Field emission current from surfaces under vacuum and at high field strengths can be reduced by the injection of gas into the evacuated volume. In this paper, the effects of ${\mathrm{H}}_2$, He, ${\mathrm{N}}_2$, and Ar on this “dark” current emitted from a tungsten carbide point cathode for 2 cm gap distance is studied. Exposure to any of these gases at pressures on the order of ${10}^{-3}–{10}^{-2}\mathrm{Pa}$ was found to reduce the emission current by up to 90% with a time constant on the order of $\sim 1\mathrm{minute}$ as compared to the current at ${10}^{-6}\mathrm{Pa}$. The effect was strongly dependent on the gas nature, with Ar and ${\mathrm{N}}_2$ having larger effects at lower pressures than He and ${\mathrm{H}}_2$. The reduction was reversible, with the current increasing to near its original value with a time constant on the order of $\sim 1–10\mathrm{minutes}$ after pumping down. The effect of the gas remained in the absence of electric field, whatever the gas pressure. Mechanisms for these and related phenomena are discussed.

• Received 12 June 2014

DOI:https://doi.org/10.1103/PhysRevSTAB.17.103502

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Published by the American Physical Society