Developing physics basis for the snowflake divertor in the DIII-D tokamak
- Lawrence Livermore National Lab., Livermore, CA (United States)
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Princeton Univ., Princeton, NJ (United States)
- General Atomics, San Diego, CA (United States)
- Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Here, recent DIII-D results demonstrate that the snowflake (SF) divertor geometry (see standard divertor) enables significant manipulation of divertor heat transport for heat spreading and reduction in attached and radiative divertor regimes, between and during edge localized modes (ELMs), while maintaining good H-mode confinement. Snowflake divertor configurations have been realized in the DIII-D tokamak for several seconds in H-mode discharges with heating power $$P_{\rm NBI} \leqslant 4$$ –5 MW and a range of plasma currents $$I_{\rm p}=0.8-1.2$$ MA. In this work, inter-ELM transport and radiative SF divertor properties are studied. Significant impact of geometric properties on SOL and divertor plasma parameters, including increased poloidal magnetic flux expansion, divertor magnetic field line length and divertor volume, is confirmed. In the SF-minus configuration, heat deposition is affected by the geometry, and peak divertor heat fluxes are significantly reduced. In the SF-plus and near-exact SF configurations, divertor peak heat flux reduction and outer strike point heat flux profile broadening are observed. Inter-ELM sharing of power and particle fluxes between the main and additional snowflake divertor strike points has been demonstrated. The additional strike points typically receive up to 10–15% of total outer divertor power. Measurements of electron pressure and poloidal beta $$\beta_p$$ support the theoretically proposed churning mode that is driven by toroidal curvature and vertical pressure gradient in the weak poloidal field region. A comparison of the 4–4.5 MW NBI-heated H-mode plasmas with radiative SF divertor and the standard radiative divertor (both induced with additional gas puffing) shows a nearly complete power detachment and broader divertor radiated power distribution in the SF, as compared to a partial detachment and peaked localized radiation in the standard divertor. However, insignificant difference in the detachment onset w.r.t. density between the SF and the standard divertor was found. The results complement the initial SF divertor studies conducted in high-power H-mode discharges in the NSTX and DIII-D tokamaks, and, along with snowflake divertor results from TCV and other tokamaks, contribute to the physics basis of the SF divertor as a power exhaust concept for future high power density tokamaks.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); General Atomics, San Diego, CA (United States)
- Sponsoring Organization:
- USDOE
- Grant/Contract Number:
- AC52-07NA27344; FC02-04ER54698
- OSTI ID:
- 1420291
- Alternate ID(s):
- OSTI ID: 1420278
- Report Number(s):
- LLNL-JRNL-730504; TRN: US1801481
- Journal Information:
- Nuclear Fusion, Vol. 58, Issue 3; ISSN 0029-5515
- Publisher:
- IOP ScienceCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Design and simulation of the snowflake divertor control for NSTX–U
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journal | January 2019 |
The effect of the secondary x-point on the scrape-off layer transport in the TCV snowflake minus divertor
|
journal | December 2018 |
Turbulence and flows in the plasma boundary of snowflake magnetic configurations
|
journal | January 2020 |
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