Three‐dimensional stability of thin quasi‐neutral current sheets

Authors:
  • PPP. L. Pritchett
    P. L. Pritchett
  • FCF. V. Coroniti
    F. V. Coroniti
  • VDV. K. Decyk
    V. K. Decyk
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Abstract
In a thin current sheet (ρi0/L ≲ 1, where ρi0 is the ion gyroradius in the lobe field and L is the current sheet half thickness) of the generalized Harris type, the relative ion‐electron cross‐field drift is comparable to the ion thermal velocity. The three‐dimensional stability properties of such a thin current sheet are investigated by means of nonlocal two‐fluid theory and two‐dimensional and three‐dimensional full particle simulations. As was suggested originally by Zhu et al. [1992], the drift kink mode is found to be of critical importance. For the simple case of no initial Bz field, the fluid theory demonstrates that the drift kink mode is a non‐MHD mode with a polarization structure such that E1y is an antisymmetric function of z while E1z is a symmetric function with E1z(0) ≠ 0. Two‐dimensional (y,z) particle simulations indicate that the nonlinear behavior of this mode is dominated by long‐wavelength modes with kyL ∼ 1 and frequency ωr ∼ Ωi0, where Ωi0 is the ion gyrofrequency in the lobe field. Three‐dimensional particle simulations performed on a massively parallel computer show that while the growth rates for the drift kink mode are reduced by the finite Bz, they can still be appreciable (γ/Ωi0 ≲ 0.05–0.10). The kyL ∼ 1 drift kink modes are always the first to grow in the simulations; subsequently, tearing‐like modes with a dominant kx wave vector also become unstable. Implications of these results for the triggering of substorms are discussed.

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