NEUTRAL PRESSURE STUDIES WITH A FAST IONIZATION GAUGE IN THE DIVERTOR REGION OF THE DIII-D TOKAMAK

An ionization gauge, specially designed to operate in the high magnetic fields of present-day tokamaks (1-6 T) and with electronics designed for fast time response and high noise rejection, was installed and operated in the new pumping plenum in the divertor region of DIII-D. This plenum, formed by a toroidally symmetric baffle, is used to compress neutrals to high pressures (> 1 mTorr) to allow for high particle removal rates when a pump is added inside the plenum. Pressures of 2-20 mTorr were measured with the fast gauge under the baffle, compared to less than 1 mTorr measured by a similar gauge also installed in the divertor but outside the baffle. A detailed description of the fast gauge, its operation, and its calibration is provided.