The role of the radial electric field in confinement and transport in H-mode and VH-mode discharges in the DIII-D tokamak
- General Atomics, San Diego, CA (United States)
- Univ. of California, Los Angeles, CA (United States)
Measurements of the radial electric field, E{sub r}, with high spatial and high time resolution in H-mode and VH-mode discharges in the DIII-D tokamak have revealed the significant influence of the shear in E{sub r} on confinement and transport in these discharges. These measurements are made using the DIII-D Charge Exchange Recombination (CER) System. At the L-H transition in DIII-D plasmas, a negative well-like E{sub r} profile develops just within the magnetic separatrix. A region of shear in E{sub r} results, which extends 1 to 2 cm into the plasma from the separatrix. At the transition, this region of sheared E{sub r} exhibits the greatest increase in impurity ion poloidal rotation velocity and the greatest reduction in plasma fluctuations. A transport barrier is formed in this same region of E {times} B velocity shear as is signified by large increases in the observed gradients of the ion temperature, the carbon density, the electron temperature and electron density. The development of the region of sheared E{sub r}, the increase in impurity ion poloidal rotation, the reduction in plasma turbulence, and the transport barrier all occur simultaneously at the L-H transition. Measurements of the radial electric field, plasma turbulence, thermal transport, and energy confinement have been performed for a wide range of plasma conditions and configurations. The results support the supposition that the progression of improving confinement at the L-H transition, into the H-mode and then into the VH-mode can be explained by the hypothesis of the suppression of plasma turbulence by the increasing penetration of the region of sheared E {times} B velocity into the plasma interior.
- Research Organization:
- General Atomics, San Diego, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC03-89ER51114
- OSTI ID:
- 10194474
- Report Number(s):
- GA-A--21415; CONF-9308183--3; ON: DE94002746
- Country of Publication:
- United States
- Language:
- English
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