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

Version 1

      Publication Details (including relevant citation   information):

      Rev. Sci. Instrum. 75(12), 5152 - 5159 (2004).

      This article is related to H. Saeki's presentation at the 48th   National Symposium of the AVS, San Francisco, U.S.A., 2001.

      PACS:

                                                                                                                                  
            07.30.Dz              Vacuum gauges      
            07.77.Ka              Charged-particle beam sources and detectors      
            29.25.Bx              Electron sources      
            07.07.Mp              Transducers      
            29.20.db              Storage rings and colliders      

      Abstract:

      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 to10−9 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 position of the gauge head was about 0.12 mA (90 eV), which   was 3% of the normal emission current from the gauge filament. In   the pressure range of 10−7 Pa, the   pressure-measurement errors which occur in the ring were   reproduced. During the experiment, the variation of the indicated   emission current was less than 1% of the normal emission current.   With no emission from the gauge filament, negative currents were   detected at the grid and the collector of the gauge from the   external-electron source at the same pressures as in the   simulated experiment. It was found that detected negative current   at the grid of the gauge was 50%–60% of the total-electron-beam   current from the external-electron source and it was confirmed   that the detected negative current at the collector depends on   the kinetic energy of the incident electrons. From these results   and calculations, it was also found that the variation of the   emission of the gauge filament did not cause the   negative-pressure indications at all. Furthermore, it was also   confirmed that the hot-cathode-ionization gauge indicated   abnormally low pressures or negative pressures when the net   current detected at the collector in operation of the gauge was   extremely small or negative, respectively, due to the influx of   many electrons from the external environment. These experiments   were done to simulate operation conditions at the SPring-8   storage ring. In the simulated experiments for abnormally   low-pressure indications, pressure measurements using a   hot-cathode-ionization-gauge head with a correcting electrode and   an automated-pressure-compensating circuit were carried out in   the pressure range from 10−6  to10−8 Pa. It was found that the   compensated pressure indicated the actual pressure within an   error range of±15% for incident   electrons with 20 eV, although the indicated pressure of the   ionization-gauge controller was in a different order than that of   the actual pressure and the error current was less than the order   of10−10 A. In the simulated   experiment for negative-pressure indications, it was found that   the shield tube could reduce incident electrons from the   external-electron source by a factor of about 1/10.

      Address (URL): http://rsi.aip.org/resource/1/rsinak/v75/i12/p5152_s1