Abstract and subjects
Magnetic flux ropes (or magnetic islands) are ubiquitous space plasma structures. Recent observations suggest that they are often associated with the acceleration of charged particles, but detailed acceleration mechanisms remain unclear. In this study, we present PIC simulations studying particle acceleration due to magnetic flux ropes. We consider a simple 2D configuration of two-magnetic-island coalescence. Some electrons and protons are found to be accelerated to more than 10 times their initial kinetic energies at the end of the simulation. We use a particle tracing technique on the high-energy particles to clarify the associated acceleration mechanisms. We find that reconnection electric field and Fermi-type acceleration due to magnetic island contraction can explain the particle energy gain, which is consistent with previous simulation studies. Our results also suggest that electrons are more responsive to the island contraction mechanism compared to ions. An effective island contraction rate is derived from the simulation data. Finally we briefly discuss a statistical description of particle acceleration associated with interacting magnetic flux ropes, and how it can be connected to simulations.