Three-dimensional Monte Carlo simulations of W7-X plasma transport: density control and particle balance in steady-state operations

Abstract

This paper presents self-consistent three-dimensional (3D) plasma transport simulations in the boundary of stellarator W7-X obtained with the Monte Carlo code EMC3-EIRENE for three typical island divertor configurations. The chosen 3D grid consists of relatively simple nested finite toroidal surfaces defined on a toroidal field period and covering the whole edge topology, which includes closed surfaces, islands and ergodic regions. Local grid refinements account for the required high resolution in the divertor region. The distribution of plasma density and temperature in the divertor region, as well as the power deposition profiles on the divertor plates, are shown to strongly depend on the island geometry, i.e. on the position and size of the dominant island chain. Configurations with strike-point positions closer to the gap of the divertor chamber generally favour the neutral compression in the divertor chamber and hence the pumping efficiency. The ratio of pumping to recycling fluxes is found to be roughly independent of the separatrix density and is thus a figure of merit for the quality of the configuration and of the divertor system in terms of density control. Lower limits for the achievable separatrix density, which determine the particle exhaust capabilities in stationary conditions, are compared for the three W7-X configurations.

3D simulations of gas puff effects on edge plasma and ICRF coupling in JET

“…These free parameters can be derived through comparisons of the simulated plasma parameters with the experimental ones. Besides its wide applications in stellarators [28,29], EMC3-EIRENE is also attracting extensive interest for its implementation in tokamaks where some 3D SOL physics aspects need to be accounted. For example, the code was applied to model ICRF antenna coupling experiments [6,8], the influences of the Resonant Magnetic Perturbation fields [30], the 3D edge plasma convection [20] and the plasma-wall interactions [20,31].…”

Momentum correction techniques for neoclassical transport in stellarators

“…10, the bootstrap current is too large, i.e. the edge is in conflict with a proper operation of the island divertor [39,40]. In principle, one might reduce the vacuum by the amount the bootstrap current supplies for stationary conditions, i.e.…”

3D Studies of the Island Divertor Transport inW7-X

“…A simple impurity transport model is coupled self-consistently with the plasma-neutral transport in the code EMC3-EIRENE for examining the primary effects of power radiated by the impurities on the first self-consistently simulated plasma distributions presented in Ref [1]. For the analysis using the magnetic configuration represented by case II the plasma model adopted for self-consistent computations presented in [1] is extended further to include the effects of this impurity transport model which accounts for the conservation, respectively, of particles and momentum,…”

“…Among the important investigations using three-dimensional edge plasma simulations with code combination EMC3-EIRENE, the first self-consistent plasma-neutral transport characterization was completed recently [1] and the possibility of achieving optimized plasma conditions was investigated in various W7-X edge magnetic configurations. The main objectives remain to explore the optimum island divertor performance for successful stationary operation and an effective control of power load on the targets which may be achieved by exploiting the intrinsic stochasticity of magnetic configurations and also by means of radiation driven detached divertor plasma conditions.…”

“…The results are analyzed with respect to the effects of stochasticity associated with three major magnetic configurations. For the study of impurity transport and the impact of impurity radiation on the edge plasma conditions, the results of previous self-consistent plasma-neutral computations [1] are also extended further by inclusion of an additional impurity transport model. In the high density regime where the temperature is low enough and impurity radiation begins to play a role in the energy balance, the radiated fraction of total input power is computed for the steady-state operating conditions with various values of separatrix density.…”