Anisotropy of turbulence in a collisionless shock

Abstract

We have measured the level of density fluctuations 〈δn_e²(K)〉 for ‖K‖ ∼ 1/λ_D as a function of the angle between k and the current within a collisionless shock. The cut-off angle is in good agreement with that predicted for current-driven ion wave turbulence and one-dimensional heating of the ions. This agreement provides further evidence that ion-wave instability is responsible for the observed turbulence within the shock.