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Title: Kinetic Simulations of the Interruption of Large-Amplitude Shear-Alfvén Waves in a High- β Plasma

Abstract

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 0–1/2. Here, 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 energymore » and microscale fluctuations, without the need for a scale-by-scale turbulent cascade.« less

Authors:
 [1];  [2];  [3];  [4]
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States); Walter Burke Institute for Theoretical Physics, Pasadena, CA (United States)
  2. Princeton Univ., Princeton, NJ (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  3. Univ. of California, Berkeley, CA (United States)
  4. Univ. of Oxford, Oxford (United Kingdom); Merton College, Oxford (United Kingdom)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1404881
Alternate Identifier(s):
OSTI ID: 1399168
Grant/Contract Number:  
GBMF5076; AST 13-33612; ACI-1548562; NNX16AK09G; AC02-09CH11466
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 119; Journal Issue: 15; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Squire, J., Kunz, M. W., Quataert, E., and Schekochihin, A. A. Kinetic Simulations of the Interruption of Large-Amplitude Shear-Alfvén Waves in a High-β Plasma. United States: N. p., 2017. Web. doi:10.1103/PhysRevLett.119.155101.
Squire, J., Kunz, M. W., Quataert, E., & Schekochihin, A. A. Kinetic Simulations of the Interruption of Large-Amplitude Shear-Alfvén Waves in a High-β Plasma. United States. doi:10.1103/PhysRevLett.119.155101.
Squire, J., Kunz, M. W., Quataert, E., and Schekochihin, A. A. Thu . "Kinetic Simulations of the Interruption of Large-Amplitude Shear-Alfvén Waves in a High-β Plasma". United States. doi:10.1103/PhysRevLett.119.155101. https://www.osti.gov/servlets/purl/1404881.
@article{osti_1404881,
title = {Kinetic Simulations of the Interruption of Large-Amplitude Shear-Alfvén Waves in a High-β Plasma},
author = {Squire, J. and Kunz, M. W. and Quataert, E. and Schekochihin, A. A.},
abstractNote = {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⊥/B0≳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⊥/B0~β–1/2. Here, 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.},
doi = {10.1103/PhysRevLett.119.155101},
journal = {Physical Review Letters},
number = 15,
volume = 119,
place = {United States},
year = {Thu Oct 12 00:00:00 EDT 2017},
month = {Thu Oct 12 00:00:00 EDT 2017}
}

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