Particle acceleration during the coalescence of two magnetic loops in electron-ion plasmas

Abstract

Electron and ion acceleration mechanisms during the coalescence process of two adjacent magnetic loops through cohelicity and counterhelicity magnetic reconnection are investigated by using a two-dimensional, electromagnetic, and relativistic particle-in-cell (PIC) simulation. Three types of acceleration mechanisms are found by the PIC simulations. (1) Electrons in a current sheet generated between two adjacent magnetic loops are accelerated by the electric field induced during the collisionless magnetic reconnection, and their energy spectrum is characterized by the power law. (2) Ions trapped in the front of fast magnetosonic shock waves generated during the coalescence process are promptly accelerated by the surfatron acceleration mechanism. (3) During the coalescence process through counterhelicity magnetic reconnection, ions outside the current sheet are accelerated by E×B drift, where the electrostatic fields E perpendicular to local magnetic field are generated by the collision between surrounding magnetic field barrier and electron-dominated jet from the current sheet. During the coalescence process through cohelicity magnetic reconnection, the electron energy spectrum in the current sheet is characterized by the power law whose index is about 5, while during the coalescence process through counterhelicity magnetic reconnection, the electron energy spectrum is characterized by the double power law whose indices are about 3.3 and 6. The simulation results obtained here are applied to the proton and electron acceleration during solar flares. The maximum energy of accelerated electrons reaches about 100 keV, while the maximum energy of accelerated protons by the surfatron acceleration mechanism is about 10 MeV for both cohelicity and counterhelicity case.