Hermes: global plasma edge fluid turbulence simulations

Abstract

Abstract. The transport of heat and particles in the relatively collisional edge regions of magnetically confined plasmas is a scientifically challenging and technologically important problem. Understanding and predicting this transport requires the self-consistent evolution of plasma fluctuations, global profiles and flows, but the numerical tools capable of doing this in realistic (diverted) geometry are only now being developed.Here a 5-field reduced 2-fluid plasma model for the study of instabilities and turbulence in magnetised plasmas is presented, built on the BOUT++ framework. This cold ion model allows the evolution of global profiles, electric fields and flows on transport timescales, with flux-driven cross-field transport determined self-consistently by electromagnetic turbulence. Developments in the model formulation and numerical implementation are described, and simulations are performed in poloidally limited and diverted tokamak configurations.

The effects of non-uniform drive on plasma filaments

“…While there have been many models implemented in BOUT++, we choose here the Hermes model [9,10] for several reasons. Firstly, a pellet cloud represents a large perturbation in the local density, and therefore a full-profile model which does not use the Boussinesq approximation should be used.…”

“…A more complete description of the open-source Hermes model can be found in Reference [9], but the model is repeated here for clarity. The plasma equations assume cold ions, and evolve the plasma (electron) density n, electron thermal pressure p e = nT e , and vorticity ω, parallel ion momentum nv ||i and a form of Ohm's law:…”

Effect of the Boussinesq approximation: Turbulence studies with GRILLIX in slab geometry

“…Nevertheless, one obtains a consistent delta‐f energy, which must be conserved when applying the Boussinesq approximation. A conservative form of the Boussinesq approximation is shown in …”

“…The Boussinesq approximation is widely used in the plasma turbulence community. [8][9][10][11] The main point of it is the assumption that the fluctuations of the density are very small compared to the background, such that one neglects the spatial and temporal dependence of the density (n(x, y, z, t) → n 0 = 1) in the vorticity equation, leading to a simplification. It is important to retain the conservation properties of ⋅ j = 0.…”

Full-f gyrokinetic simulation of turbulence in a helical open-field-line plasma

“…[48][49][50] Recent fluid simulations are also including finite T i . 51,52 Although our simulations do not yet simultaneously contain open-and closed-field-line regions, [51][52][53][54][55][56] we believe that many basic properties of SOL turbulence and transport are reproduced in this model. Additionally, the turbulence in this helical open-field-line geometry with parameters appropriate for a tokamak SOL has not been previously studied using a gyrokinetic PIC approach, either.…”