Behavior of hydrogen in ion sources with hot filaments at very low pressures

Experiments designed to establish the approximate magnitudes of the physical processes occurring in ion sources with hot filaments at pressures of hydrogen near 10 −11 Torr are described. The objective has been to provide the user of such ion sources with a dynamic description of their behavior as measuring instruments for very low pressures of hydrogen. The measurements were carried out in ultrahigh vacuum apparatus of conventional design near background conditions. It was found that behavior was dominated by a surface phase of hydrogen on the walls and on the electron collector. This surface phase is in quasi-equilibrium with the gas phase and contains orders of magnitude more hydrogen than the gas phase. This large reservoir of hydrogen is very sensitive to small thermal changes. Electron bombardment of the electron collector of the ion source generates a current identified as protons, which is modulated in the modulated Bayard–Alpert gauge as if it were a true ion current from the gas phase.