Long and short term trends in vessel conditioning of TFTR

We have investigated trends in the conditioning of the Tokamak Fusion Test Reactor (TFTR) vacuum vessel during the May 1984 to April 1985 run period. The initial conditioning of the vessel, consisting of glow discharge cleaning (GDC) and pulse discharge cleaning (PDC) in concert with a 150°C vessel bakeout, is necessary to assure plasma operation after atmospheric venting. A long term conditioning process, ascribed to limiter conditioning, effectively improves operational conditions during the course of the run. Over several thousand high power plasma discharges, the improvement was documented by using standard parameter (fiducial) plasma discharges. Several techniques demonstrated short term improvements in vessel conditioning during this time period, including: Cr gettering and programming the plasma position relative to the limiter contact area.