Large-scale gyrokinetic turbulence simulations: Effects of profile variation

Abstract

Two common computational domains used in gyrokinetic turbulence simulations are a local flux-tube and a global whole plasma volume. The effect of a radially varying pressure gradient is found to explain some of the qualitative differences between these two models. It is shown that a coherent purely radial mode is the result of profile variation. In addition, as profile variation is increased, there is a fairly sudden transition to much lower levels of heat flux. This may explain lower values found in past global simulations. The self-generated purely radial electrostatic potential is found to be 180° out of phase with the flux-surface-averaged ion temperature. A theoretical relation between these two quantities is derived by relating the E×B nonlinearities for ion density and temperature for purely radial modes. This relation is used to explain the various radial mode shapes. Extending these results, a possible scheme is explored to reduce the heat flux by adding a ripple to the ion temperature profile. It may be possible to achieve similar results experimentally using ion cyclotron resonance heating. Finally, simulation results show the additional stabilizing effect of equilibrium Er shear from profile variation in the radial force balance equation.

Massively Parallel Three-Dimensional Toroidal Gyrokinetic Flux-Tube Turbulence Simulation

“…Further application of this model to turbulence and transport simulation results are given in Refs. [33][34][35][36]. This simulation has been used extensively to study ion heat transport.…”

A global collisionless PIC code in magnetic coordinates

“…The global approach is certainly the most realistic model, because it contains the whole radial domain and therefore the effects of profile variation. The aim of this paper is to present the ORB5 code, originally written by Parker [18] and further developed by Tran [13]. ORB5 is a nonlinear gyrokinetic global code which solves the Vlasov-Poisson system in the electrostatic and collisionless limit, and has the unique capability of handling true MHD equilibria [23].…”

“…Various gyrokinetic equations can be found in [9][10][11][12]. Among the different approaches used to solve the gyrokinetic equations, the Particle-In-Cell (PIC) method [8,[13][14][15][16][17][18] is one of the most promising schemes. The distribution function is sampled along trajectories with numerical particles (markers).…”

Global Profile Relaxation and Entropy Dynamics in Turbulent Transport

“…Note that the phase relation between δT (0.0) and ∂ • out of phase). A similar phase relation has been discussed in terms of radial force balance in some other studies [7]. Also, spectral analysis shows that δT (0.0) has almost same wave number (k…”