Preferential Heating and Acceleration of Heavy Ions in Impulsive Solar Flares

We simulate decaying turbulence in a homogeneous pair plasma using a three-dimensional electromagnetic particle-in-cell method. A uniform background magnetic field permeates the plasma such that the magnetic pressure is three times larger than the thermal pressure and the turbulence is generated by counter-propagating shear Alfvén waves. The energy predominately cascades transverse to the background magnetic field, rendering the turbulence anisotropic at smaller scales. We simultaneously move several ion species of varying charge to mass ratios in our simulation and show that the particles of smaller charge to mass ratios are heated and accelerated to non-thermal energies at a faster rate. This is in accordance with the enhancement of heavy ions and a non-thermal tail in their energy spectrum observed in the impulsive solar flares. We further show that the heavy ions are energized mostly in the direction perpendicular to the background magnetic field, with a rate consistent with our analytical estimate of the rate of heating due to cyclotron resonance with the Alfvén waves, of which a large fraction is due to obliquely propagating waves.