Acceleration of runaway electrons in solar flares

Journal Article · Thu Mar 01 00:00:00 EST 1990 · Astrophysical Journal; (USA)

DOI:https://doi.org/10.1086/168543· OSTI ID:7041385

Moghaddam-taaheri, E; Goertz, C K ^[1]

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1. Iowa Univ., Iowa City (USA)

The dc electric field acceleration of electrons out of a thermal plasma and the evolution of the runaway tail are studied numerically, using a relativistic quasi-linear code based on the Ritz-Galerkin method and finite elements. A small field-aligned electric field is turned on at a certain time. The resulting distribution function from the runaway process is used to calculate the synchrotron emission during the evolution of the runaway tail. It is found that, during the runaway tail formation, which lasts a few tens of seconds for typical solar flare conditions, the synchrotron emission level is low, almost ot the same order as the emission from the thermal plasma, at the high-frequency end of the spectrum. However, the emission is enhanced explosively in a few microseconds by several orders of magnitude at the time the runaway tail stops growing along the magnetic field and tends toward isotropy due to the pitch-angle scattering of the fast particles. Results indicate that, in order to account for the observed synchrotron emission spectrum of a typical solar flare, the electric field acceleration phase must be accompanied or preceded by a heating phase which yields an enhanced electron temperature of about 2-15 keV in the flare region if the electric field is 0.1-0.2 times the Dreicer field and cyclotron-to-plasma frequency ratios are of order 1-2. 23 refs.

• OSTI ID: 7041385
• Journal Information: Astrophysical Journal; (USA), Vol. 352; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
RUNAWAY ELECTRONS
ACCELERATION
SOLAR FLARES
DIRECT CURRENT
DOPPLER EFFECT
ELECTRIC FIELDS
EMISSION SPECTRA
HOT PLASMA
MAGNETIC FIELDS
NUMERICAL SOLUTION
SOLAR ELECTRONS
SOLAR RADIO BURSTS
SYNCHROTRON RADIATION
BREMSSTRAHLUNG
CURRENTS
ELECTRIC CURRENTS
ELECTROMAGNETIC RADIATION
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
LEPTONS
PLASMA
RADIATIONS
RADIOWAVE RADIATION
SOLAR ACTIVITY
SOLAR PARTICLES
SOLAR RADIATION
SPECTRA
STELLAR RADIATION
640104* - Astrophysics & Cosmology- Solar Phenomena