Preliminary demonstration on JET of an ITER neutron environment-compatible quadrupole mass-spectrometer

•ITER radiation hardness assurance policy was recently revised calling for stricter neutron exposure limits for the electronics in systems critical to plasma operations.•ITER DRGA system requires QMS sensors to be placed near plasma in high radiation environment in port cell.•Adding a novel, si electronics-free, RF-matching circuit on the port cell side removes 15 m earlier cable-length limit allowing QMS electronics to be placed in neutron-free environment.•QMS with the extended 80 m cable solution was shown in the laboratory to even better resolve fusion-relevant mass species than present commercial equivalent used on JET.•This improved performance with extended 80 m cable has been demonstrated on JET in pre-DTE2 plasma operations. Strict limits recently imposed on neutron exposure to electronics for critical diagnostic systems on ITER, the fusion reactor demonstration facility under construction in the south of France, has led to the development of a quadrupole mass spectrometer with an exceptionally long cable. An 80 m cable exceeds the last state-of-the art limit of 15 m, imposed by the normally required proximity of the RF supply to the analyzer, and will allow locating the electronics in a neutron safe environment. This breakthrough, a joint development of ORNL with Hiden Analytical Ltd., was enabled by the use of an intermediate, RF-matching unit, free of silicon-based electronics, and using only vacuum tubes and an air-core transformer, rendering it resilient both to ionizing radiation and to fringing magnetic fields. After successful testing of the prototype unit, both at ORNL and Hiden's laboratories, the unit was installed on the JET tokamak, as part of a multi-sensor, divertor effluent gas analysis system, similar to one also under design for ITER. As such, the prototype will be tested both before and during the next nuclear (D-T) operation of JET, planned for mid-2021. In this paper, the prototype development, laboratory testing and first results from non-nuclear plasma pulse testing on JET are presented. The latter include not only successful detection of fusion fuel cycle and impurity species, but also improved resolution and stability over the state-of-the-art, 15m-cable units on the same analysis station.