Abstract
The suppression of edge-localized modes (ELMs) by applying resonant magnetic perturbations (RMPs) is well studied in low collisionality deuterium plasmas as a measure to reduce transient divertor heat loads. However, ELM suppression has yet to be demonstrated in non-nuclear fuels such as hydrogen and hydrogen + helium mixtures which are the main ion species to be used in the ITER pre-fusion power operation (PFPO) phase. For the first time, attempts have been made to access ELM suppression with RMPs in ITER-like low collisionality hydrogen plasmas at DIII-D and ASDEX Upgrade. The DIII-D experiments focused on operation with injected power slightly above the L-H power threshold similar to the expected conditions in the ITER PFPO phase with limited external heating power. The RMPs were found to trigger H-L backtransitions, which is shown to be avoided by reducing the L-H power threshold by diluting the plasma with helium. The additional helium combined with a larger measured neutral density of hydrogen inside the separatrix compared to ELM suppressed deuterium plasmas precluded access to a pedestal top density below the known RMP-ELM suppression threshold. At ASDEX Upgrade, RMP-ELM suppression has been achieved when the concentration of1H in the hydrogen isotope mix is below 40 % . While all known access criteria for RMP-ELM suppression were met above this threshold, full ELM suppression was replaced by strong mitigation. The most prominent difference between the hydrogen and deuterium plasmas was a change of turbulence characteristics in the pedestal where Doppler reflectometry measurements suggest a significant reduction of turbulence even at small hydrogen concentrations. In conclusion, these experiments not only identify issues that may prevent access to RMP-ELM suppression in the ITER PFPO phase, but also highlight missing physics in our current understanding of RMP-ELM suppression such as potentially the role of turbulence in the pedestal gradient region.
| Original language | English |
|---|---|
| Article number | 026017 |
| Journal | Nuclear Fusion |
| Volume | 64 |
| Issue number | 2 |
| DOIs | |
| State | Published - Feb 2024 |
| Externally published | Yes |
Funding
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Awards DE-FC02-04ER54698, DE-SC0021968, DE-SC0022270, DE-SC0020284, DE-AC52-07NA27344, DE-FG02-05ER54809 and DE-SC0020287. 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—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.
| Funders | Funder number |
|---|---|
| DOE Office of Science user facility | DE-SC0020287, DE-SC0020284, DE-FG02-05ER54809, DE-FC02-04ER54698, DE-SC0021968, DE-SC0022270, DE-AC52-07NA27344 |
| U.S. Department of Energy | |
| Office of Science | |
| Fusion Energy Sciences | |
| European Commission | 101052200—EUROfusion |
Keywords
- edge-localized modes
- hydrogen
- resonant magnetic perturbations
- suppression
