Hot-cathode-ionization-gauge system with a self-compensating circuit for errors caused by an external-electron source

A hot-cathode-ionization-gauge system, consisting of a gauge head with a correcting electrode, an automated-pressure-compensating circuit, and a shield tube, succeeded in overcoming two kinds of erroneous pressure indications with hot-cathode-ionization gauges. Several tens of hot-cathode-ionization gauges in the SPring-8 storage ring have indicated abnormally low pressures (of the order from 10−8 to 10−9 Pa) at stored-electron-beam conditions due to an influx of photoelectrons. Some of these gauges, located near photon absorbers, have indicated negative pressures (from −2×10−9 to −2×10−7 Pa). To investigate these pressure-measurement errors, simulated experiments to reproduce the phenomena were carried out using an external-electron source which was located near a hot-cathode-ionization-gauge head. The kinetic energy of incident electrons to the gauge head from the external-electron source was varied from 10 to 90 eV. The maximum total-electron-beam current from the external-electron source at the positi...