A hybrid fluid–kinetic neutral model based on a micro–macro decomposition in the SOLPS‐ITER plasma edge code suite

Abstract

We present a hybrid fluid-kinetic model for the hydrogenic atoms in the plasma edge, which is implemented in SOLPS-ITER. A micro-macro decomposition of the kinetic equation leads to a fluid model with a continuity and parallel momentum equation (implemented in B2.5) coupled to a kinetic correction equation (implemented in EIRENE). We assess the hybrid model for a high recycling fixed background plasma. The hybrid approach leads to a reduction of the CPU time to obtain the same statistical error as the full kinetic Monte Carlo (MC) simulation with approximately factors 1.7, 4.9, and 1.9 for respectively the particle, parallel momentum, and electron energy source. However, there is a CPU time increase for the ion energy source. By comparing the results with our in-house plasma edge code, we conclude that the hybrid performance can be improved by adapting some default MC features in EIRENE.

Combination of micro–macro and spatially hybrid fluid‐kinetic approach for hydrogenic plasma edge neutrals

“…By combining the spatially hybrid approach from Reference [6] with the micro–macro approach from Reference [8], we add a kinetic correction on top of the fluid part. This automatic correction is especially successful for the treatment of atoms resulting from molecular dissociation, which were recommended to be treated as a fluid in the original spatially hybrid approach to reduce the computational cost, at the expense of accuracy.…”

“…A fully kinetic MC approach is still used for Equation (6), whereas the micro-macro approach described in Section 3.2 is used for Equation (7). As implemented in this way, source strata for which a fully kinetic treatment is required (e.g., to model the transport in the void regions) and strata for which the micro-macro approach becomes inefficient due to long particle mean free paths [8] , can still be treated fully kinetically.…”

“…The kinetic correction terms in Equations ( 10)-( 15) follow from an MC simulation of the micro equation, which is obtained by plugging Equation (8) in Equation (7). After re-arranging the terms, this gives…”

“…To correct for errors from the fluid atom model in the plasma grid region without the need for a user‐defined criterion to determine the fluid and kinetic regions, a micro–macro approach has been developed. [ 8 ] However, this method has only been assessed for a very simplified rectangular slab case without void regions and molecules, and assuming a fixed plasma background. In this contribution, we combine the spatially hybrid and micro–macro approach to simulate realistic geometries including the coupling to kinetic molecules and fluid plasma.…”

Advanced spatially hybrid fluid‐kinetic modelling of plasma‐edge neutrals and application to ITER case using SOLPS‐ITER

“…At the same time, it is well known that this fluid approach for the neutrals is only a good approximation in the HCRs, but not in the entire plasma edge, and not even in the entire divertor. Therefore, different hybrid fluid-kinetic neutral models are being pursued, which aim to combine the benefits of a kinetic and fluid approach in an efficient way [10,1,6,13,8]. In the standard spatially hybrid models developed in Refs.…”