Renormalized dielectric function for collisionless drift wave turbulence

Abstract

Earlier renormalized theories for collisionless drift wave turbulence were deficient in several respects when ω<kzvi and the principal perpendicular motion is the E×B drift. The earlier theories did not preserve the perpendicularity between the E×B ion current and the electric field E and consequently, did not conserve energy. In addition, earlier theories did not correctly treat the case ni∼eφ/T in which the nonlinear convective term -φ×B⋅-ni should be very small. These problems are analyzed and corrected in a new version. The new theory predicts that drift wave energy is converted into parallel ion energy, producing a damping rate γ∥=−(kzvi/ω)2 k⊥2D, where D is a test particle diffusion coefficient. For a fluctuating potential φ due only to drift waves, D is greater than zero only when the threshold eφ/T∼ (k⊥Ln)−1 for ion stochastic motion is exceeded. The nonlinear stabilization will occur slightly above this threshold if γe/ω< (kzvi/ω)2 (γe is the linear growth rate). For this case the density diffusion coefficient Dn (which is less than D) will be Dn∼γe/k⊥2.