Initial conditioning of the vessel wall and the graphite limiters in DIII-D

Abstract

The Doublet III tokamak has been rebuilt as the DIII-D, to accommodate large cross-section ( a = 0.67 m), highly elongated ( b a ≳ 2 ) plasmas with either a dee-shaped limiter configuration or a single null, poloidal divertor. The new vacuum vessel has been conditioned by a combination of 400°C baking, Taylor pulsed discharge cleaning (TDC), and rf-assisted glow cleaning (RGC). Tokamak operation began in February 1986 with the attainment of an 0.5 MA discharge on the first day plasmas were attempted. Rapid achievement of high current ( I ≥ 2.0 MA) tokamak discharges in the DIII-D device underscores the importance of high temperature bakeout in shortening the initial cleanup period for a vessel with large amounts of graphitic armor.