TY - JOUR
T1 - COLLISIONLESS ISOTROPIZATION of the SOLAR-WIND PROTONS by COMPRESSIVE FLUCTUATIONS and PLASMA INSTABILITIES
AU - Verscharen, Daniel
AU - Chandran, Benjamin D.G.
AU - Klein, Kristopher G.
AU - Quataert, Eliot
N1 - Publisher Copyright:
© 2016. The American Astronomical Society. All rights reserved.
PY - 2016/11/10
Y1 - 2016/11/10
N2 - 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.
AB - 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.
KW - accretion, accretion disks
KW - instabilities
KW - plasmas
KW - solar wind
KW - turbulence
KW - waves
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U2 - 10.3847/0004-637X/831/2/128
DO - 10.3847/0004-637X/831/2/128
M3 - Article
AN - SCOPUS:84994523005
SN - 0004-637X
VL - 831
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 128
ER -