Hydrogen gas re-emission from beam target bombarded by intense neutral hydrogen beam of 75–100 keV, 1.4 MW at the prototype JT-60 injector

A beam target made of oxygen-free copper with 0.2% silver added was bombarded by a intense neutral hydrogen beam of 75–100 keV, 1.4 MW for 10 s at the prototype injector unit for JT-60 neutral beam injection. Hydrogen gas which was re-emitted from the beam target at the time constant of about 1 s was evacuated by a cryopump with a pumping speed of 960 m 3 /s. We compared the re-emitted hydrogen gas flow rate from the beam target with the number of particles in the hydrogen beam and concluded that the hydrogen gas re-emission coefficient is almost 1.