HISTORY AND DEVELOPMENT OF THE UHV HELMER GAUGE AS AN ANALYTIC INSTRUMENT

The development of the Helmer gauge in 1966 traces from work at the Na tional Research Council of Canada, to the University of Illinois, and thence to the Vacuum Research Laboratory at Varian Associates. Key to the design was our study of the Bayard-Alpert structure as an ion beam source, defining the unexpectedly narrow energy dispersion of the ion beam. This allows use of a cylindrical focusing deflector, with the a perture and ion collector at conjugate focal points. The sensitivity o f the Bayard-Alpert gauge is retained. New stainless-steel and Vaclon pump technology was used to obtain pressures in the E-13 torr range, l ow enough to measure an X-ray limit near 1E-14 torr, thus showing that stainless-steel is as good as glass for creating UHV. Following intro duction of a commercial Helmer gauge, the physical study of its proper ties continued in Europe, principally at PTB and CERN, where the desig n was optimized. Modulation of the beam-focusing system provides an ex quisite, diagnostic fingerprint through which residual collector curre nts may be analyzed. (C) 1998 Published by Elsevier Science Ltd. All r ights reserved.