PARTICLE-ACCELERATION IN DYNAMICAL COLLISIONLESS RECONNECTION

We describe the characteristics of particle orbits in the presence of an MHD disturbance in a medium with a magnetic field containing an X-t ype neutral point. The scalar resistivity of the medium is assumed to be a parameter of the problem. We calculate the evolution of particles in the presence of the same MHD disturbance. Initially, the particles are uniformly distributed in space and have a Maxwellian Velocity dis tribution. The resulting particle distributions depend on the value of the scalar resistivity. We attempt to match the MHD description with our test particle description by adjusting the value of the scalar res istivity until the particles gain energy at the same rate that the wav e loses it. In practice, such matching is not achieved for reasons tha t throw light on the limitations of a MHD description with scalar resi stivity. Irrespective of difficulties in defining the 'correct' value of the resistivity, we have demonstrated that the passage of such a re connective disturbance may accelerate protons to gamma-ray producing e nergies, or at least to energies where they could play a role in energ y transport. The fraction of high energy protons depends on the ambien t density, with the highest-energy particles being produced when the a mbient density is smallest.