A Mass-Selective Neutral Particle Energy Analyzer with Background Rejection

A mass-discriminating neutral particle spectrometer has been developed for the Rutherford scattering diagnostic at the TEXTOR tokamak. The analyzer is equipped with a momentum preselector and a triple-coincidence time-of-flight detection system providing a rejection capability for background events. Entering neutral particles are stripped by means of a thin carbon foil. Electrons emitted from a second carbon foil are used to give the time-zero signal. Calibration has been performed for hydrogen and helium particles in the energy range from 10 to 90 keV. The energy loss inside the carbon foils, the absolute efficiency, and the resolution of the analyzer have been investigated. The momentum preselector has a bandwidth of +/- 12.5% with respect to its adjustable central momentum. For both hydrogen and helium, the energy resolution is 2.5% for energies above 30 keV. Calculations show that the analyzer can still operate in the highly radiative environments of nuclear fusion devices.