Abstract:
Much of nonthermal, high-energy particles has been observed in the
solar-terrestrial environment as well as in the astrophysical
phenomena,and their energy density is known to be comparable to the
energy density of the magnetic field and the thermal energy density of
gas.  The source of the high-energy particles and the acceleration
mechanism are an important unresolved issue in the Universe.  After the
idea of the stochastic acceleration by Enrico Fermi in 1949, many
acceleration models have been proposed, and the diffusive shock
acceleration is believed to be primary mechanism by which particles gain
nonthermal energies through stochastic scattering between the shock
upstream and downstream.  However, recent modern observations suggest
that the diffusive shock acceleration alone cannot explain the observed
cosmic ray particles, and other acceleration mechanisms with much
efficient production of nonthermal particle are now extensively
investigated.
A review of our recent progress of particle acceleration mechanism is
given by paying a special attention to collisionless plasma processes in
shock wave, magnetic reconnection, and accretion disk etc.