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Investigation of the neoclassical ambipolar electric field in ion-root plasmas on W7-X

Journal Article · · Nuclear Fusion
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  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Max-Planck-Inst. für Plasmaphysik, Greifswald (Germany)
  3. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid (Spain). Lab. Nacional de Fusión
  4. Lab. for Plasma Physics, Brussels (Belgium)
  5. Univ. of Maryland, College Park, MD (United States)
  6. Forschungszentrum Jülich (Germany)
  7. National Inst. for Fusion Science, Toki (Japan)
  8. Auburn Univ., AL (United States)
+ Show Author Affiliations
The role of the radial electric field in high-performance ion-root plasmas on Wendelstein 7-X (W7-X) is examined and compared with neoclassical predictions herein. The W7-X stellarator is the world’s first large-scale optimized stellarator. One of the important targets chosen for optimization during the W7-X design process was the reduction of core neoclassical heat transport. This optimization was targeted for reactor-relevant high-density plasmas with $$T_e ≈ T_i$$ in which the neoclassical ambipolar radial electric field is expected to be negative throughout the plasmas core. Measurements of the core radial electric field $$(E_r)$$ have confirmed that ion-root conditions (negative $$(E_r)$$ in the plasma core) have been achieved in W7-X with high-density plasmas and central ECRH. These measured $$(E_r)$$ profiles agree well with the neoclassical ambipolar $$(E_r)$$ predicted by the code SFINCS. This good agreement provides confidence in the validity of neoclassical calculations in high-density ion-root conditions, and enables initial studies on the role of neoclassical transport in the optimized high-density regime of W7-X. Profile measurements of electron temperature $$(T_e)$$, ion temperature $$(T_i)$$ and electron density $$(n_e)$$ along with approximations for the average value of $$Z$$eff have been used as inputs to the sfincs code to calculate the ambipolar $$E_r$$ profile along with neoclassical ion and electron energy flux profiles $(Q$NCi, $$Q$$NCe$$)$$. Finally the total experimental energy input to the plasma from ECRH heating has been compared to the neoclassical energy fluxes to provide a first estimate for the fraction of transport that can be attributed to neoclassical processes in reactorrelevant high-density ion-root conditions.
Research Organization:
Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
Sponsoring Organization:
European Commission; USDOE
Contributing Organization:
The W7-X Team
Grant/Contract Number:
AC02-09CH11466
OSTI ID:
1595801
Alternate ID(s):
OSTI ID: 1668775
OSTI ID: 23013543
Report Number(s):
2020--_157
Journal Information:
Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 3 Vol. 60; ISSN 0029-5515
Publisher:
IOP ScienceCopyright Statement
Country of Publication:
United States
Language:
English

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