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A thin boron film has been applied to the DIII-D tokamak plasma facing surfaces to reduce impurity influx, particularly oxygen and carbon. A direct result of this surface modification was the observation of a regime of very high energy confinement, VH-mode, with confinement times from 1.5 to 2 times greater than predicted by the H-mode scaling relation for the same set of parameters. VH-mode discharges are characterised by low ohmic target densities, low edge neutral pressure, and reduced recycling. These conditions have reduced the collisionality in the edge region, producing a higher edge pressure gradient and a significant bootstrap current, up to 30 % of the total current. The edge plasma properties after boronisation are described, including reductions in recycling. In particular, the edge plasma conditions necessary for access to VH-mode are discussed, including the boronisation process and properties of the deposited film.

Additional information

Authors: JACKSON G L ET AL., General Atomics, San Diego (US);WINTER J, Forschungszentrum Jülich GmbH, Institut für Plasmaphysik (DE);MOYER R, University of California in Los Angeles (US);WATKINS J, Sandia National Laboratories (US)
Bibliographic Reference: Article: Journal of Nuclear Materials, Vol. 196-198 (1992) pp. 236-240
Record Number: 199310261 / Last updated on: 1994-11-29
Original language: en
Available languages: en