Gyrokinetic continuum simulation of turbulence in a straight open-field-line plasma

Abstract

Five-dimensional gyrokinetic continuum simulations of electrostatic plasma turbulence in a straight, open-field-line geometry have been performed using a full-f discontinuous-Galerkin approach implemented in the Gkeyll code. While various simplifications have been used for now, such as long-wavelength approximations in the gyrokinetic Poisson equation and the Hamiltonian, these simulations include the basic elements of a fusion-device scrape-off layer: localised sources to model plasma outflow from the core, cross-field turbulent transport, parallel flow along magnetic field lines, and parallel losses at the limiter or divertor with sheath-model boundary conditions. The set of sheath-model boundary conditions used in the model allows currents to flow through the walls. In addition to details of the numerical approach, results from numerical simulations of turbulence in the Large Plasma Device, a linear device featuring straight magnetic field lines, are presented.

Gyrokinetic full-f particle-in-cell simulations on open field lines with PICLS

“…As mentioned before already, the quantitative differences of our results compared to the previous continuum code results from Pan et al 17 and Shi et al 16 are mainly based on our PIC-specific implementation of the velocity distribution functions. We assume that the sources we implemented allow faster particles than the sources used in the mentioned studies.…”

“…2in Pan et al17 andFig. 3in Shi et al16 ) show a similar increase of the total heat flux to ∼ 0.5 × 10 9 W/m 2 in this time period, however the ion heat flux increases as much as the electron flux drops at 0.5τ e and remains higher for the rest of their simulations. In case of simulations with a fully-kinetic PIC code (Fig.…”

“…As shown in Shi et al 16 , a simplified polarization equation can be obtained. This is derived from a dispersion relation resulting from linearising eq.…”

“…11,13,14 In very recent works the same problem was simulated with gyrokinetic continuum codes and the results of the previous works could be reproduced. [15][16][17] Additionally, both implemented logical-sheath boundary conditions 18 , that are designed to provide the effects of a Debye sheath, while not actually having to resolve it. Hence, the combination of gyrokinetics and a logical sheath delivers a significant speed up, compared to kinetic codes, since the restriction towards time steps of ≈ ω −1 ce and spatial resolutions of ≈ λ De is lifted.…”

Nonlinear gyrokinetic Coulomb collision operator

“…This is especially relevant in the high-temperature tokamak H-mode regime (Zweben et al 2007), the regime of operation relevant for ITER and future devices. Despite recent progress (Chang et al 2017;Shi et al 2017;Pan et al 2018), overcoming the limitation of the drift-reduced fluid models in the description of the tokamak periphery region by using a gyrokinetic model valid at k ⊥ ρ i ∼ 1 has proven to be exceptionally demanding. Among the numerous challenges, the effort is undermined by the lack of a proper collisional gyrokinetic model for the periphery.…”