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Diffusive Shock Acceleration and Reconnection Acceleration Processes

Zank, G. P. and Hunana, P. and Mostafavi, P. and Le Roux, J. A. and Li, Gang and Webb, G. M. and Khabarova, O. and Cummings, A. and Stone, E. and Decker, R. (2015) Diffusive Shock Acceleration and Reconnection Acceleration Processes. Astrophysical Journal, 814 (2). Art. No. 137. ISSN 0004-637X. doi:10.1088/0004-637X/814/2/137.

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Shock waves, as shown by simulations and observations, can generate high levels of downstream vortical turbulence, including magnetic islands. We consider a combination of diffusive shock acceleration (DSA) and downstream magnetic-island-reconnection-related processes as an energization mechanism for charged particles. Observations of electron and ion distributions downstream of interplanetary shocks and the heliospheric termination shock (HTS) are frequently inconsistent with the predictions of classical DSA. We utilize a recently developed transport theory for charged particles propagating diffusively in a turbulent region filled with contracting and reconnecting plasmoids and small-scale current sheets. Particle energization associated with the anti-reconnection electric field, a consequence of magnetic island merging, and magnetic island contraction, are considered. For the former only, we find that (i) the spectrum is a hard power law in particle speed, and (ii) the downstream solution is constant. For downstream plasmoid contraction only, (i) the accelerated spectrum is a hard power law in particle speed; (ii) the particle intensity for a given energy peaks downstream of the shock, and the distance to the peak location increases with increasing particle energy, and (iii) the particle intensity amplification for a particular particle energy, f(x,c/c_0)/f(0,c/c_0), is not 1, as predicted by DSA, but increases with increasing particle energy. The general solution combines both the reconnection-induced electric field and plasmoid contraction. The observed energetic particle intensity profile observed by Voyager 2 downstream of the HTS appears to support a particle acceleration mechanism that combines both DSA and magnetic-island-reconnection-related processes.

Item Type:Article
Related URLs:
URLURL TypeDescription
Zank, G. P.0000-0002-4642-6192
Li, Gang0000-0001-9313-251X
Cummings, A.0000-0002-3840-7696
Additional Information:© 2015 American Astronomical Society. Received 2015 August 28; accepted 2015 October 14; published 2015 November 30. We acknowledge the partial support of NASA grants NNX08AJ33G, Subaward 37102-2, NNX09AG70G, NNX09AG63G, NNX09AJ79G, NNG05EC85C, Subcontract A991132BT, NNX09AP74A, NNX10AE46G, NNX09AW45G, NNX14AF43G, NNN12AA012, NNX15AI65G, and NSF grant ATM-0904007. O.K. was supported by RFBR grant no. 14-02- 00769. G.P.Z. thanks R. Bruno for his kind hospitality while visiting the INAF.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Russian Foundation for Basic Research (RFBR)14-02- 00769
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Subject Keywords: acceleration of particles; magnetic reconnection; shock waves; turbulence
Issue or Number:2
Record Number:CaltechAUTHORS:20160324-112710122
Persistent URL:
Official Citation:G. P. Zank et al 2015 ApJ 814 137
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:65659
Deposited On:25 Mar 2016 02:37
Last Modified:10 Nov 2021 23:48

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