COLLISIONLESS ISOTROPIZATION of the SOLAR-WIND PROTONS by COMPRESSIVE FLUCTUATIONS and PLASMA INSTABILITIES

Daniel Verscharen, Benjamin D.G. Chandran, Kristopher G. Klein, Eliot Quataert

Research output: Contribution to journalArticlepeer-review

38 Scopus citations

Abstract

Compressive fluctuations are a minor yet significant component of astrophysical plasma turbulence. In the solar wind, long-wavelength compressive slow-mode fluctuations lead to changes in and in , where and are the perpendicular and parallel temperatures of the protons, B is the magnetic field strength, and is the proton density. If the amplitude of the compressive fluctuations is large enough, crosses one or more instability thresholds for anisotropy-driven microinstabilities. The enhanced field fluctuations from these microinstabilities scatter the protons so as to reduce the anisotropy of the pressure tensor. We propose that this scattering drives the average value of away from the marginal stability boundary until the fluctuating value of stops crossing the boundary. We model this "fluctuating-anisotropy effect" using linear Vlasov-Maxwell theory to describe the large-scale compressive fluctuations. We argue that this effect can explain why, in the nearly collisionless solar wind, the average value of is close to unity.

Original languageEnglish (US)
Article number128
JournalAstrophysical Journal
Volume831
Issue number2
DOIs
StatePublished - Nov 10 2016
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • accretion, accretion disks
  • instabilities
  • plasmas
  • solar wind
  • turbulence
  • waves

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