Recycling and particle control in DIII-D
Particle control of both hydrogen and impurity atoms is important in obtaining reproducible discharges with a low fraction of radiated power in the DIII-D tokamak. The main DIII-D plasma facing components are graphite tiles and Inconel. Hydrogenic species desorbed from graphite during a tokamak discharge can be a major fueling source, especially in unconditioned graphite where these species can saturate the surface regions. In this case the recycling coefficient can exceed unity, leading to an uncontrolled density rise. In addition to removing volatile hydrocarbons and oxygen, DIII-D vessel conditioning efforts have been directed at the reduction of particle fueling from the graphite tiles. Conditioning techniques include: baking to {le} 400{degrees}C, low power pulsed discharge cleaning, and glow discharges in deuterium, helium, neon, or argon. Helium glow wall conditioning, is now routinely performed before every tokamak discharge. The effects of these techniques on hydrogen recycling and impurity influxes will be presented. The Inconel walls, while not generally exposed to high heat fluxes, nevertheless represent a source of metal impurities which can lead to impurity accumulation in the discharge and a high fraction of radiated power, particularly in H-mode discharges at higher plasma currents, I{sub p} > 1.5 MA. To reduce metal influx a thin ({approximately}100 nm) low Z film has been applied on all plasma facing surfaces in DIII-D. The application of the boron film, referred to as boronization has the additional benefit over a carbon film of further reducing the oxygen influx. Following the first boronization in DIII-D a regime of very high confinement (VH-mode) was observed, characterized by low ohmic target density, low Z{sub eff}, and low radiated power.
- Research Organization:
- General Atomics, San Diego, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC03-89ER51114
- OSTI ID:
- 10121980
- Report Number(s):
- GA-A-20743; CONF-911132-20; ON: DE92007944
- Resource Relation:
- Conference: 38. national symposium of the American Vacuum Society,Seattle, WA (United States),11-15 Nov 1991; Other Information: PBD: Nov 1991
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
DOUBLET-3 DEVICE
PLASMA IMPURITIES
GRAPHITE
H-MODE PLASMA CONFINEMENT
FIRST WALL
FUEL CYCLE
THIN FILMS
CARBONIZATION
BORON
CONFINEMENT TIME
EDGE LOCALIZED MODES
700420
700310
700330
PLASMA-FACING COMPONENTS
PLASMA CONFINEMENT
PLASMA KINETICS, TRANSPORT, AND IMPURITIES