  A liquid helium-3 target system was developed for experimental studies of
kaonic atoms and kaonic nuclei at J-PARC. helium-3 gas is liquefied in a heat
exchanger cooled below 3.2 K by decompression of liquid helium-4. 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 helium-3. 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 to obtain also
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 helium-4
decompression, was 0.21 W, and the liquid helium-4 consumption rate was 50
L/day.
