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Fast Solar Flare Proton Acceleration by MHD Turbulence

Published online by Cambridge University Press:  19 July 2016

Dean. F. Smith
Dean. F. Smith*
Affiliation:
Berkeley Research Associates and Department of Astrophysical, Planetary, and Atmospheric Sciences University of Colorado, Boulder Boulder, Colorado 80309

Abstract

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Proton acceleration by short-wavelength Alfven (A) waves resonant at the first harmonic of the proton gyrofrequency is reconsidered, taking into account nonlinear wave-wave interactions, collisionless wave losses, and wave escape losses in the geometry of a model coronal loop. It is shown that for the A wave levels required for acceleration in the transrelativistic regime in the 1982 June 3 flare and for acceleration in the nonrelativistic regime in the 1980 June 7 flare, the nonlinear wave interaction of scattering on the polarization clouds of ions will be important. This interaction rapidly isotropizes the A waves which divide their energy with fast magnetosonic (M) waves with a negligible change in their frequency spectrum. Because of electron Landau damping and escape losses, the M waves are confined to two narrow cones about the magnetic field and the total (A+M) wave distribution is still highly anisotropic. The total (A+M) wave spectrum has the same acceleration efficiency as a pure A wave spectrum. There are two principal problems with models of this type. The first is that a large wave energy density is required in a fairly narrow range in k-space. The second is that the protons are effectively bottled up. This makes very impulsive behavior as in the 7 June 1980 flare difficult to explain because proton precipitation is relatively slow.

Type
VIII. Solar Flares
Information
Symposium - International Astronomical Union , Volume 142: Basic Plasma Processes on the Sun , 1990 , pp. 375 - 382
Copyright
Copyright © Kluwer 1990 

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