Outgassing during a plasma disruption in the JT-60 tokamak

A new gauge with a fast time response has been developed for measuring the vacuum pressure of a tokamak fusion device, JT-60. The pressure is measured during and after a hydrogen plasma discharge shot in order to investigate the mechanism of outgassing from the first wall, which is made of graphite. The evacuated gas quantity after a typical disruption is almost equal to or greater than the amount of gas input. After a typical plasma disruption, the amount of gas of ∼40 Pam3 is released within 50 ms. This is probably caused by the heat flux to the first wall due to both the plasma thermal and magnetic energies. It is observed that three-quarters of the gas released returns to the first wall. On the other hand, the evacuated quantity after normal plasma discharge is less than the gas input. (author)