Particle acceleration by combined diffusive shock acceleration and downstream multiple magnetic island acceleration

14th Annual International Astrophysics Conference: Linear and Nonlinear Particle Energization throughout the Heliosphere and Beyond

物理学;天文学

Zank, G.P.^1,2 ; Hunana, P.^1 ; Mostafavi, P.^1,2 ; Le Roux, J.A.^1,2 ; Li, Gang^1,2 ; Webb, G.M.^1 ; Khabarova, O.^3

Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville

AL

35805, United States^1

Department of Space Science, University of Alabama in Huntsville, Huntsville

AL

35805, United States^2

Heliophysical Laboratory, Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation RAS (IZMIRAN), Troitsk, Moscow

142190, Russia^3

关键词: Accelerated particles;    Charged particle acceleration;    Diffusive shock accelerations;    Induced electric fields;    Intensity amplification;    Interplanetary shocks;    Particle acceleration;    Upstream turbulence;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/642/1/012031/pdf
DOI  :  10.1088/1742-6596/642/1/012031

学科分类：天文学(综合)

来源: IOP

【 摘 要 】

As a consequence of the evolutionary conditions [28; 29], shock waves can generate high levels of downstream vortical turbulence. Simulations [32-34] and observations [30; 31] support the idea that downstream magnetic islands (also called plasmoids or flux ropes) result from the interaction of shocks with upstream turbulence. Zank et al. [18] speculated that a combination of diffusive shock acceleration (DSA) and downstream reconnection-related effects associated with the dynamical evolution of a "sea of magnetic islands" would result in the energization of charged particles. Here, we utilize the transport theory [18; 19] for charged particles propagating diffusively in a turbulent region filled with contracting and reconnecting plasmoids and small-scale current sheets to investigate a combined DSA and downstream multiple magnetic island charged particle acceleration mechanism. We consider separately the effects of the anti-reconnection electric field that is a consequence of magnetic island merging [17], and magnetic island contraction [14]. For the merging plasmoid reconnection- induced electric field only, we find i) that the particle spectrum is a power law in particle speed, flatter than that derived from conventional DSA theory, and ii) that the solution is constant downstream of the shock. For downstream plasmoid contraction only, we find that i) the accelerated particle spectrum is a power law in particle speed, flatter than that derived from conventional DSA theory; ii) for a given energy, the particle intensity peaks downstream of the shock, and the peak location occurs further downstream of the shock with increasing particle energy, and iii) the particle intensity amplification for a particular particle energy, f(x, c/c0)/f(0, c/c0), is not 1, as predicted by DSA theory, but increases with increasing particle energy. These predictions can be tested against observations of electrons and ions accelerated at interplanetary shocks and the heliospheric termination shock.