The evolution of energetic particles and the emitted radiation in solar flares

Miscellaneous · Sun Jan 01 00:00:00 EST 1989

OSTI ID:6597594

Lu, E T

The evolution of accelerated particle distributions in a magnetized plasma and the resulting radiation are calculated, and the results are applied to solar flares. To study the radiation on timescales of order of the particle lifetimes, the evolution of the particle distribution is determined using the Fokker-Planck equation including Coulomb collisions and magnetic mirroring. Analytic solution to the equation are obtained for limiting cases such as homogeneous injection in a homogeneous plasma, and for small pitch angle. These analytic solutions are used to place constraints on flare parameters such as density, loop length, and the injection timescale for very short impulsive flares. For general particle distributions in arbitrary magnetic field and background density, the equation is solved numerically. Over longer timescales, the variation with X-ray peak fluxes is shown to be consistent with the nonthermal thick target beam model, while multithermal and thin target models have difficulty matching the observations. The relative timing of microwaves and X-ray during individual flares is then investigated. The observation that the microwaves are observed to peak {approximately}2 s later than hard X-rays is interpreted as being due to an excess of microwave flux above that predicted by the simple thick target model. The author discusses a number of possible sources for this excess microwave flux including a flattening in the electron spectrum above hard X-ray energies, thermal synchroton emission, and trapping of electrons by converging magnetic field.

• Research Organization: Stanford Univ., CA (USA)
• OSTI ID: 6597594
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
SOLAR FLARES
SOLAR RADIATION
ACCELERATION
ANALYTICAL SOLUTION
DENSITY
HARD X RADIATION
HOMOGENEOUS PLASMA
MAGNETIC FIELDS
MICROWAVE RADIATION
NUMERICAL SOLUTION
SYNCHROTRON RADIATION
TRAPPING
VARIATIONS
X-RAY SPECTRA
BREMSSTRAHLUNG
ELECTROMAGNETIC RADIATION
IONIZING RADIATIONS
PHYSICAL PROPERTIES
PLASMA
RADIATIONS
SOLAR ACTIVITY
SPECTRA
STELLAR RADIATION
X RADIATION
640104* - Astrophysics & Cosmology- Solar Phenomena