The TOFOR spectrometer for 2.5 MeV neutron measurements at JET

Abstract

Neutron emission spectroscopy has been demonstrated to be a powerful plasma diagnostic at tokamaks. This was shown with the magnetic proton recoil spectrometer developed for measurement of the 14 MeV neutron emission from deuterium–tritium (DT) plasmas at the Joint European Torus (JET). For diagnosis of D plasmas, a 2.5 MeV spectrometer is needed with a factor of 100 higher efficiency to maintain the count rate because of the lower neutron emission rate. The time-of-flight (TOF) technique has the right attributes for these measurements. However, previous instruments have not achieved the full potential of the technique, especially, with respect to count rate capability. A TOF spectrometer for optimized rate (TOFOR) has been conceptually defined and is now under design and development for construction and use at JET. The TOFOR design goal is a count rate capability of about 300 kHz which should be attainable in high power D discharges at JET. The TOFOR project is now in a research and development stage where the instrument is being characterized through neutron transport calculations and test experiments. The tests aim to determine the response of the plastic scintillator elements from which TOFOR will be constructed. This contribution will present the TOFOR design principles, the results of the simulations and test measurements, and the steps taken to reach the optimized design.