Divertor Heat Flux Mitigation in High-Performance H-mode Plasmas in the National Spherical Torus Experiment.
Experiments conducted in high-performance 1.0-1.2 MA 6 MW NBI-heated H-mode plasmas with a high flux expansion radiative divertor in NSTX demonstrate that significant divertor peak heat flux reduction and access to detachment may be facilitated naturally in a highly-shaped spherical torus (ST) configuration. Improved plasma performance with high {beta}{sub p} = 15-25%, a high bootstrap current fraction f{sub BS} = 45-50%, longer plasma pulses, and an H-mode regime with smaller ELMs has been achieved in the lower single null configuration with higher-end elongation 2.2-2.4 and triangularity 0.6-0.8. Divertor peak heat fluxes were reduced from 6-12 MW/m{sup 2} to 0.5-2 MW/m{sup 2} in ELMy H-mode discharges using high magnetic flux expansion and partial detachment of the outer strike point at several D{sub 2} injection rates, while good core confinement and pedestal characteristics were maintained. The partially detached divertor regime was characterized by a 30-60% increase in divertor plasma radiation, a peak heat flux reduction by up to 70%, measured in a 10 cm radial zone, a five-fold increase in divertor neutral pressure, and a significant volume recombination rate increase.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 945737
- Report Number(s):
- LLNL-CONF-407194; TRN: US0901082
- Resource Relation:
- Conference: Presented at: The 22nd IAEA Fusion Energy Conference, Geneva, Switzerland, Oct 13 - Oct 18, 2008
- Country of Publication:
- United States
- Language:
- English
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Divertor heat flux mitigation in high-performance H-mode discharges in the National Spherical Torus Experiment
Divertor heat flux mitigation in the National Spherical Torus Experiment