A STRINGENT LIMIT on the AMPLITUDE of ALFVÉNIC PERTURBATIONS in HIGH-BETA LOW-COLLISIONALITY PLASMAS

J. Squire, E. Quataert, A. A. Schekochihin

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

It is shown that low-collisionality plasmas cannot support linearly polarized shear-Alfvén fluctuations above a critical amplitude δB/B0 ∼ B-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.

Original languageEnglish (US)
Article numberL25
JournalAstrophysical Journal Letters
Volume830
Issue number2
DOIs
StatePublished - Oct 20 2016

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • galaxies: clusters: intracluster medium
  • magnetic fields
  • plasmas
  • turbulence
  • waves

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