A measurement of intrinsic outgassing rates in vacuum interrupters

In our paper The effect of magnetron discharge pressure measurement on the actual pressure in vacuum interrupters (ICEPE TS 2015) it was reported that in 2013 vacuum pressures in the 10^-5 mbar range had been measured in a batch of old vacuum interrupters which had been sealed for more than 30 years. This measurement was then repeated in 2015 and found to be in the 10^-6 or 10^-7 mbar range. It was proposed that the discharge involved in the first measurements had the effect of permanently removing gas from the system to very low levels, and that the pressures seen two years later arose from intrinsic outgassing within the interrupters. Now in 2017 our equipment has been improved to measure low pressures better, and the pressures have been measured again after this additional two-year period. The new measurements confirm that permanent magnetron pumping occurs, and the new pressures are compatible with what was expected from the outgassing rates measured in 2015. We believe that these results also confirm our hypothesis that each vacuum interrupter has an intrinsic outgassing rate.