with local and eigenmode analyses. For equilibria with nonuniform magnetic fields, the absence of complete stabilization of large wavenumber modes due to the FLR effect [Zhu et al., Phys. Rev. Lett. 101, 085005 (2008)] occurs for beta lower than the critical value for a small pressure gradient. For the two-fluid MHD model with the FLR term, it is shown that the absence of complete stabilization occurs for the beta different from that for the MHD model with the FLR term, the mode is not always most stable among those for the other models, depending on beta, and the coupling between RT mode and electron drift wave appears. The spatial dependence of the local analysis is examined in comparison with that of eigenfunctions. For the case of MHD with the FLR term, for large wavenumber modes, the growth rate of the eigenmode is larger than that of the local analysis at the center. In that case, the eigenfunction has two humps in the regions that are still unstable while the RT mode is completely stabilized at the center in the local analysis.