Operation of DIII-D with all-graphite walls
- General Atomics, San Diego, California 92186-9784 (United States)
Recently, additional graphite coverage has been installed in the DIII-D tokamak, increasing the graphite tile coverage from 45% to [similar to]90% (limited only by openings for ports). Due to a problem with copper impurity bursts during tokamak discharges, copper foam sheets between the graphite tiles and the Inconel wall have been replaced with Grafoil gaskets (a compressible graphite material), which further increases the surface area of the graphite inside the DIII-D torus. Although additional graphite has the potential for improving DIII-D performance, if not properly conditioned it can also degrade tokamak discharges by contributing to increased low [ital Z] impurity influx (C and O) and higher particle fueling (D). To address these concerns, improvements were implemented both in tile preparation and wall conditioning techniques. All previously installed tiles were grit blasted with boron--carbide grit to remove codeposited metal impurities and all tiles were outgassed to 1000 [degree]C prior to installation. The only conditioning techniques used were baking and helium conditioning (glow and Taylor discharge cleaning) to avoid producing loosely bound carbon. Previously, H[sub 2] or D[sub 2] Taylor discharge cleaning was used extensively during the vent recovery phase. The glow discharge system used for wall conditioning was modified to include a large area electrode (0.32 m[sup 2]). Recovery from the recent 7 month machine opening was extremely rapid with improved modes of energy confinement (H-mode) transitions observed on the fourteenth plasma discharge. In addition, very high confinement (VH-mode) discharges were obtained without boronization, which is further indication of the rapid vent recovery. Lower recycling/lower fueling efficiency was also observed during operation with all-graphite walls. We will also discuss the use of neon and argon glow, and qualification of the new graphite, including outgassing tests of the Grafoil material.
- DOE Contract Number:
- AC03-89ER51114
- OSTI ID:
- 7171156
- Journal Information:
- Journal of Vacuum Science and Technology, A (Vacuum, Surfaces and Films); (United States), Vol. 12:4; ISSN 0734-2101
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
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THERMONUCLEAR REACTOR WALLS
GRAPHITE
TOKAMAK DEVICES
OPERATION
ELECTRIC DISCHARGES
IMPURITIES
SURFACE CLEANING
CARBON
CLEANING
CLOSED PLASMA DEVICES
ELEMENTAL MINERALS
ELEMENTS
MINERALS
NONMETALS
SURFACE FINISHING
THERMONUCLEAR DEVICES
700480* - Fusion Technology- Component Development
Materials Studies- (1992-)