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A Stringent Limit on the Amplitude of Alfvénic Perturbations in High-beta Low-collisionality Plasmas

Squire, J. and Quataert, E. and Schekochihin, A. A. (2016) A Stringent Limit on the Amplitude of Alfvénic Perturbations in High-beta Low-collisionality Plasmas. Astrophysical Journal, 830 (2). Art. No. L25. ISSN 0004-637X. doi:10.3847/2041-8205/830/2/L25.

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It is shown that low-collisionality plasmas cannot support linearly polarized shear-Alfvén fluctuations above a critical amplitude δ β_⊥/β_0 ~ β^(-1/2), where β is the ratio of thermal to magnetic pressure. Above this cutoff, a developing fluctuation will generate a pressure anisotropy that is sufficient to destabilize itself through the parallel firehose instability. This causes the wave frequency to approach zero, interrupting the fluctuation before any oscillation. The magnetic field lines rapidly relax into a sequence of angular zig-zag structures. Such a restrictive bound on shear-Alfvén-wave amplitudes has far-reaching implications for the physics of magnetized turbulence in the high-β conditions prevalent in many astrophysical plasmas, as well as for the solar wind at ~1 au where β ≳ 1.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Squire, J.0000-0001-8479-962X
Quataert, E.0000-0001-9185-5044
Schekochihin, A. A.0000-0003-4421-1128
Alternate Title:Finite-amplitude shear-Alfvén waves do not propagate in weakly magnetized collisionless plasmas
Additional Information:© 2016. The American Astronomical Society. Received 2016 August 16; revised 2016 September 15; accepted 2016 September 16; published 2016 October 12. It is a pleasure to thank S. Bale, C. H. K. Chen, S. Cowley, M. Kunz, and M. Strumik for useful discussions. This work was supported in part by the Sherman Fairchild foundation (J.S.), the Gordon and Betty Moore Foundation to Lars Bildsten, Eliot Quataert and E. Sterl Phinney, Simons Investigator awards from the Simons Foundation (E.Q.), NSF grant AST 13-33612 (E.Q.), and by UK STFC and EPSRC grants (A.A.S.).
Group:Walter Burke Institute for Theoretical Physics, TAPIR
Funding AgencyGrant Number
Sherman Fairchild FoundationUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Simons FoundationUNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
Engineering and Physical Sciences Research Council (EPSRC)UNSPECIFIED
Subject Keywords:galaxies: clusters: intracluster medium – magnetic fields – plasmas – turbulence – waves
Issue or Number:2
Record Number:CaltechAUTHORS:20160912-100235395
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Official Citation:J. Squire et al 2016 ApJL 830 L25
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:70278
Deposited By: Tony Diaz
Deposited On:12 Sep 2016 17:25
Last Modified:11 Nov 2021 04:26

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