The design and operation of a new extractor gauge for UHV pressure measurements

The design of a new extractor gauge is described for ultra high vacuum pressure measurements. which employs a separate extractor electrode external to the grid. The advantages to be gained by the use of this system, the importance of providing an adequate ion extraction field and also of preventing the flow of electrons into the collector region, are discussed. A method is described of reducing the effect on the residual current of X-rays reflected onto the collector. This allows a residual current of 10^?14 A, at 1 mA electron current, to be achieved. For a gauge sensitivity of 10 torr^?1 this is equivalent to a residual pressure of 1 × 10^?12 torr. The addition of a modulator has been found to give a high modulation factor of 0.95 which should enable the low pressure limit to be extended to below 10^?14 torr.