Investigation of physical processes limiting plasma density in H-mode on DIII-D
- General Atomics, San Diego, CA (United States)
- Oak Ridge National Lab., TN (United States); and others
A series of experiments was conducted on the DIII-D tokamak to investigate the physical processes which limit density in high confinement mode (H-mode) discharges. The typical H-mode to low confinement mode (L-mode) transition limit at high density near the empirical Greenwald density limit was avoided by divertor pumping, which reduced divertor neutral pressure and prevented formation of a high density, intense radiation zone (MARFE) near the X-point. It was determined that the density decay time after pellet injection was independent of density relative to the Greenwald limit and increased non-linearly with the plasma current. Magnetohydrodynamic (MHD) activity in pellet-fueled plasmas was observed at all power levels, and often caused unacceptable confinement degradation, except when the neutral beam injected (NBI) power was {le} 3 MW. Formation of MARFEs on closed field lines was avoided with low safety factor (q) operation but was observed at high q, qualitatively consistent with theory. By using pellet fueling and optimizing discharge parameters to avoid each of these limits, an operational space was accessed in which density {approximately} 1.5 {times} Greenwald limit was achieved for 600 ms, and good H-mode confinement was maintained for 300 ms of the density flattop. More significantly, the density was successfully increased to the limit where a central radiative collapse was observed, the most fundamental density limit in tokamaks.
- Research Organization:
- General Atomics, San Diego, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Pennsylvania State Univ., University Park, PA (United States). Coll. of Engineering; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (United States)
- DOE Contract Number:
- AC03-89ER51114; AC05-96OR22464; AC04-94AL85000; FG05-88ER53266; W-7405-ENG-48
- OSTI ID:
- 453507
- Report Number(s):
- GA-A22521; CONF-961102-4; ON: DE97003365; TRN: 97:006741
- Resource Relation:
- Conference: Meeting of the Division of Plasma Physics of the American Physical Society, Denver, CO (United States), 11-15 Nov 1996; Other Information: PBD: Dec 1996
- Country of Publication:
- United States
- Language:
- English
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