Development of a cryogenic gas target system for intense radioisotope beam production at CRIB

A cryogenic gas target system was developed for the radioisotope (RI) beam production at CNS Radio Isotope Beam separator (CRIB). Hydrogen gas was cooled to 85–90 K using liquid nitrogen and used as a secondary beam production target having a thickness of 2.3 mg / cm 2 . An intense 7Be beam ( 2 × 10 8 particles per second) was successfully produced using this target. We observed a density-reduction effect at the gas target for high-current primary beams with about 7.5 W heat deposition. One main feature of the target system is forced circulation of the target gas. We have found that the circulation of the target gas at a rate of 55 standard liters per minute (slm) was effective in eliminating the density reduction. The extent to which the forced flow can prevent the density reduction had not been known well. In this work, the relation between the density reduction and the forced circulation rate was quantitatively studied.