The return of permanent gas pressure in sealed vacuum interrupters

The vacuum pressure in Vacuum Interrupters (VI) is usually measured by inducing a magnetron discharge inside them. We have previously reported evidence that if this discharge is continued for long enough it causes the gases to be chemically bonded to solid surfaces in the interrupter, resulting in a permanent reduction of pressure. In a small proportion of interrupters however the pressure returns to a stable level similar to the pre-discharge pressure over a period of hours or days. We now report on measurements of this pressure recovery. It was found that with these VI the cycle of pumping and pressure return is repeatable. With this information it may be possible to adapt magnetron testing procedures to distinguish between pressure rise due to return of permanent gas, which will level off, and continuous pressure rise due to internal outgassing.