Wednesday, March 20, 2013

1303.4334 (Markus Battarbee et al.)

Acceleration of Energetic Particles Through Self-Generated Waves in a Decelerating Coronal Shock    [PDF]

Markus Battarbee, Timo Laitinen, Rami Vainio, Neus Agueda
We have developed a simulation model of particle acceleration in coronal shock waves. The model is based on a Monte Carlo method, where particles are traced in prescribed large-scale electromagnetic fields utilizing the guiding center approximation. The particles are scattered in the turbulence according to quasilinear theory, with the scattering amplitude directly proportional to the intensity of Alfv\'en waves at gyro-resonant wavenumbers. The Alfv\'en waves are traced simultaneously with the particles, so that the wave field is propagated outwards from the Sun using WKB propagation supplemented with a phenomenological wavenumber diffusion term and a growth rate computed from the net flux of the accelerated particles. We consider initial wave amplitudes small enough to allow rapid escape of particles from the shock to the ambient medium. Thus, in our model the Alfv\'en waves responsible for the diffusive acceleration of particles are generated by the accelerated particles themselves. In this work, we study the effects of non-constant shock velocity and non-monotonic Alfv\'en velocity on particle acceleration scenarios. We report in particular how the deceleration of a shock affects particle intensity and turbulence power evolution in the vicinity of the shock.
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