Particle dynamics in a non-flaring solar active region
James Threlfall
University of St Andrews
Ph-A. Bourdin (Austrian Academy of Sciences, Austria) T. Neukirch, C. E. Parnell (University of St Andrews, U.K.)
We present results of test particle orbit calculations based on snapshots of an observationally driven MHD model of a non-flaring slowly-evolving solar active region [detailed in Bourdin et al., A&A 555, A123 (2013)]. The test particle (electron and proton) orbits are calculated using the relativistic guiding centre approximation.
We recover two distinct particle acceleration behaviours which affect both electrons and protons: (i) direct acceleration along field lines and (ii) tangential drifting of guiding centres with respect to local magnetic field. Up to 40% of all particles
actually experience a form of (high energy) particle trap, because of changes in the direction of the electric field and unrelated to the strength of the magnetic field; such particles are included in the first category. Additionally, category (i) electron and proton orbits undergo surprisingly strong acceleration to non-thermal energies (42 MeV), because of the strength and extent of super-Dreicer electric fields created by the MHD simulation. We will discuss how reducing the electric field strength of the MHD model does not significantly affect the efficiency of the (electric field-based) trapping mechanism but does reduce the peak energies gained by orbits.