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Using a hot-cathode-ionization-gauge head with correcting electrode and shield tube which is operated with an automated-pressure-compensating circuit, we have succeeded in reducing pressure-measurement errors caused by an influx of photoelectrons flowing into the gauge head in a synchrotron radiation environment. In the development of this gauge system without the shield tube, it was found that a basic ion current generated around the correcting electrode by emission from the gauge filament, was proportional to the product of emission current detected with a grid (+185 V as the same voltage of the grid of the gauge head) of the correcting electrode and pressure, like an ion current detected with a collector of a hot-cathode-ionization gauge head. It was also found that the gauge system could reduce pressure-measurement errors caused by x-ray currents, using detected currents with the correcting electrode and calculated basic ion currents. When charged particles from an external environment scarcely flowed into the gauge head, currents detected with the correcting electrode were measured precisely in a pressure range from 10-5 Pa to 10-8 Pa, and an emission current detected with the grid was also measured as 380 µA, corresponding to 9.5% of the normal emission current of the gauge head. When the gauge head was mounted on nipples, currents detected with the correcting electrode were also measured. The emission current detected with the grid of the correcting electrode was also measured as about 50 µA. As these results, the differences between these detected currents and the calculated basic ion currents using the measured emission currents of 380 µA and 50 µA, obviously showed the forward x-ray current, and the whole sum of forward and reverse x-ray currents, in the pressure range of 10-7 Pa, respectively. |