THE FINITE-AMPLITUDE BEHAVIOR OF THE JOULE MODE UNDER ASTROPHYSICAL CONDITIONS

Magnetized astrophysical plasmas reveal a great deal of structure when spatially resolved. One possible explanation for this structuring is based on the existence of filamenting instabilities driven by radiation. In this paper, we extend previous linear calculations by considering the weakly nonlinear (finite-amplitude) development of such filamenting instabilities in magnetized unstratified plasmas. We show that under most conditions these instabilities (in particular, the Joule mode) are unstable at finite amplitude; in particular, in the temperature and plasma-beta domains characteristic of, for example, much of the solar transition region, these modes - which can be linearly stable under these conditions - become unstable to finite-amplitude perturbations. We discuss how this can be relevant to the problem of heating the solar low transition region by current dissipation.