PROBLEMS IN DETERMINING THE LOWEST MEASURABLE PRESSURE OF THE CASCADESTATIC LENS GAUGE

The cascade static lens gauge (CSL gauge) is a total pressure gauge de veloped for the measurement of extremely high vacuums (XHV). Because t his gauge has a very high sensitivity (S congruent to 10(2) Pa-1), exp erimental determination of its lowest measurable pressure is not easy. In this study, in order to confirm it in a practically obtainable vac uum, the sensitivity was lowered by shortening the ion collector and t he noise was increased by increasing the emission current. Under these conditions, the X-ray photo-current was about 0.0025 pA, and the ''X- ray limit'' of a CSL gauge with a full-length ion collector in standar d working condition was estimated to be about 6 x 10(-12) Pa. The assu mptions made for this estimation and several data on the ions desorbed from the anodes by electron stimulation are also discussed. (C) 1998 Elsevier Science ltd. All rights reserved.