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D. L. Rudakov,
J. A. Boedo,
J. H. Yu,
N. H. Brooks,
M. E. Fenstermacher,
M. Groth,
E. M. Hollmann,
C. J. Lasnier,
A. G. McLean,
R. A. Moyer,
P. C. Stangeby,
G. R. Tynan,
W. R. Wampler,
J. G. Watkins,
W. P. West,
C. P. C. Wong, R. J. Bastasz,
D. Buchenauer,
J. Whaley
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ABSTRACT: Erosion of the main chamber plasma-facing components is of concern for ITER. Plasma interaction with the outboard chamber wall is studied in DIII-D using Langmuir probes and optical diagnostics. Fast camera data shows that edge localized modes (ELMs) feature helical filamentary structures propagating towards the outboard wall. Upon reaching the wall, filaments result in regions of local intense plasma-material interaction (PMI) where peak incident particle and heat fluxes are up to two orders of magnitude higher than those between ELMs. In low density/collisionality H-mode discharges, PMI at the outboard wall is almost entirely due to ELMs. A moderate change of the gap between the separatrix and the outer wall strongly affects PMI intensity at the wall. Material samples exposed near the outboard wall showed net carbon deposition in high-density discharges (near the Greenwald limit) and tendency towards net erosion in lower density discharges (similar to 0.45 of the Greenwald limit). (C) 2009 Elsevier B.V. All rights reserved.
Journal of Nuclear Materials. 01/2009; 390-91:785-788.
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D L Rudakov,
W Jacob,
K Krieger,
A Litnovsky,
V Philipps,
W P West,
C P C Wong,
S L Allen, R J Bastasz,
J A Boedo, [......],
M Groth,
E M Hollmann,
C J Lasnier,
A G McLean,
R A Moyer,
P C Stangeby,
W R Wampler,
J G Watkins,
P Wienhold,
J Whaley
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ABSTRACT: A strong effect of a moderately elevated surface temperature on net carbon deposition and deuterium co-deposition in the DIII-D divertor was observed under detached conditions. A graphite DiMES sample with a 2 mm wide, 18 mm deep gap lined with silicon catcher plates was exposed to lower-single-null (LSN) L-mode plasmas first at room temperature, and then pre-heated to 200 °C by a built-in electrical heater. At the elevated temperature, deuterium co-deposition in the gap was reduced by an order of magnitude. At the plasma-facing surface of the pre-heated sample net carbon erosion was measured at a rate of 3 nm s−1, whereas without pre-heating net deposition is normally observed under detachment. In a related experiment three sets of molybdenum mirrors recessed 2 cm below the divertor floor were exposed to identical LSN ELMy H-mode discharges. The first set of mirrors exposed at ambient temperature exhibited net carbon deposition at a rate of up to 3.7 nm s−1 and suffered a significant drop in reflectivity. In contrast, two other mirror sets exposed at elevated temperatures between 90 and 175 °C exhibited practically no carbon deposition and their optical reflectivity in the wavelength range above 500 nm was essentially preserved.
Physica Scripta 03/2007; 2007(T128):29. · 1.20 Impact Factor
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C.P.C. Wong,
D.L. Rudakov,
J.P. Allain, R.J. Bastasz,
N.H. Brooks,
J.N. Brooks,
R.P. Doerner,
T.E. Evans,
A. Hassanein,
W. Jacob,
K. Krieger,
A. Litnovsky,
A.G. McLean,
V. Philipps,
A.Yu. Pigarov,
W.R. Wampler,
J.G. Watkins,
W.P. West,
J. Whaley,
P. Wienhold
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ABSTRACT: The Divertor Materials Evaluation System (DiMES) at General Atomics has successfully advanced the understanding of plasma surface interaction phenomena involving ITER-relevant materials and has been utilized for advanced diagnostic designs in the lower divertor of DIII-D. This paper describes a series of recent successful experiments. These include the study of carbon deposition in gaps and metallic mirrors as a function of temperature, study of dust migration from the divertor, study of methane injection in order to benchmark chemical sputtering diagnostics, and the measurement of charge exchange neutrals with a hydrogen sensor. In concert with the modification of the lower divertor of DIII-D, the DiMES sample vertical location was modified to match the raised divertor floor. The new Mid-plane Material Exposure Sample (MiMES) design will also be presented. MiMES will allow the study and measurement of erosion and redeposition of material at the outboard mid-plane of DIII-D, including effects from convective transport. We will continue to expose relevant materials and advanced diagnostics to different plasma configurations under various operational regimes, including material erosion and redeposition experiments, and gaps and mirror exposures at elevated temperature.
Journal of Nuclear Materials.
