H-mode and VH-mode Confinement Improvement in D3-D: Investigations of Turbulence, Local Transport, and Active Control of the Shear in the E x B Flow
The hypothesis of stabilization of turbulence by shear in the E x B drift speed successfully predicts the observed turbulence reduction and confinement improvement seen at the L to H transition. This same hypothesis is the best explanation to date for the further confinement improvement seen in the plasma core when the plasma goes from H-mode to VH-mode. Consequently, the most fundamental question for H-mode studies now is: how is the electric field E{sub r} formed? The radial force balance equation relates E{sub r} to the main ion pressure gradient Del P{sub i}, poloidal rotation (nu){sub theta i}, and toroidal rotation (nu){sub phi i}. In the plasma edge, direct measurements show Del P{sub i} and (nu){sub theta i} are the important terms at the L to H transition, with Del P{sub i} being the dominant, negative term throughout most of the H-mode. Since E{sub r} is observed to change prior to the change in Del P{sub i}, the authors infer that main ion rotation, probably (nu){sub theta i}, changes first, triggering the transition. E{sub r} is seen to change prior to the change in fluctuations, consistent with E x B shear causing the change in fluctuations and transport. In the plasma core, E{sub r} is primarily related to (nu){sub phi i}. There is a clear temporal and spatial correlation between the change in E x B shear and the region of local confinement improvement when the plasma goes from H-mode to VH-mode. Direct manipulation of (nu){sub phi i} and E x B shear using the drag produced by a non-axisymmetric magnetic perturbation has produced clear changes in local transport consistent with the E x B shear stabilization hypothesis. The implications of these results for theories of the L to H and H to VH transitions will be discussed.
- Research Organization:
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- OSTI ID:
- 266972
- Report Number(s):
- GA-A-21833; CONF-940933-47; DE-96-004009; NIPS-96-35981; CNN: AC03-89ER51114; FG02-91ER54109; FC03-86ER52126; TRN: 9626039
- Resource Relation:
- Conference: 15. international conference on plasma physics and controlled nuclear fusion research, Madrid (Spain), 26 Sep - 1 Oct 1994; Other Information: PBD: Oct 1994
- Country of Publication:
- United States
- Language:
- English
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