Development of a liquid 3He target for experimental studies of antikaon–nucleon interaction at J-PARC

A liquid 3He target system was developed for experimental studies of kaonic atoms and kaonic nuclei at J-PARC. 3He gas is liquefied in a heat exchanger cooled below 3.2 K by decompression of liquid 4He. To maintain a large acceptance of the cylindrical detector system for decay particles of kaonic nuclei, efficient heat transport between the separate target cell and the main unit is realized using circulation of liquid 3He. To minimize the amount of material, a vacuum vessel containing a carbon fiber reinforced plastic cylinder having an inside diameter of 150 mm and a thickness of 1 mm was produced. A target cell made of pure beryllium and beryllium–aluminum alloy was developed not only to minimize the amount of material but also to obtain high X-ray transmission. During a cooling test, the target cell was kept at 1.3 K at a pressure of 33 mbar. The total estimated heat load to the components including the target cell and heat exchanger cooled by liquid 4He decompression, was 0.21 W, and the liquid 4He consumption rate was 50 L/day.