Particle acceleration by lower-hybrid turbulence

Abstract

We investigate particle acceleration by strong lower-hybrid turbulence produced by the relaxation of an energetic perpendicular ion ring distribution. Ion ring distributions are associated with counterstreaming plasma flows in a magnetic field, and are found at perpendicular shocks as a result of ion reflection from the shock surface. Using a 2½D particle-in-cell (PIC) code that is fully electromagnetic and relativistic, we show that the ion ring is unstable to the generation of strong plasma turbulence at the lower-hybrid resonant frequency. The lower-hybrid wave turbulence collapses in configuration space, producing density cavities. The collapse of the cavities is halted by particle acceleration, producing energetic electron and ion tails. For solar flare plasmas with temperatures of 1 keV and a ratio of the plasma frequency to the electron cyclotron frequency of ½, we demonstrate electron acceleration to energies up to MeV, while the ions are accelerated to energies in the region of several MeV.