First-order finite-Larmor-radius effects on magnetic tearing in pinch configurations

The linear and nonlinear evolution of a single-helicity tearing mode in a cylindrical, force-free pinch are investigated using a fluid model with first-order finite-Larmor-radius corrections. Linear results computed with the NIMROD [nonideal magnetohydrodynamics (MHD) with rotation, open discussion] code [Sovinec et al., J. Comput. Phys. 195, 355 (2004)] produce a regime at small rho(s) where the growth rate is reduced relative to resistive MHD, though the Hall term is not significant. The leading order contributions from ion gyroviscosity may be expressed as a drift associated with del B-0 and poloidal curvature for experimentally relevant beta = 0.1, S similar to 10(5) - 10(6) force-free equilibria. The heuristic analytical dispersion relation, gamma(4)(gamma - i omega(*gv)) = gamma(5)(MHD) where omega(*gv) is the gyroviscous drift frequency, confirms numerical results. The behavior of our cylindrical computations at large rho(s) corroborates previous analytic slab studies where an enhanced growth rate and radially localized Hall dynamo are predicted. Similar to previous drift-tearing results, nonlinear computations with cold ions demonstrate that the Hall dynamo is small when the island width is large in comparison with the scale for electron-ion coupling. The saturation is then determined by the resistive MHD physics. However, with warm ions the gyroviscous stress supplements the nonlinear Lorentz force, and the saturated island width is reduced. VC 2011 American Institute of Physics. [doi:10.1063/1.3571599]