Method to compensate radiation-induced errors in a hot-cathode-ionization gauge with correcting electrode

Abstract

A previous method to compensate radiation-induced errors caused by the synchrotron radiation environment used a hot-cathode-ionization gauge with correcting electrode and shield tube. This compensating method was based on an approximate formula, and the compensated pressure measurement displayed large errors for pressures below ∼10−7 Pa. To overcome this problem, a new method, based on an exact formula, and use of precision electrometers, has now been developed and tested in a simulation experiment with excess electrons. This method reduced the pressure-measurement error to approximately 1% and is not restricted to use in a specific pressure range, even without use of a shield tube, unlike the previous method. The experimental result suggests that the new compensating method can be used in severe synchrotron radiation environments with photoelectrons.

Precise method of compensating radiation-induced errors in a hot-cathode-ionization gauge with correcting electrode

“…10, CE is the proportionality constant for radiation-induced current between the correcting electrode cable and its reference cable, I CErr (A) is the detected current in the reference cable, C is the proportionality constant for radiation-induced current between the collector cable and its reference cable, and I Crr (A) is the detected current in the reference cable, S CE (1/Pa) is the sensitivity of the correcting electrode, shown in Ref. 5. An "emission current" I CEe (A) measured at the grid of the correcting electrode, due to the influx of electrons originating from the external environment and the primary gauge filament, although described by mistake in Ref.…”

“…[7,8] In simulation experiments with excess electrons and with actual synchrotron radiation, the method could displayed the resulting pressure with a pressure measurement error of less than 22 %. [3,4,9] However the method based on an approximate formula was restricted to use in a specific pressure range, related to the influx of photoelectrons, and displayed large errors for pressures below 8 10 -8 Pa. [3,9] Furthermore to solve these problems, a precise method [5] based on an exact formula, was developed without use of the shield tube and the existing vacuum-gauge controller together with the automated-pressure-compensating circuit. In an experiment with excess electrons simulating a synchrotron radiation environment in the SPring-8 storage ring, this precise method without the vacuum-gauge cable could obtain the actual pressure with a pressure-measurement error less than several percent.…”

“…Since then, as a result of various countermeasures employed, such as using u-shaped gauge-port tubes, permanent magnets, lead sheets, and frequently-replaced vacuum-gauge cables, this simple phenomenon has become complicated and the pressure-measurement errors caused by insufficient radiation shields have been amplified. [5] The phenomenon has been well known and observed in many electron storage rings since the 1970s. [6] To overcome this problem, a hot-cathode-ionization-gauge head with correcting electrode [2] was developed and was operated by an existing vacuum-gauge controller together with an automated-pressure-compensating circuit, [3] a shield tube, and a vacuum-gauge cable with long-term resistance to radiation.…”

Thermionic Emitters

“…14.7, measurements of the current due to externally-produced electrons are made at the correcting electrode in an auxilliary gauge which does not contain a thermionic emitter filament, and these measurements, applied to the current measurement from the normal gauge, can be used to make corrections to the measured ion current and calculated pressure. The details of this are dealt with in a recent paper [28], and background information will be found in earlier papers [29][30][31][32][33][34][35]. Figure 14.7 shows the side view of the gauge design and its logic.…”

“…The measurement of I CEe , the external electron current received by the grid (and hence available within the gauge structure for ionization of gases), is also employed to make corrections to the measured ion current in the normal gauge. Reference [28] gives a formula to measure a compensated pressure in this gauge. Figure 14.7 shows the measurements of the uncorrected gauge, BA-S4, compared to measurements of the corrected gauge, BA-S4.…”