Remote leak detection in the molecular flow regime with ion gauges internal to the vacuum system

Traditionally, leaks in vacuum systems have been located by attaching a gas-species-sensitive detector, usually a helium-sensitive mass spectrometer, and spraying small specific surface areas with a tracer gas. In cases where an internal remote manipulation system exists, such as for a high level of radioactivity or mechanical process manipulation, another method of leak detection suggests itself. A suitable internal remote manipulator can position an ion gauge so as to detect an increase in density due to the directed flux (i.e. wind) emanating from a leak. A simplified theoretical analysis and experimental results are presented. Results of measurements using a Seiko gauge are given, along with leak telescope results. Sensitivity, spatial resolution and scanning rates are presented. Since ion gauges generally operate at pressures in the molecular flow regime, an analysis is carried out to predict the signal expected as a function of leak size and distance. Two leak flux distributions are considered: uniform and cosine law