Neutral gas pressure gauges in magnetic confinement fusion: From ASDEX Upgrade/W7-X to ITER/SPARC and beyond (invited)

The neutral gas pressure at the plasma boundary is crucial for validating physics-based plasma models and for real-time fueling and exhaust control in magnetic confinement fusion devices. Specialized linear hot cathode ionization gauges, the so-called ASDEX-type gauges or manometers, provide absolute neutral density measurements with kilohertz temporal resolution in strong magnetic fields and the harsh in-vessel reactor environment. This paper summarizes the learnings and open questions encountered during the operation of pressure gauges at ASDEX Upgrade (AUG) and Wendelstein 7-X (W7-X), as well as our laboratory-led development of ITER manometers, with ongoing deployment on SPARC. We address the operation principle and engineering of these specialized pressure gauges and outline the development history of various sensor head types. In doing so, the focus lies on different electron-emitter concepts, including thoriated tungsten wires used at AUG and indirectly heated emitters, such as LaB6 at W7-X and ZrC, which is foreseen for ITER and SPARC. We present the operation of pressure gauges with a comprehensive overview of the various measurement positions at AUG, W7-X, ITER, and SPARC. This paper concludes with ongoing model- and laboratory-driven developments aimed at ensuring the availability of real-time-capable pressure sensors for future commercial fusion reactors, where reliability, radiation hardness, and lifetime are of the utmost importance.