Saturation of a tearing mode in zero-β full magnetohydrodynamics

Within the cylindrical approximation, the nonlinear saturation of a tearing mode island in the full magnetohydrodynamics (MHD) model with no pressure and a uniform resistivity profile is described using a recent perturbation method based on the technique of matched asymptotic expansion, where the perturbation parameter is the island width w(s). The matching condition provides the saturation equation for w(s) that is given to the adequate order and does not depend on the normalization length. This enables to prove that the errors due to reduced MHD (RMHD) are negligible in the calculation of tearing mode saturation in the tokamak. It also provides a way to benchmark MHD numerical simulations of magnetic self-reversal for the reversed-field pinch where RMHD does not apply. (c) 2007 American Institute of Physics.