Asymmetric tearing mode in the presence of viscosity

The linear stability of the tearing mode (TM) in a plasma column is investigated in the presence of viscosity and finite equilibrium current density gradients (i.e., asymmetries). It is shown that for low beta, both effects are essential in order to properly describe the mode behaviour close to marginality. In particular, the theory introduces a critical threshold for the destabilization, such that the perturbation grows only if Delta'>Delta'(cr). The value of Delta'(cr) depends on the equilibrium configuration and on the plasma parameters. Most importantly, Delta'(cr) can take negative values, thus allowing unstable tearing modes for Delta' < 0 (even in the absence of bootstrap current). [doi:10.1063/1.3660410]