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Neutral Particle Analysers (NPA), operating in tokamaks approaching reactor conditions, must be able to discriminate the signal against a strong random background. This report presents a NPA with noise rejection capability, based on the TOF coincidence technique that has been designed, built, tested and fully calibrated in the Frascati ENEA laboratories, and was installed on JET in mid-1990. The effectiveness of the Time of Flight (TOF) approach to noise rejection is discussed analytically, and experimental evidence from the JET TOF NPA is presented. The advantage in the signal to noise ratio given by the TOF technique relative to other noise suppression methods is analysed, and the absence of significant systematic errors is emphasised. The intrinsic flexibility of an instrument based on TOF mass analysis, and the possibility of performing cross tests, both during calibration and operation on the tokamak, are also discussed. The analyser has already shown, in the first experimental period on JET, its strong random noise rejection capability, with rejection factors in excellent agreement with basic probability theory estimates. Many observations have only been made possible by the analyser noise rejection capability, as, for example, the detailed analysis of sawteeth oscillations, which are clearly visible on the time evolution of coincidence count rates much smaller than the noise count rates induced by neutrons on the individual START and STOP detectors.

Additional information

Authors: BRACCO G, ENEA, Centro Ricerche Energia Frascati, Roma (IT);MOLETI A, ENEA, Centro Ricerche Energia Frascati, Roma (IT);TILIA B, ENEA, Centro Ricerche Energia Frascati, Roma (IT);ZANZA V, ENEA, Centro Ricerche Energia Frascati, Roma (IT);CORTI S, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Paper presented: Diagnostics for Contemporary Fusion Experiments, Varenna (IT), August 28 - September 6, 1991
Availability: Available from (1) as Paper EN 36454 ORA
Record Number: 199111542 / Last updated on: 1994-12-02
Original language: en
Available languages: en