1.4 T Test rig for neutral gas pressure gauges testing in magnetic confinement fusion

Abstract Monitoring neutral gas is important for the safe and efficient operation of fusion power plants. A neutral gas pressure gauge (NGPG) is a diagnostic tool developed for this purpose, with ongoing advancements in materials and geometries. In this publication, we present a novel, compact, and cost-effective test rig designed to address the lack of accessible continuous high-field testing facilities. The test rig consists of a Halbach array of permanent magnets generating 1.4 T at the gauge position. To enable thermionic electron emission, the NGPG cathode is heated to temperatures exceeding 1700 K. This localised heat source poses a thermal risk to the Halbach array, which must remain below 80 ∘ C to avoid permanent demagnetisation. The NGPG with a LaB 6 cathode was operated continuously for 7 hours in ultra-high vacuum (UHV, 10 −8 mbar), with Halbach magnet reaching only 39.6 ∘ C. A thermal model was developed, predicting a magnet steady-state temperature of 47.1 ∘ C reached after 45.3 h of continuous operation. Additionally, the risk of cathode poisoning from adhesive outgassing was assessed by externally heating the vessel. Quantitative mass spectrometry confirmed that the residual gas composition remained dominated by water vapour (54.1%) and CO 2 (3.6%), with adhesive decomposition products present only in traces. These results demonstrate that the test rig provides a robust platform for the long-term characterisation of fusion diagnostics.