Collisional damping of zonal flows due to finite Larmor radius effects

Abstract

The collisional damping of seeded E ϫ B zonal flows on the ion Larmor radius scale is studied using a gyrokinetic model. The focus is on flow damping due to finite Larmor radius effects, which cause a v ʈ / v anisotropy of the ion distribution function that is damped by ion-ion collisions. The gyrokinetic equations are solved in a slab geometry with no gradients or curvature, and a gyroaveraged Lorentz collision operator that conserves particle number, momentum, and energy is used. The solution of the gyrokinetic equations explores the dependence of the damping rate on the wavelength of the flows and the impact of the collisions on the ion distribution function. These numerical results can be used as a benchmark test during the implementation of finite Larmor radius effects in the collision operator of gyrokinetic codes.

Gyrokinetic simulations of plasma turbulence in a Z-pinch using a moment-based approach and advanced collision operators

“…With a Dimits threshold identified around κ N ∼ 2 in the collisionless case, the influence of collisions on the transport level becomes particularly evident for κ N < 2. This confirms previous studies (Lin et al 1999;Ricci et al 2006a;Ricci, Rogers & Dorland 2010) pointing that collisional effects are mainly related to the dynamics of the ZF. Our results highlight the disagreement between Dougherty, Sugama, Lorentz and Coulomb GK collision models, in the linear growth rate and, even more, in the level of nonlinear transport.…”

“…1999; Ricci et al. 2006 a ; Ricci, Rogers & Dorland 2010) pointing that collisional effects are mainly related to the dynamics of the ZF. Our results highlight the disagreement between Dougherty, Sugama, Lorentz and Coulomb GK collision models, in the linear growth rate and, even more, in the level of nonlinear transport.…”

Excitation of zonal flow by intermediate-scale toroidal electron temperature gradient turbulence

“…In deriving equation (4), we closely follow reference [15]. The difference in linear terms is that we introduce an ad hoc gyrodiffusive contribution (∝d z ∼ O( 1)) to the ZF collisional damping rate, of which the importance has been emphasized recently [16]. It can enhance the ZF collisional damping, and, thereby, may suppress the short wavelength ZFs [16].…”

“…The difference in linear terms is that we introduce an ad hoc gyrodiffusive contribution (∝d z ∼ O( 1)) to the ZF collisional damping rate, of which the importance has been emphasized recently [16]. It can enhance the ZF collisional damping, and, thereby, may suppress the short wavelength ZFs [16]. However, noting that the gyrodiffusive term is algebraic with respect to θ k , it turns out that this effect is not effective for the long wavelength ZFs (k 2 z ρ 2 e q 2 1) considered in this work, as shown later.…”

Study of Coulomb collisional effects on the propagation of electromagnetic waves in a turbulent plasma

“…A collisional Weibel instability has been investigated by many authors in recent years. [16,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Stress effect has been neglected in the calculation of the growth rate of the collisional Weibel instability in laser-plasma interaction. The unstable Weibel mode, driven by the anisotropy in the distribution function caused by the heat flow, can have significant growth rates occurring at densities above critical.…”