Understanding the saturation of proton-driven Weibel instabilities and implications for astrophysics

作者：Ren Chuang^*; Blackman Eric G; Fong Wen fai

来源：Physics of Plasmas, 2007, 14(1): 012901.

DOI：10.1063/1.2409606

The linear growth rate and saturation level of magnetic fields for Weibel instabilities driven by ion temperature anisotropy, defined as alpha=(T-perpendicular to/T-parallel to)-1 where T-perpendicular to and T-parallel to 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.

• 出版日期2007-1