PARTICLE-ACCELERATION IN LOWER-HYBRID CAVITONS

In this paper we investigate particle acceleration resulting from the relaxation of unstable ion ring distributions, producing strong wave a ctivity at the lower hybrid frequency. It is shown that strong lower h ybrid wave turbulence collapses in configuration space producing densi ty cavities containing intense electrostatic lower hybrid wave activit y. The collapse of these intense nonlinear wavepackets saturate by par ticle acceleration producing energetic electron and ion tails. There a re several mechanisms whereby unstable ion distributions could be form ed in plasmas, including reflection at perpendicular shocks, tearing m odes, and loss cone depletion. Numerical simulations of ion ring relax ation processes, obtained using a 2 1/2-D fully electromagnetic, relat ivistic particle in cell code are discussed. We apply the results to t he problem of explaining energetic particle production in solar flares . The results show the simultaneous acceleration of both electrons and ions to very high energies: electrons are accelerated to energies in the range 10-500 keV, while ions are accelerated to energies of the or der of MeV's. Our simulations also show wave generation at the electro n cyclotron frequency. The strong turbulence collapse process leads to a highly filamented plasma producing many localized regions for parti cle acceleration of width similar or equal to 10 lambda(De).