Particle Acceleration and Intermittent Turbulence in Coronal Loops

Abstract

A test particle numerical experiment is performed to simulate particle acceleration in low-frequency turbulence generated by footpoint motions in a coronal loop. The turbulence is modeled within the reduced MHD theory. Only the effect of the resistive electric field E|| is retained, which is mainly parallel to the axial magnetic field. In its spectrum, the contribution of small scales is dominant. The spatial structure of E|| is obtained by a synthetic turbulence method (p-model), which allows us to reproduce intermittency. By solving the relativistic motion equations, the time evolution of particle distribution is calculated. Electrons can be accelerated to energies of the order of 50 keV in less than 0.3 s, and the final energy distribution can exhibit a power-law range. A correlation is found between the heating events in the MHD turbulence and particle acceleration that is qualitatively similar to what is observed in solar flares. Spatial intermittency plays a key role in acceleration, enhancing both the extension of a power-law range and the maximum energy.