Instability of a magnetized plasma jet

The stability characteristics of a plasma jet V(x) = sech(2) x embedded in a parallel magnetic field B(x) = B-0 tanh x are investigated. The Kelvin-Helmholtz kink mode, which dominates at small Bo, is stabilized at B-0 = 0.46, while the pinch mode remains unstable up to B-0 = 0.96. Contrary to a nonmagnetized jet, for finite Bo the kink mode saturates quasilinearly by broadening the jet, such that B-0/V-max becomes larger than the marginal value 0.46. Including finite resistivity the nonlinear behavior is eventually governed by the tearing mode for all values of B-0 not equal 0, consisting of a single plasmoid moving along the jet. Hence the shear flow cannot stabilize the tearing mode, so that the apparent tearing stability of resistive current sheets observed in numerical simulations of magnetic reconnection is only due to finite-length effects. (C) 1998 American Institute of Physics. [S1070-664X(98)01207-5]