Development of a High-Pressure Chamber for the NνDEx-100 Experiment

摘要: NνDEx (No Neutrino Double Beta Decay Experiment) is a next-generation high-precision experiment searching for neutrinoless double beta decay (0νββ) at the China Jinping Underground Laboratory. It employs high-pressure ⁸²Se-enriched selenium hexafluoride (⁸²SeF₆) gas as the working medium, paired with a Time Projection Chamber (TPC) and an amplification-free Top-metal chip readout system for high-precision detection. Given the high toxicity of SeF₆ gas and strict demands on background suppression and sealing safety, developing an ultra-high-tightness, high-mechanical-strength, low-background high-pressure chamber is critical to the experiment. This paper presents the independently designed, fabricated, and integrated high-pressure chamber for the NνDEx-100 experiment, detailing its structural design, material selection, key component development, precision assembly, and comprehensive performance tests. Using vacuum helium hood leak detection, a leak rate of less than 1.5×10⁻¹⁰ mbar·L/s was achieved for the high-pressure chamber. Long-term pressure-retention tests in a near-isothermal environment confirm no significant pressure drop after temperature and ambient pressure corrections. These studies demonstrate that the high-pressure chamber has stable and reliable static sealing. The chamber reaches international standards in leak tightness, mechanical safety, and low-background performance applicable to rare-event decay facilities. It provides core hardware support for next-generation high-pressure TPC-based 0νββ experiments and a reusable engineering design for applications involving toxic and valuable high-pressure gases in particle and nuclear physics experiments.