Energetic Ion Acceleration by Small-scale Solar Wind Flux Ropes

[摘要] We consider different limits of our recently developed kinetic transport theory to investigate the potential of supersonic solar wind regions containing several small-scale flux ropes to explain the acceleration of suprathermal ions to power-law spectra as observations show. Particle acceleration is modeled in response to flux-rope activity involving contraction, merging (reconnection), and collisions in the limit where the particle gyoradius is smaller than the characteristic flux-rope scale length. The emphasis is mainly on the statistical variance in the electric fields induced by flux-rope dynamics rather than on the mean electric field induced by multiple flux ropes whose acceleration effects are discussed elsewhere. Our steady-state analytical solutions suggest that ion drift acceleration by flux ropes, irrespective of whether displaying incompressible or compressible behavior, can yield power laws asymptotically at higher energies whereas an exponential spectral rollover results asymptotically when field-aligned guiding center motion acceleration occur by reconnection electric fields from merging flux ropes. This implies that at sufficiently high particle energies, drift acceleration might dominate. We also expect compressive flux ropes to yield harder power-law spectra than incompressible flux ropes.

[发布机构] Dept. of Space Science, University of Alabama in Huntsville, Huntsville, United States^1;Center for Space Plasma and Aeronomic Reseach, University of Alabama in Huntsville, Huntsville, United States^2;Heliophysical Laboratory, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation RAS (IZMIRAN), Troitsk, Moscow, Russia^3

[效力级别] 天文学 [学科分类] 天文学(综合)

[关键词] Acceleration effects;Electric field induced;Energetic ion acceleration;Guiding centers;Kinetic transport;Particle acceleration;Particle energy;Statistical variance