Preparation of the Wisconsin In-Situ Penning (WISP) Gauge for the SAS divertor at DIII-D

The Wisconsin In-Situ Penning (WISP) gauge is a neutral pressure diagnostic developed at the UW-Madison to measure partial pressures in tokamak divertors. Augmented with spectroscopy, the WISP can determine the fractional neutral pressures of recycling impurities, including hydrogen, helium, neon and nitrogen. The in-situ design allows operation within the tokamak toroidal field behind the divertor baffle, substantially reducing neutral transport latency that determines the timescales of ex-vessel gauges. The WISP is designed to operate above 1 mTorr; higher total pressure than most other such gauges. It meets the criteria to survive the bake and the measurement requirements of the Small Angle Slot (SAS) divertor. It has recently been tested to diagnose pressures to 50 mTorr, with additional improvement under development. Qualifying work on an array of photomultiplier tubes (PMTs) and digitizer is also underway for the installation in DIII-D later this year. The WISP represents a significant advance to aid divertor neutral density measurements in high-pressure, impurity-containing regions behind the SAS divertor tiles and adds a capability to characterize local impurity concentrations in seeded detachment experiments.