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Дата изменения: Wed Apr 18 17:25:48 2012 Дата индексирования: Tue Oct 2 06:39:50 2012 Кодировка: Windows-1251 Поисковые слова: spacecraft |
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"Stochastic
Particle Acceleration and the Problem of Background Plasma Overheating" D.O. Chernyshov and
V.A. Dogiel (P.N.Lebedev Institute of
Physics) Abstract: The origin of hard X-ray (HXR)
excess emission from clusters of galaxies is still an enigma, whose nature is debated. One of the possible
mechanism to produce this emission is the bremsstrahlung model.
However, previous analytical and numerical calculations showed that in this
case the intracluster plasma had to be overheated very fast because
suprathermal electrons emitting the HXR excess lose their energy mainly by
Coulomb losses, i.e. they heat the background plasma. It was concluded also
from these investigations that it is problematic to produce emitting
electrons from a background plasma by stochastic (Fermi) acceleration because
the energy supplied by external sources in the form of Fermi acceleration is
quickly absorbed by background plasma. In other words the Fermi acceleration
is ineffective for particle acceleration. We revisited this problem and found
that at some parameters of acceleration the rate of plasma heating is rather
low and the acceleration tails of non-thermal particles are generated and
exist for a long time while the plasma temperature is almost constant . We
showed also that for some regimes of acceleration the plasma is cooled down
instead of to be heated up, though external sources (in the form of external
acceleration) supply energy to the system. The reason is that in the last
case the acceleration subtracts effectively high energy particles from the
thermal pool that is the reason of plasma cooling (analogue of Maxwell's
demon). |