Discharge cleaning on Tokamak Fusion Test Reactor after boronization

• Published in: Journal of vacuum science & technology. A, Vacuum, surfaces, and films Vol. 9; no. 5; pp. 2713 - 2715
• Main Authors: Mueller, D., LaMarche, P. H., Bell, M. G., Blanchard, W., Bush, C. E., Gentile, C., Hawryluk, R. J., Hill, K. W., Janos, A. C., Jobes, F. C., Owens, D. K., Pearson, G., Schivell, J., Ulrickson, M. A., Vannoy, C., Wong, K. L., Dylla, H. F.
• Format: Journal Article
• Language: English
• Published: Melville, NY American Institute of Physics 01-09-1991
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 700201 - Fusion Power Plant Technology- Blanket Engineering; BORON; CLEANING; CLOSED PLASMA DEVICES; DEPOSITION; ELECTRIC DISCHARGES; ELEMENTS; Exact sciences and technology; GLOW DISCHARGES; LIMITERS; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; SEMIMETALS; TFTR TOKAMAK; THERMONUCLEAR DEVICES; TOKAMAK DEVICES; TFTR TOKAMAK; GLOW DISCHARGES; LIMITERS; BORON; DEPOSITION; CLEANING; Tokamak; Temperature; Cleaning; Experimental study; Electric discharge; Current carrying plasma
• ISSN: 0734-2101; 1520-8559
• DOI: 10.1116/1.577230

At the beginning of the 1990 Tokamak Fusion Test Reactor (TFTR) experimental run, after replacement of POCO‐AXF‐5Q graphite tiles on the midplane of the bumper limiter by carbon fiber composite (CFC) tiles and prior to any pulse discharge cleaning (PDC), boronization was performed. Boronization is the deposition of a layer of boron and carbon on the vacuum vessel inner surface by a glow discharge in a diborane, methane, and helium mixture. The amount of discharge cleaning required after boronization was substantially reduced compared to that which was needed after previous openings when boronization was not done. Previously, after a major shutdown, about 105 low current (∼20 kA) Taylor discharge cleaning (TDC) pulses were required before high current (∼400 kA) aggressive pulse discharge cleaning (PDC) pulses could be performed successfully. Aggressive PDC is used to heat the limiters from the vessel bakeout temperature of 150 to 250 °C for a period of several hours. Heating the limiters is important to increase the rate at which water is removed from the carbon limiter tiles. After boronization, the number of required TDC pulses was reduced to <5000. The number of aggressive PDC pulses required was approximately unchanged.