Increased divertor exhaust by electrical bias in DIII-D

The particle exhaust rate of the DIII-D tokamak divertor cryopump system was investigated as a function of gas-puff-regulated core plasma line-averaged density, divertor electrical bias potential and position of the divertor strike point with respect to the pump entrance aperture. The experiment was done with rapidly ELMing H mode plasmas. Divertor bias approximately doubled the maximum achievable exhaust rate and also reduced its sensitivity to the strike point position. The achievable exhaust rate varied roughly as the third power of the core plasma density.