Extreme high vacuum technology for particle accelerators

Abstract

Linearly distributed pumping is highly desirable for Storage Rings to limit the pressure rise due to the outgassing induced by the circulating beams. As a byproduct, linear pumping allows extremely low pressures (down to the 10 -14 Torr range) to be achieved in static vacuum conditions. Non Evaporable Getters (NEGs), in the form either of a strip as adopted for LEP or of a thin film coating, may provide linear pumping in a simple and economic way. Compared to the strip, thin film coatings present the additional benefits of reduced beam-induced and thermal outgassing, larger pumping surface, lower activation temperature and applicability to vacuum chambers of very small aperture. The most recent developments of this technique and the present XHV measuring capabilities will be described and discussed with the help of some examples.

The development of vacuum measurements down to extremely high vacuum – XHV

“…The authors reported that the modified Helmer gauge was able to measure pressure in the 10-12 Pa range (with an electron current of 3 mA an ion current of 10-15 A could be detected). The C. Benvenuti conclusion was "IHG (Improved Helmer Gauge) provides accurate measurements in the 10-14 torr range, but it perturbs the pressure to be measured" probably measuring its own outgassing [72]. This kind of gauge is still used at CERN for XHV measurements.…”