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Firehose and mirror instabilities in a collisionless shearing plasma

Author(s): Kunz, Matthew W.; Schekochihin, AA; Stone, James M

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Abstract: Hybrid-kinetic numerical simulations of firehose and mirror instabilities in a collisionless plasma are performed in which pressure anisotropy is driven as the magnetic field is changed by a persistent linear shear S. For a decreasing field, it is found that mostly oblique firehose fluctuations grow at ion Larmor scales and saturate with energies ∝S1/2; the pressure anisotropy is pinned at the stability threshold by particle scattering off microscale fluctuations. In contrast, nonlinear mirror fluctuations are large compared to the ion Larmor scale and grow secularly in time; marginality is maintained by an increasing population of resonant particles trapped in magnetic mirrors. After one shear time, saturated order-unity magnetic mirrors are formed and particles scatter off their sharp edges. Both instabilities drive sub-ion-Larmor-scale fluctuations, which appear to be kinetic-Alfvén-wave turbulence. Our results impact theories of momentum and heat transport in astrophysical and space plasmas, in which the stretching of a magnetic field by shear is a generic process. © 2014 American Physical Society.
Publication Date: 23-May-2014
Citation: Kunz, MW, Schekochihin, AA, Stone, JM. (2014). Firehose and mirror instabilities in a collisionless shearing plasma. Physical Review Letters, 112 (20), 10.1103/PhysRevLett.112.205003
DOI: doi:10.1103/PhysRevLett.112.205003
ISSN: 0031-9007
EISSN: 1079-7114
Pages: 205003-1 to 205003-6
Type of Material: Journal Article
Journal/Proceeding Title: Physical Review Letters
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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