A Classification Scheme For Turbulent Acceleration Processes In Solar Flares

TL;DR

This paper develops a comprehensive classification scheme for stochastic acceleration mechanisms in solar flares, considering electromagnetic field properties and particle transport, and provides formulas for diffusion coefficients and acceleration times for observational comparison.

Contribution

It introduces a new classification framework for turbulent acceleration processes in solar flares, incorporating different particle transport regimes and deriving relevant diffusion and acceleration time expressions.

Findings

Classified acceleration processes as resonant, non-resonant, or resonant-broadened.

Derived expressions for momentum-dependent diffusion coefficients.

Calculated energy-dependent acceleration times for observational comparison.

Abstract

We establish a classification scheme for stochastic acceleration models involving low-frequency plasma turbulence in a strongly magnetized plasma. This classification takes into account both the properties of the accelerating electromagnetic field, and the nature of the transport of charged particles in the acceleration region. We group the acceleration processes as either resonant, non-resonant or resonant-broadened, depending on whether the particle motion is free-streaming along the magnetic field, diffusive or a combination of the two. Stochastic acceleration by moving magnetic mirrors and adiabatic compressions are addressed as illustrative examples. We obtain expressions for the momentum-dependent diffusion coefficient $D(p)$, both for general forms of the accelerating force and for the situation when the electromagnetic force is wave-like, with a specified dispersion relation $\omega=\omega(k)$. Finally, for models considered, we calculate the energy-dependent acceleration time, a quantity that can be directly compared with observations of the time profile of the radiation field produced by the accelerated particles, such as during solar flares.