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Title: Effects of electron temperature anisotropy on proton mirror instability evolution: KINETIC WAVES AND INSTABILITIES

 [1];  [2];  [2]
  1. Department of Physics, University of New Hampshire, Durham New Hampshire USA
  2. Department of Physics and Space Science Center, University of New Hampshire, Durham New Hampshire USA
Publication Date:
Sponsoring Org.:
OSTI Identifier:
Grant/Contract Number:
DESC0006670; PHY-1229408; TG-MCA98N022
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Volume: 121; Journal Issue: 6; Related Information: CHORUS Timestamp: 2017-10-23 17:32:01; Journal ID: ISSN 2169-9380
Wiley Blackwell (John Wiley & Sons)
Country of Publication:
United States

Citation Formats

Ahmadi, Narges, Germaschewski, Kai, and Raeder, Joachim. Effects of electron temperature anisotropy on proton mirror instability evolution: KINETIC WAVES AND INSTABILITIES. United States: N. p., 2016. Web. doi:10.1002/2016JA022429.
Ahmadi, Narges, Germaschewski, Kai, & Raeder, Joachim. Effects of electron temperature anisotropy on proton mirror instability evolution: KINETIC WAVES AND INSTABILITIES. United States. doi:10.1002/2016JA022429.
Ahmadi, Narges, Germaschewski, Kai, and Raeder, Joachim. 2016. "Effects of electron temperature anisotropy on proton mirror instability evolution: KINETIC WAVES AND INSTABILITIES". United States. doi:10.1002/2016JA022429.
title = {Effects of electron temperature anisotropy on proton mirror instability evolution: KINETIC WAVES AND INSTABILITIES},
author = {Ahmadi, Narges and Germaschewski, Kai and Raeder, Joachim},
abstractNote = {},
doi = {10.1002/2016JA022429},
journal = {Journal of Geophysical Research. Space Physics},
number = 6,
volume = 121,
place = {United States},
year = 2016,
month = 6

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1002/2016JA022429

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  • Cited by 1
  • We investigate the role of kinetic instabilities driven by a proton anisotropy on the onset of magnetic reconnection by means of two-dimensional hybrid simulations. The collisionless tearing of a current sheet is studied in the presence of a proton temperature anisotropy in the surrounding plasma. Our results confirm that anisotropic protons within the current sheet region can significantly enhance/stabilize the tearing instability of the current. Moreover, fluctuations associated with linear instabilities excited by large proton temperature anisotropies can significantly influence the stability of the plasma and perturb the current sheets, triggering the tearing instability. We find that such a complexmore » coupling leads to a faster tearing evolution in the T{sub Up-Tack} > T{sub ||} regime when an ion-cyclotron instability is generated by the anisotropic proton distribution functions. On the contrary, in the presence of the opposite anisotropy, fire-hose fluctuations excited by the unstable background protons with T{sub ||} < T{sub Up-Tack} are not able to efficiently destabilize current sheets, which remain stable for a long time after fire-hose saturation. We discuss possible influences of this novel coupling on the solar wind and heliospheric plasma dynamics.« less
  • The standard magnetohydrodynamic (MHD) theory predicts that the Alfvén wave may become fire-hose unstable for β{sub ∥}−β{sub ⊥}>2. In this study, we examine the proton fire-hose instability (FHI) based on the gyrotropic two-fluid model, which incorporates the ion inertial effects arising from the Hall current and electron temperature anisotropy but neglects the electron inertia in the generalized Ohm's law. The linear dispersion relation is derived and analyzed which in the long wavelength approximation, λ{sub i}k→0 or α{sub e}=μ{sub 0}(p{sub ∥,e}−p{sub ⊥,e})/B{sup 2}=1, recovers the ideal MHD model with separate temperature for ions and electrons. Here, λ{sub i} is the ionmore » inertial length and k is the wave number. For parallel propagation, both ion cyclotron and whistler waves become propagating and growing for β{sub ∥}−β{sub ⊥}>2+λ{sub i}{sup 2}k{sup 2}(α{sub e}−1){sup 2}/2. For oblique propagation, the necessary condition for FHI remains to be β{sub ∥}−β{sub ⊥}>2 and there exist one or two unstable fire-hose modes, which can be propagating and growing or purely growing. For large λ{sub i}k values, there exists no nearly parallel FHI leaving only oblique FHI and the effect of α{sub e}>1 may greatly enhance the growth rate of parallel and oblique FHI. The magnetic field polarization of FHI may be reversed due to the sign change associated with (α{sub e}−1) and the purely growing FHI may possess linear polarization while the propagating and growing FHI may possess right-handed or left-handed polarization.« less
  • The authors examine the effect of finite electron temperatures on the growth rate of proton mirror instabilities. They find that if the electron temperature is comparable with the parallel proton temperature that the mirror instability growth rate is slowed by the presence of a parallel electric field. This field is generated as a result of pressure gradients in the electron distribution. These finite electron temperature effects are seen to have little impact on the thresholds for the instability, but to impact the growth rate, compressibility, and polarization much more strongly.
  • In this paper the simultaneous nonlinear evolution of the Alfven-ion-cyclotron and mirror instabilities driven by an anisotropic ion distribution function are studied. The ions are modeled by a bi-Maxwellian distribution function. For the sake of generality, two ion components are considered; the initially isotropic component and a population possessing a large temperature anisotropy with perpendicular temperature greater than parallel temperature. Here, perpendicular and parallel are defined with respect to the ambient magnetic field. The analysis is based on quasilinear kinetic theory. It is shown that initially, the mirror mode grows at a slightly faster rate when compared with the ion-cyclotronmore » mode, but the subsequent evolution shows that the ion-cyclotron mode saturates at a much larger intensity. Simultaneously, large perpendicular temperature associated with the anisotropic ions is substantially reduced as the free energy is taken away by the unstable waves, while the parallel temperature increases so as to reduce the anisotropy. The initially isotropic ions, on the other hand, are also heated in the direction perpendicular to the ambient magnetic field vector.« less