Abstract
Negative triangularity (NT) is a potentially transformative configuration for tokamak-based fusion energy with its high-performance core, edge localized mode (ELM)-free edge, and low-field-side divertors that could readily scale to an integrated reactor solution. Previous NT work on the TCV and DIII-D tokamaks motivated the installation of graphite-tile armor on the low-field-side lower outer wall of DIII-D. A dedicated multiple-week experimental campaign was conducted to qualify the NT scenario for future reactors. During the DIII-D NT campaign, high confinement ( H 98 y , 2 ≳ 1), high current ( q 95 < 3), and high normalized pressure plasmas ( β N > 2.5) were simultaneously attained in strongly NT-shaped discharges with average triangularity δ avg = −0.5 that were stably controlled. Experiments covered a wide range of DIII-D operational space (plasma current, toroidal field, electron density and pressure) and did not trigger an ELM in a single discharge as long as sufficiently strong NT was maintained; in contrast, to other high-performance ELM-suppression scenarios that have narrower operating windows. These strong NT plasmas had a lower outer divertor X-point shape and maintained a non-ELMing edge with an electron temperature pedestal, exceeding that of typical L-mode plasmas. Also, the following was achieved during the campaign: high normalized density ( n e / n GW of at least 1.7), particle confinement comparable to energy confinement with Z eff ∼ 2 , a detached divertor without impurity seeding, and a mantle radiation scenario using extrinsic impurities. These results are promising for a NT fusion pilot plant but further questions on confinement extrapolation and core-edge integration remain, which motivate future NT studies on DIII-D and beyond.
| Original language | English |
|---|---|
| Article number | 105018 |
| Journal | Plasma Physics and Controlled Fusion |
| Volume | 66 |
| Issue number | 10 |
| DOIs | |
| State | Published - Oct 1 2024 |
Funding
This work was supported in part by the US Department of Energy under the following Awards DE-FC02-04ER54698, DE-FG02-04ER54761, DE-SC0022270, DE-FG02-97ER54415, DE-SC0016154, DE-SC0014264, DE-AC52-07NA27344, DE-SC0020287, DE-SC0019352, DE-AC02-09CH11466, DE-AC05-00OR22725, DE-SC0023100, DE-SC0019302, DE-FG02-08ER54999, DE-FG02-99ER54531 and supported by Japan / U. S. Cooperation in Fusion Research and Development. This work has been carried out within the framework of the EUROfusion Consortium, via the Grant Agreement No 10105220 and funded by the Swiss State Secretariat for Education, Research and Innovation (SERI). We would also like to acknowledge the whole DIII-D team who contributed to this successful negative triangularity campaign.
| Funders | Funder number |
|---|---|
| Staatssekretariat für Bildung, Forschung und Innovation | |
| Spine Education and Research Institute | |
| U.S. Department of Energy | DE-FC02-04ER54698, DE-SC0022270, DE-AC52-07NA27344, DE-SC0014264, DE-FG02-97ER54415, DE-SC0019302, DE-SC0019352, DE-AC05-00OR22725, DE-SC0020287, DE-FG02-08ER54999, DE-SC0023100, DE-SC0016154, DE-FG02-04ER54761, DE-AC02-09CH11466, DE-FG02-99ER54531 |
| U.S. Department of Energy | |
| U. S. Cooperation in Fusion Research and Development | 10105220 |
Keywords
- confinement
- negative triangularity
- NT edge
