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Kinetic simulations of the interruption of large-amplitude shear-Alfvén waves in a high-β plasma

Squire, J. and Kunz, M. W. and Quataert, E. and Schekochihin, A. A. (2017) Kinetic simulations of the interruption of large-amplitude shear-Alfvén waves in a high-β plasma. Physical Review Letters, 119 (15). Art. No. 155101. ISSN 0031-9007. doi:10.1103/PhysRevLett.119.155101.

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Using two-dimensional hybrid-kinetic simulations, we explore the nonlinear "interruption" of standing and traveling shear-Alfvén waves in collisionless plasmas. Interruption involves a self-generated pressure anisotropy removing the restoring force of a linearly polarized Alfvénic perturbation, and occurs for wave amplitudes δB_⊥/B_0≳β^(−1/2) (where β is the ratio of thermal to magnetic pressure). We use highly elongated domains to obtain maximal scale separation between the wave and the ion gyroscale. For standing waves above the amplitude limit, we find that the large-scale magnetic field of the wave decays rapidly. The dynamics are strongly affected by the excitation of oblique firehose modes, which transition into long-lived parallel fluctuations at the ion gyroscale and cause significant particle scattering. Traveling waves are damped more slowly, but are also influenced by small-scale parallel fluctuations created by the decay of firehose modes. Our results demonstrate that collisionless plasmas cannot support linearly polarized Alfvén waves above δB_⊥/B_0∼β^(−1/2). They also provide a vivid illustration of two key aspects of low-collisionality plasma dynamics: (i) the importance of velocity-space instabilities in regulating plasma dynamics at high β, and (ii) how nonlinear collisionless processes can transfer mechanical energy directly from the largest scales into thermal energy and microscale fluctuations, without the need for a scale-by-scale turbulent cascade.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Squire, J.0000-0001-8479-962X
Kunz, M. W.0000-0003-1676-6126
Quataert, E.0000-0001-9185-5044
Schekochihin, A. A.0000-0003-4421-1128
Additional Information:© 2017 American Physical Society. Received 5 May 2017; published 12 October 2017. We thank S. Balbus, S. D. Bale, C. H. K Chen, S. Cowley, B. Dorland, G. Hammett, K. Klein, F. Rincon, L. Sironi, and M. Strumik for useful and enlightening discussions. J. S., A. A. S., and M. W. K. thank the Wolfgang Pauli Institute in Vienna for its hospitality on several occasions. J. S. was funded in part by the Gordon and Betty Moore Foundation through Grant No. GBMF5076 to Lars Bildsten, Eliot Quataert, and E. Sterl Phinney. E. Q. was supported by Simons Investigator awards from the Simons Foundation and NSF Grant No. AST 13-33612. A. A. S. was supported in part by grants from UK STFC and EPSRC. M. W. K. was supported in part by NASA Grant No. NNX16AK09G and U.S. DOE Award No. DE-AC02-09-CH11466.
Group:Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Gordon and Betty Moore FoundationGBMF5076
Simons FoundationUNSPECIFIED
NSFAST 13-33612
Science and Technology Facilities Council (STFC)UNSPECIFIED
Engineering and Physical Sciences Research Council (EPSRC)UNSPECIFIED
Department of Energy (DOE)DE-AC02-09-CH11466
Issue or Number:15
Record Number:CaltechAUTHORS:20170724-083035495
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79285
Deposited By: Tony Diaz
Deposited On:24 Jul 2017 15:59
Last Modified:15 Nov 2021 17:47

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