Abstract
Both experiments and simulations with SOLPS-ITER and EDGE2D-EIRENE show that the onset of detachment for the low-field side (LFS) divertor – defined here as the line-averaged upstream density (〈ne〉edge) at which the plasma flux to the LFS target (ILFS−plate) starts to decrease with increasing 〈ne〉edge – is independent of the isotope mass. However, there are three major simulation-experiment discrepancies: (i) the absolute values of ILFS−plate and the electron density (ne) in the LFS divertor at the onset of detachment are significantly lower in simulations, i.e., approximately a factor of 2 for ILFS−plate and a factor of 3-4 for ne; (ii) the degree of detachment – defined here as the difference between ILFS−plate at the onset of detachment and at an 〈ne〉edge value close to the density limit – is smaller in simulations compared to experiments; and (iii) the experimentally observed larger degree of detachment for D and T plasmas compared to H plasmas cannot be clearly distinguished from the simulation results. There are strong indications that discrepancy (i) is to a large extent caused by neglecting Lyman-opacity effects in our simulations. The simulations predict a similar net volumetric recombination source for all isotopes due to the fact that molecule-activated recombination (MAR) compensates for the reduced electron–ion recombination (EIR) for H, whereas MAR is negligible for D and T. This similar net volumetric recombination source for all isotopes leads to an isotope-independent degree of detachment in simulations. An analysis of the Balmer-α and Balmer-γ emission confirms the underestimate of MAR in simulations (especially for D and T) for the JET metallic wall, which was previously observed for devices with a carbon wall. The underestimate of MAR is an important cause for discrepancy (ii) and the fact that there is a stronger underestimate of MAR for D and T than for H explains discrepancy (iii). Extending the plasma grid to the vessel wall increases ILFS−plate and ne at the onset of detachment by 25%, and the EIR source increases by 80% in detached conditions. Hence, while the extended grid results are closer to the experimental observations, the previously described qualitative discrepancies still persist.
| Original language | English |
|---|---|
| Article number | 101842 |
| Journal | Nuclear Materials and Energy |
| Volume | 42 |
| DOIs | |
| State | Published - Mar 2025 |
Funding
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 \u2014 EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization. N. Horsten is a postdoctoral research fellow of the Research Foundation Flanders (FWO) under grant number 12AES24N. The computational resources and services used in this work were provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation Flanders (FWO) and the Flemish Government - department EWI.
| Funders | Funder number |
|---|---|
| Vlaams Supercomputer Centrum | |
| Flemish Government - department EWI | |
| European Commission | 101052200 — EUROfusion |
| Fonds Wetenschappelijk Onderzoek | 12AES24N |
Keywords
- Balmer emission
- Divertor detachment
- Lyman opacity
- Plasma edge code validation
