Particle Simulation of a Collision between a Plasma Cloud and a Current Loop

Abstract

We present a model of a collision between a plasma cloud and a current loop by performing simulations with a three-dimensional electromagnetic particle code. The loop heating and particle acceleration in such collision processes are crucially important in understanding the triggering mechanisms of solar flares. Theories and observations previously studied have revealed that plasmoids produced in the coalescence process of current loops escape from the interaction region. Furthermore, they may move to another magnetic loop, colliding with it and triggering a flare. Based on this idea, we investigate this simulation study as a flare model. A cloud is pushed across an ambient magnetic field to a current loop along the field. Simulation results show that a great deal of the released energy from the cloud is transferred into loop kinetic energy, resulting in heating of the loop. If the initial kinetic energy of the cloud is large enough to compress and bend the ambient magnetic field distinctly, nonthermal electrons are produced in the loop, which have a broken power law spectrum. Those heated electrons are responsible for soft X-ray and hard X-ray emissions from the loop. In addition, electrons in the cloud are also heated. The high-energy electrons in the loop and the cloud are almost identical, with the same maximum energies, of the order of 30 times the thermal energy. The high-energy electrons in the cloud correspond to a hard X-ray source above the loop apex.