A long-term stable cold-cathode gauge for the special use in insulating vacuum systems of cryostats in superconducting accelerators

The pressure conditions in insulation vacuum systems of superconducting accelerator rings or nuclear research plants is often controlled and monitored by cold-cathode gauges (hereafter CCGs). However, due to high outgassing rates of the super insulation material foils (MLI) normally used for thermal insulation, the residual gas atmosphere is dominated by high portions of hydrocarbons. If a CCG is operated in such a hydrocarbonous gas atmosphere, its mean useful life-time is substantially limited by a contamination of the gauge head. Consequently, the pressure reading of the gauge becomes erroneous and unreliable [1-3]. At the worst, the gauge can completely fail. To increase the useful operating-time of a CCG we developed an improved cold-cathode gauge of inverted magnetron-type which was specially designed for the long-term operation at high pressures or/and in gas atmospheres with high contents of hydrocarbons. Basic Concept for a CCG with lowcontamination rate In order to increase the useful life-time of a coldcathode gauge one has to avoid the entrance of hydrocarbonous gases into the measuring cell as far as possible. As successfully demonstrated by Haefer [4], this can be easily realized by the means of an ion baffle using a magnetically confined cold-cathode discharge. In such an ion baffle hydrocarbonous gas components will be effectively cracked due to polymerization reactions. Thus, it is obvious to integrate such an ion baffle into a classical coldcathode gauge structure.