Design and calibration of the JET time of flight neutral particle analyzer with high noise rejection capability

This paper describes the design and calibration of a time-of-flight neutral particle analyzer used on the Joint European Torus (JET) tokamak in the diagnostics of plasma close to thermonuclear fusion conditions. The 15 channels of the analyzer can select energy and mass of charge exchange neutrals in the energy range from 0.5 to 250 keV. The analyzer has been calibrated for hydrogen, deuterium, and helium atoms. The utilization of the coincidence technique in the measurement of the time of flight of the detected neutrals also permits discrimination of the particle signal from a random background. Thus, the NPA operates successfully in the presence of the high neutron and gamma fluxes that are characteristic of the high-performance fusion plasmas produced in large tokamaks. The calibration data processing, the signal analysis, and the signal-to-noise evaluation are reported in detail.