Understanding the saturation of proton-driven Weibel instabilities and implications for astrophysics
- Department of Mechanical Engineering, Department of Physics and Astronomy, and Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14627 (United States)
The linear growth rate and saturation level of magnetic fields for Weibel instabilities driven by ion temperature anisotropy, defined as {alpha}=(T{sub perpendicular}/T{sub parallel})-1 where T{sub perpendicular} and T{sub parallel} are ion temperatures perpendicular and parallel to the wave vector, are derived in the small {alpha} limit. It is shown that the ratio of the saturated magnetic energy to the initial ion energy scales as the fourth power of the electron to ion mass ratio, m/M, for an initially unmagnetized plasma with {alpha}{<=}M/m. Particle-in-cell simulations confirm the mass scaling and also show that the electron energy gain is of the same order of magnitude as the magnetic field energy. This implies that the Weibel instabilities cannot provide a faster-than-Coulomb collisionless mechanism to equilibrate ion-electron plasmas with ions initially much hotter than electrons, a key component in low-luminosity astrophysical accretion flows. The results here also show that the large {alpha} limit formulas used in the study of magnetic field generation in collisionless shocks are only valid if {alpha}{>=}M/m.
- OSTI ID:
- 20960112
- Journal Information:
- Physics of Plasmas, Vol. 14, Issue 1; Other Information: DOI: 10.1063/1.2409606; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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