Heating and acceleration at X-point reconnection

We have performed numerical simulations of the non-relativistic particle motion in the external static magnetic and electric fields of an X-point configuration. The properties of both the perpendicular and the parallel invariants have been examined and the size of the region where the adiabatic properties of the particle motion are violated is estimated. The change of the longitudinal invariant due to the crossing of the separatrices has also been evaluated. In the non-adiabatic region, particle trajectories have been found which exhibit chaotic behaviour: we have used symplectic integration and observed a positive value of the maximum Lyapunov exponent and a fractional value of the correlation dimension (similar or equal to 2.5). The population dynamics of a thousand particles has also been investigated. The study of the velocity distributions indicate that particle acceleration is mainly perpendicular to the magnetic field, leading to the development of a large anisotropy in the distribution function.