Abstract
Impurity seeding studies in the small angle slot (SAS) divertor at DIII-D have revealed a strong relationship between the detachment onset and pedestal characteristics with both target geometry and impurity species. N2 seeding in the slot has led to the first simultaneous observation of detachment on the entire suite of boundary diagnostics viewing the SAS without degradation of core confinement. SOLPS-ITER simulations with D+C+N, full cross field drifts, and n-n collisions activated are performed for the first time in DIII-D to interpret the behavior. This highlights a strong effect of divertor configuration and plasma drifts on the recycling source distribution with significant consequences on plasma flows. Flow reversal is found for both main ions and impurities affecting strongly the impurity transport and providing an explanation for the observed dependence on the strike point location of the detachment onset and impurity leakage found in the experiments. Matched discharges with either nitrogen or neon injection show that while nitrogen does not significantly affect the pedestal, neon leads to increased pedestal pressure gradients and improved pedestal stability. Little nitrogen penetrates in the core, but a significant amount of neon is found in the pedestal consistent with the different ionization potentials of the two impurities. This work demonstrates that neutral and impurity distributions in the divertor can be controlled through variations in strike point locations in a fixed baffle structure. Divertor geometry combined with impurity seeding enables mitigated divertor heat flux balancing core contamination, thus leading to enhanced divertor dissipation and improved core-edge compatibility, which are essential for ITER and for future fusion reactors.
| Original language | English |
|---|---|
| Article number | 062506 |
| Journal | Physics of Plasmas |
| Volume | 27 |
| Issue number | 6 |
| DOIs | |
| State | Published - Jun 1 2020 |
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 Award Nos. DE-FC02-04ER54698 (DIII-D), DE-AC52-07NA27344 (LLNL), DE-AC02-09CH11466 (PPPL), DE-AC05-00OR22725 (ORNL), and DE-NA0003525 (SNL) and LDRD Project No. 17-ERD-020. This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
| Funders | Funder number |
|---|---|
| DOE Office of Science | DE-FC02-04ER54698, DE-AC52-07NA27344 |
| U.S. Department of Energy | |
| Office of Science | |
| Fusion Energy Sciences | |
| Lawrence Livermore National Laboratory | DE-AC02-09CH11466 |
| Oak Ridge National Laboratory | DE-NA0003525 |
| Laboratory Directed Research and Development | 17-ERD-020 |
| Princeton Plasma Physics Laboratory | DE-AC05-00OR22725 |
