Impurity neutral partial pressure measurements at DIII-D with the Wisconsin In-Situ Penning (WISP) gauges

Three novel Wisconsin In-Situ Penning (WISP) gauges have been installed on DIII-D and used for impurity measurements of helium, neon, argon, and nitrogen in a range of discharges, providing important information about neutrals in divertors and the far scrape-off layer. The WISP gauge is a high brightness neutral partial pressure gauge developed at the University of Wisconsin Madison. The gauges were commissioned and operated at the end of 2024.

The 2025 campaign offered different experiments which utilized impurity puffing, allowing the WISP gauges to demonstrate the principal purpose of improving neutral impurity measurements over legacy optical penning gauges. Back calibrations in August are still needed to refine the collected data. A focal experiment used WISP gauges to study how RMPs affect impurity confinement in an ITER similar shape.

Data from the gauges will be used to compare impurity transport to the wall in divertors with a range of closure to the core. Results from these measurements are critical for future code validation of impurity transport in the plasma edge, where impurities are the dominant cause of erosion of the first wall armor.

Work supported by US DOE under FC02-04ER54698, DE-SC0020284, DE-AC02-09CH11466, DE‑AC05‑00OR22725, DE‑AC52‑07NA27344, DE‑SC0014264