Spectroscopic determinations of carbon fluxes, sources, and shielding in the DIII-D divertors

The most important mechanisms for eroding plasma-facing components (PFCs) a nd introducing carbon into tokamak divertors are believed to be physical sp uttering, chemical sputtering, sublimation, and radiation enhance sublimati on (RES). The relative importance of these processes has been investigated by analyzing the spectral emission rates and the effective temperatures of CI, CD, and C-2 under several operating conditions in the DIII-D tokamak [P lasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomi c Energy Agency, Vienna, 1987), Vol. I, p. 159; Proceedings of the 18th IEE E/NPSS Symposium on Fusion Engineering, Albuquerque (Institute of Electrica l and Electronic Engineers, Piscataway, 1999), p. 515]. Discrimination of c hemical sputtering from physical sputtering is accomplished by quantitative ly relating the fraction of CI influxes expected from dissociation of hydro carbons to the measured CD and C-2 influxes. Characteristics of sublimation are studied from carbon test samples heated to surface temperatures exceed ing 2000 K. The shielding efficiency of carbon produced at the divertor tar get is assessed from comparison of fluxes of neutral atoms and ions; approx imately 95% of the primary influx appears to be redeposited before being tr ansported far enough upstream to fuel the core plasma. (C) 2001 American In stitute of Physics.