Wisconsin In Situ Penning (WISP) gauge at DIII-D; installed, commissioned, and first experiments

The Wisconsin In Situ Penning (WISP) gauge is a novel high brightness neutral partial pressure gauge developed at the University of Wisconsin Madison. The WISP gauge probe head design has been customized for use in the DIII-D tokamak. The design adds an MHV connector which improves the ease of installation. The second change grounds the cathode plate to the probe head baseplate and the power supply floats at machine potential. Additionally, filter wheels have been added to the spectroscopic systems so six impurities can be studied: He, Ne, N, Ar, Kr, and Xe. Three WISP gauges are now installed in DIII-D. The first gauge is at the 105^o toroidal angle in the upper pumping plenum just outside the shape volume rise (SVR) divertor pumping gap. The second gauge is also at 105^o under a custom small angle slot (SAS) divertor tile with a channel cut through to the gauge. The final gauge is at 225^o under the shelf in the lower pumping plenum. All three WISP gauges have been tested during DIII-D’s startup period and return a D2 signal similar to other pressure gauges within the tokamak. When time becomes available the gauges will be calibrated. Two upcoming experiments in June should provide ample opportunity to demonstrate the WISP gauges usefulness. The first experiment plans to utilize Nitrogen seeding to study the stability of the radiation front in detachment along the divertor leg; and the second will use Neon and Helium for an impurity and Helium exhaust study.