Evolution and termination of H-modes in NSTX
- Oak Ridge National Laboratory (ORNL)
- ORNL
The dynamic evolution of the first National SphericalTorus Experiment (NSTX) H-modes will be discussed. The H-modes were obtained in lower-single null divertor discharges with various forms of plasma heating. The exact timing of divertor formation and also the NBI power level affects both whether or not the discharge exhibits ELMs and the duration of the ELM-free phase. ELM-free discharges had energy confinement as high as 120 ms, whereas the few discharges with ELMs had confinement times 50 70 ms. Buildup of a steep edge density gradient and formation of ears on the density profile were observed within a few ms of the L H transition, yielding broader density and pressure profiles. The L H transition was marked by a decrease in edge visible light and simultaneous increase in electron Bernstein wave emission, reflecting a steepening of the edge density gradient. Gas puff imaging of He-I light during the H-mode phase showed rapid formation of a narrow emission layer 2 cmwide in the H-mode phase, which returned within 20 microseconds at termination of the H-mode phase to a broader turbulent emission layer. All of the H-modes were terminated by an MHD reconnection event. The first power threshold (Pth) study showed the neutral beam injection power (Pb) component of Pth to be0.84MW, higher than that predicted by the ITER database scaling.
- Research Organization:
- Oak Ridge National Laboratory (ORNL)
- Sponsoring Organization:
- SC USDOE - Office of Science (SC)
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1081847
- Journal Information:
- Plasma Physics and Controlled Fusion, Journal Name: Plasma Physics and Controlled Fusion Journal Issue: 5A Vol. 44; ISSN 0741-3335
- Country of Publication:
- United States
- Language:
- English
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