Confinement and stability of VH-mode discharges in the DIII-D tokamak
A regime of very high confinement (the VH-mode) has been observed in neutral beam heated deuterium discharges in the DIII-D tokamak with thermal energy confinement times up to about 3.6 times that predicted by the ITER-89P L-mode scaling and twice that predicted by ELM-free H-mode thermal confinement scalings. This high confinement has led to increased plasma performance. Detailed transport analysis shows a correspondence between the large decrease in thermal diffusivity in the region with electron density values between 0.75 and 0.9 and the development of a strong shear in the radial electric field in the same region. This suggests that stabilisation of turbulence by sheared E x B flow is responsible for the improved confinement in VH-mode. A substantial fraction of the edge plasma entering the second regime of stability may also contribute to the increase in confinement. The duration of the VH-mode phase has been lengthened by feedback controlling the input power to limit plasma beta.
Bibliographic Reference: Article: 14th International Conference on Plasma Physics and Controlled Nuclear Fusion Research : Proceedings (1993) pp. 167-180
Record Number: 199411255 / Last updated on: 1994-11-25
Original language: en
Available languages: en