Numerical studies of particle acceleration at turbulent, oblique shocks with an application to prompt ion acceleration during solar flares

Details Numerical studies of particle acceleration at turbulent, oblique shocks with an application to prompt ion acceleration during solar flares Numerical studies of particle acceleration at turbulent, oblique shocks with an application to prompt ion acceleration during solar flares

Jul 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986apj...306..710d&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 306, July 15, 1986, p. 710-729.

Statistics

Computation

86

Magnetohydrodynamic Turbulence, Oblique Shock Waves, Particle Acceleration, Solar Flares, Computational Astrophysics, Energy Spectra, Power Spectra, Solar Protons

Scientific paper

In this paper we address the problem of charged particle acceleration at oblique, fast-mode collisionless MHD shock waves when magnetic turbulence exists in the regions upstream and downstream of the shock. Specifically, we consider how the acceleration rate depends upon the angle θ1 between the shock normal and the mean upstream magnetic field. To handle the general situation where θ1, the turbulence level, the shock strength, and the energy of injected particles can assume a range of values, we perform fully relativistic, test particle simulations that involve integrating along particle phase space orbits in the shock turbulence system. As an application of the numerical code, we study proton acceleration at shocks under conditions appropriate to the lower solar corona to simulate prompt ion acceleration during solar flares. Particles undergo shock acceleration through a combination of the shock drift and first-order Fermi processes. For protons injected at 100 keV and left in the system for 500 gyroperiods (˜ 7 ms in a 50 G magnetic field) we obtain the following results: (1) the percentage of protons accelerated above 10 MeV within 7 ms increases with increasing θ1, from 0% at θ1 = 0° to a maximum of 9% at θ1= 60° (2) the case θ1 = 75° produces the largest, most rapid energy gains, with ˜1% of the protons accelerated above 50 MeV; (3) for 45° < θ1 < 75° , a separate proton population with energies between 100 keV and 10 MeV is produced during a superfast acceleration phase lasting only ˜ 10 gyroperiods (˜ 100 μs) after injection; (4) we compare the peak energy reached at O = 0 and energy spectrum produced at θ1 = 75° with predictions from theoretical models, and find reasonable agreement, although discrepancies do exist. We discuss the implications of the numerical results as they pertain to time constraints and collisional loss processes during shock acceleration in the solar corona.

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