On the relaxation toward Kappa-Distribution Accelerated Electron Populations in Solar Flares
Abstract
Driven by recent RHESSI observations of confined loop-top hard X-ray sources in solar flares, we consider stochastic acceleration of electrons in the presence of Coulomb collisions. It is shown that when the diffusive acceleration time scales as the collisonal friction time then the electron distribution function relaxes toward a kappa distribution. We also show that the evolution toward this kappa distribution involves a "wave front" propagating forwards in velocity space so that electrons of higher energy are accelerated later. While the relaxation toward a Maxwellian distribution is well known to imply spatially diffusive transport, it is shown that relaxation toward this kappa distribution is likely to involve anomalous (fractional) diffusion of the particles in the acceleration region.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMSH13D..04B
- Keywords:
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- 4468 Probability distributions;
- heavy and fat-tailed;
- NONLINEAR GEOPHYSICSDE: 7827 Kinetic and MHD theory;
- SPACE PLASMA PHYSICSDE: 7845 Particle acceleration;
- SPACE PLASMA PHYSICSDE: 7851 Shock waves;
- SPACE PLASMA PHYSICS