Particle-in-cell simulations of lowerhybrid waves generated by an ion-ring velocity distribution

Fully electromagnetic particle-in-cell simulations of the excitation of the lower-hybrid mode in a plasma driven by an ion-ring distribution using the Lsp code are presented. At early times the simulations agree with linear theory. The resulting wave evolution and non-linear plasma and ring-ion heating are compared previous simulation results [1] and with theoretical models [2], [3]. The 2D simulations show that, when the magnetic field is perpendicular to the wave vector, k, a space-charge electric field caused caused by the unstable waves works in conjunction with the applied magnetic field to cause the perturbed magnetic flux to wrap up into circular paramagnetic vortices in which electrons E ×B drift around a positively charged center. These vortices are similar to those observed in 2D simulations of magnetic-field penetration into a spatially inhomogeneous plasma [4]. These vortices are altered by the addition of a small, in-plane, component of magnetic field which allows electrons to stream along field lines effectively shorting out one component of the electric field. In this case, the vortex structures are no longer circular but elongated along the direction of the in-plane magnetic field component.