Fusion product measurements by nuclear diagnostics in the JET Deuterium-Tritium 2 campaign: lessons learnt and implications for ITER

The Deuterium Tritium (DT) Experiment campaign 2 (DTE2) has been successfully carried out at the Joint European Torus. An important goal of the campaign has been the detailed and systematic measurement of fusion born products, benefitting from a preparatory diagnostic upgrade program over the recent years. This talk will present an overview of the measurements, some of the unprecedented opportunities for physics studies they have opened and the challenges that still need to be addressed in preparation for ITER. Fusion products have been measured in a broad range of scenarios primarily by nuclear diagnostics and, for the first time, with an ITER like wall, which allowed testing many of the methods envisaged for the nuclear phase of ITER. High resolution gamma-ray spectroscopy has been demonstrated for the first time in a 50:50 DT plasma. 17 MeV gamma-rays born from fusion reactions between deuterium and tritium have been successfully detected and used to develop a method to determine the fusion power, complementing that based on neutron yield measurements. Slowing down, confined alpha particles with energies in excess of ?1.9 MeV were detected by means of the 4.44 MeV gamma-ray peak that comes from their spontaneous reaction with 9Be impurities. As far as neutron measurements are concerned, chemical vapour deposition diamonds have been used to measure the neutron spectrum on multiple lines of sight (LOS) and complemented more established, single LOS data obtained with the magnetic proton recoil spectrometer. The successful upgrade of the set of Faraday cups and the fast ion loss detector made it possible to detect lost alpha particles, to determine their velocity space and to study their interplay with instabilities. From a more technical viewpoint, DTE2 has also allowed testing some of the reference solutions so far adopted in the design of diagnostics for fusion products at ITER and to learn some lessons. These range from the essential role that attenuators have in enabling gamma-ray measurements, particularly LiH, to the full assessment of the background that pollutes the data for some applications.