Development of Liquid-nitrogen-cooled Gas Target System

Experiments with radioactive isotope (RI) beams using direct nuclear reactions in inverse kinematics are at the forefront of nuclear physics research to study the structure of short-lived, weakly bound nuclei. Due to the relatively low intensity of RI beams, it is essential to use pure and dense targets to increase luminosity. Commonly used high-purity light nuclear targets include H₂, D₂, and ^3,4He gases, which have low densities at room temperature and pressure. To overcome this limitation, the Institute of Modern Physics, Chinese Academy of Sciences, in collaboration with partner teams, has developed a liquid-nitrogen-cooled, low-temperature gas target system that significantly increases gas density by lowering temperature and increasing pressure. This paper describes its design, operating principle, and offline measurement results. After cooling by liquid nitrogen, the areal density of the target reaches 3.3 mg/cm² with ⁴He gas at 0.2 MPa, eight times higher than at room temperature and pressure. The system operates stably and meets the requirements of RI beam experiments, providing a robust technical platform for RI-beam experiments with gas targets.