Operational Experience With A Remote Radiation Hard Quadrupole Residual-Gas Analyzer

Commercially available quadrupole mass analysers with the solid state electrometer amplifier and rf generator at the measuring head are not radiation resistant. Therefore an analyser for use at JET had to be developed which is able to accommodate a dose of 10(8) rad without significant degradation. The design combines vacuum tubes, at the quadrupole head, with radiation sensitive components such as semiconductors located at the end of 100 m cables. The prototype analyser has been operated extensively on JET in order to assess its suitability for use during the main tritium phase of JET. The testing has validated the precepts of the design and with small design revisions the performance is acceptable. Significantly, with the remote analyser, it is possible to obtain mass spectra of similar quality to those derived from a conventional Faraday cup quadrupole and to detect partial pressures in the 10(-11) mbar range.