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 Pam
3 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.
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