PULSED ACCELERATION IN SOLAR-FLARES

We study the nonlinear dynamics of particle acceleration in solar flares by analyzing the time series of various quasi-periodic radio signatures during flares. In particular we present the radio and hard X-ray data of three flares which support the following tentative conclusions: 1. Particle acceleration and injection into magnetic structures occurs intrinsically in a pulsed mode (with a typical period of 1-2s), produced by a single, spatially coherent, nonlinear system, rather than by a stochastic system with many spatially independent components (''statistical flare'' 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 phase locking with an MI-ID wave (oscillation) mode, if both periods are close to each other. 3. Pulsed injection of electron beams into a coronal loop may trigger nonlinear relaxational oscillations of wave-particle interactions. This is particularly likely when the limit cycles of both systems are similar.