Spontaneous oscillations of some gas species concentration in an UHV apparatus

Continuous oscillations of the pressure of hydrogen and some other gases were observed in an ultra high vacuum (UHV) apparatus. The oscillations arose progressively during experiments with hydrogen permeation through stainless-steel ion-implanted samples, later they occurred in the apparatus without any sample as well. They were observed for a long time, detected with an ionisation gauge and a mass spectrometer, both simultaneously and with each instrument separately. The oscillation period was approximately 20-30 s and the amplitude was some tens of the average partial pressure of the gas.