PARTICLE ACCELERATION PHENOMENA IN ASTROPHYSICAL PLASMASPulsed Acceleration in Solar

We study the nonlinear dynamics of particle acceleration in solar ares by analyzing the time series of various quasi-periodic radio signatures during ares. In particular we present the radio and hard X-ray data of 3 ares which support the following tentative conclusions: 1) Particle acceleration and injection into magnetic loops occurs intrinsically in a pulsed mode (with a typical period of 1-2 s), produced by a single, spatially coherent, nonlinear system (e.g. electric AC eld), rather than by a stochastic system with many spatially independent components (e.g. a \statistical are" produced by a fragmented primary energy release). 2) The nonlinear (quasi-periodic) mode of pulsed particle acceleration and injection into a coronal loop can be stabilized by an MHD wave (oscillation) mode by phase-locking, if both periods are close to each other. 3) Pulsed injection of electron beams into a coronal loop triggers or excites nonlinear relaxational oscillations of wave-particle interactions most likely, when the limit cycle period of the nonlinear wave-particle interaction is close to the mean period of particle injection.