Turbulence, Magnetic Reconnection in Turbulent Fluids and Energetic Particle Acceleration

Type Journal Article
Names A. Lazarian, L. Vlahos, G. Kowal, H. Yan, A. Beresnyak, E. M. de Gouveia Dal Pino
Publication Space Science Reviews
Volume 173
Pages 557-622
Journal Abbreviation Space Science Reviews
Date November 1, 2012
DOI 10.1007/s11214-012-9936-7;
ISSN 0038-6308
URL http://adsabs.harvard.edu/abs/2012SSRv..173..557L
Library Catalog NASA ADS
Abstract Turbulence is ubiquitous in astrophysics. It radically changes many astrophysical phenomena, in particular, the propagation and acceleration of cosmic rays. We present the modern understanding of compressible magnetohydrodynamic (MHD) turbulence, in particular its decomposition into Alfvén, slow and fast modes, discuss the density structure of turbulent subsonic and supersonic media, as well as other relevant regimes of astrophysical turbulence. All this information is essential for understanding the energetic particle acceleration that we discuss further in the review. For instance, we show how fast and slow modes accelerate energetic particles through the second order Fermi acceleration, while density fluctuations generate magnetic fields in pre-shock regions enabling the first order Fermi acceleration of high energy cosmic rays. Very importantly, however, the first order Fermi cosmic ray acceleration is also possible in sites of magnetic reconnection. In the presence of turbulence this reconnection gets fast and we present numerical evidence supporting the predictions of the Lazarian and Vishniac (Astrophys. J. 517:700-718, 1999) model of fast reconnection. The efficiency of this process suggests that magnetic reconnection can release substantial amounts of energy in short periods of time. As the particle tracing numerical simulations show that the particles can be efficiently accelerated during the reconnection, we argue that the process of magnetic reconnection may be much more important for particle acceleration than it is currently accepted. In particular, we discuss the acceleration arising from reconnection as a possible origin of the anomalous cosmic rays measured by Voyagers as well as the origin cosmic ray excess in the direction of Heliotail.
Tags COSMIC RAYS, Magnetic reconnection, acceleration, turbulence
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