SUBTHRESHOLD STOCHASTIC DIFFUSION WITH APPLICATION TO SELECTIVE ACCELERATION OF HE-3 IN SOLAR-FLARES

A mechanism of resonant acceleration driven by waves below the threshold for global chaos is discussed. It affects only resonant ions and proceeds through a stochastic network in phase space (Arnold web) characterizing this particular type of wave-particle interaction. A theory for selective acceleration of He-3 and He-3-like ions through resonant subthreshold diffusion is proposed. It relies on the coincidence of two natural resonances, the two-ion (He-4, H) hybrid plasma resonance with the ion cyclotron resonance of He-3. This occurs over a wide range of plasma parameters for relative abundances He-4/H congruent-to 0.25. It is argued that existing low-frequency fluctuations or high-frequency noise tends to amplify the selective diffusion of He-3.