Analysis of residual gas by high-resolution mass spectrometry during helium glow discharge cleaning in JT-60U

The residual gas analysis has been conducted by high-resolution mass spectrometry in JT-60U in order to investigate the effect of helium glow discharge cleaning (He-GDC). The residual gas analyzer was able to distinguish between D2 and He peaks during He-GDC. Since the He-GDC started, the partial pressure of D2 gas increases with time and reached its highest pressure (3.8 × 10−4 Pa), which was about ten times larger than that before He-GDC. The total amount of D2, which was released during the He-GDC (7 h), was evaluated as 4.4 Pa m3. The pressure of D2 after He-GDC was significantly lower than before He-GDC, which indicates that the He-GDC is effective to remove the deuterium from plasma facing components.