Particle Exhaust Characteristics of an In-Vessel Cryopump Used in DIII-D Diverted Plasmas

A particle exhaust scheme, employing a cryocon-densation pump in the outboard divertor region under a baffle, has been installed and operated in the DIII-D tokamak. The cryopump provides toroidally symmetric pumping at a rate of 30 000 to 40 000 ℓ/s for D₂ in the pressure range of 1 to 4 mTorr. Pressures in the 2 to 3 mTorr range are routinely observed under the baffle. This translates to particle exhaust throughputs of ∼100 Torr ℓ/s. The exhaust throughput could be controlled by selecting the position of the plasma strike region with respect to the opening to the baffle chamber. The pump has been used quite effectively for plasma density control.