Residual currents detected with a correcting electrode in a modified Bayard-Alpert hot-cathode-ionization gauge.

A nude-type hot-cathode-ionization-gauge head with correcting electrode and shield tube, succeeded in reducing practical pressure-measurement errors caused by an influx of photoelectrons in a synchrotron radiation environment. In the development of this modified Bayard-Alpert hot-cathode-ionization gauge, experimental results showed that a basic ion current generated around the correcting electrode by emission from the gauge filament, was proportional to an emission current (less than 10% of the normal emission current) detected with a grid of correcting electrode, and that differences between estimated and measured basic ion currents in a pressure range of higher than 10(-8) Pa order meant pressure-independent residual currents detected with the correcting electrode. By using calculated forward x-ray currents, these results also showed that the estimated residual currents with the correcting electrode were mainly caused by x rays from the grid of the hot-cathode-ionization-gauge head and the grid of correcting electrode, and that the x-ray currents with the correcting electrode only caused by x rays from the grid of the hot-cathode-ionization-gauge head were about 11% of the nominal x-ray current of the ionization-gauge head. Furthermore, they may suggest that an expected residual current with the collector can be calculated by using the estimated residual current with the correcting electrode, and that this ionization gauge has an additional function to reduce pressure-measurement errors caused by residual currents, though it is necessary to test the ionization gauge in an extremely high-vacuum environment under the x-ray limit of the gauge.