Influence of Atomic Physics on EDGE2D-EIRENE Simulations of JET Divertor Detachment with Carbon and Beryllium/Tungsten Plasma-Facing Components

The EDGE2D-EIRENE code is applied for simulation of divertor detachment during matched density ramp experiments in high triangularity, L-mode plasmas in both JETC and JET-ILW. The code runs without drifts and includes either C or Be as impurity, but not W, assuming that the W targets have been coated with Be via main chamber migration. The simulations reproduce reasonably well the observed particle flux detachment as density is raised in both JET-C and JET-ILW experiments and can better match the experimental in-out divertor target power asymmetry if the heat flux entering the outer divertor is artificially set at around 2-3 times that entering the inner divertor. A careful comparison between different sets of atomic physics processes used in EIRENE shows that ion-molecule elastic collisions are required for the detachment seen in the EDGE2D-EIRENE simulations. This process provides good neutral confinement in the divertor at low temperature inherent for detachment. Comparison between EDGE2D-EIRENE and SOLPS4.3 simulations of the density ramp in C shows that the detachment trends are similar, but the importance of the ionmolecule elastic collisions is reduced in SOLPS4.3. Both codes suggest that any process capable of improving the neutral confinement in the divertor should help to improve the modelling of the detachment. A further outcome of this work has been to demonstrate that key JET divertor diagnostic signals ­ Langmuir probe electron temperatures and bolometric tomographic reconstructions ­ are running in the limit of validity in high recycling and detached conditions and cannot be reliably used for code validation. The simulations do, however, reproduce rather well the evolution of the line integrated bolometer chord measurements. Estimates made with a model accounting for plasma resistivity can also bring the electron temperature derived from Langmuir probes closer to the simulation results. The comparison between the code results and high-n Balmer line radiation intensity profiles indicates that a strong volume recombination source is present during the detachment and may play a role in this process.
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