Hyperresistivity due to viscous tearing mode turbulence

The quasilinear hyperresistivity coefficient DH for flattening a current profile in resistive magnetohydrodynamics is computed. It is found that DH is independent of Δ', the constant-ψ matching parameter, for viscous tearing modes. This is in contrast to the situation for inertial tearing modes, for which DH scales as Δ'-1/5. It is reasonable to consider viscous rather than inertial tearing modes for computing DH because inertial tearing modes cross over to the viscous regime near quasilinear saturation, when their growth rates are sufficiently small. This quasilinear calculation of hyperresistivity related to a spectrum of tearing modes invokes the assumption that the tearing layers overlap. This is in contrast to the usual assumption of overlap of magnetic islands, i.e., magnetic field line chaos