Influence of a Guide Field on the Tearing Mode

The influence of a guide field on the linear and nonlinear dynamics of the tearing mode is examined for a thin current sheet in which the thickness is comparable to a thermal ion gyroradius. The linear Vlasov stability of a Harris sheet with an arbitrary guide field is calculated using a recently developed technique in which the orbit integrals are treated numerically using the exact unperturbed particle orbits and including the global structure of the perturbation inside the integral¹. Both electromagnetic and electrostatic contributions to the field perturbation are included and the eigenvalue problem for the resulting system of integro-differential equations is solved using a finite element representation of the eigenfunction. The addition of a guide field causes the eigenfunction for the tearing instability to be of mixed parity (i.e. a superposition of even and odd parity functions) and strongly alters the quadrupole magnetic field structure in the reconnection region. The influence of the guide field on the mode structure is confirmed using fully kinetic particle-in-cell (PIC) simulations and the resulting reconnection rates in the linear and nonlinear regimes are compared with the growth rates from linear theory for a range of parameters. ¹ W. Daughton, Physics of Plasmas 6, 1329 (1999)