Modulating ion current pressure gauge

A remote pressure measurement system suitable for ultra-high vacuum in a very severe noise environment, such as found in high energy accelerators, is reported. The pressure in a beam pipe of the 12 GeV proton synchrotron at the National Laboratory for High Energy Physics has been measured with high accuracy by a newly developed hot-cathode extractor type ionization gauge, here called the modulating ion current gauge. The output signal from the gauge head was sent to the synchrotron subcontrol room by a 120 m long cable and the measurement was carried out with full beam in the synchrotron. The miniaturized gauge head has a hemispherical mesh anode and a cylindrical electrode between the ionization region and the ion-collector to modulate the ion current. The modulated signal is sent to an amplifier via a double shielded coaxial cable and after amplification is detected with a phase sensitive detector. This new gauge can reject externally induced noise. The effects both of ions desorbed by electron-impact from the anode and of X-ray photocurrents from the ion-collector can also be avoided.