State of the art of nuclear diagnostics for fusion reactors

Nuclear fusion research is one of the most prominent fields set to revolutionize the energy market in the medium-long term period. Recent scientific achievements, such as the ones obtained at JET [1] and NIF [2], have renewed public and private interest in this topic, sparking the creation of numerous new projects and reactor concepts. Nuclear diagnostics are an essential tool to assess any deuterium-tritium machine performance. Absolute neutron counting is the gold standard technique to measure fusion power. Neutron emission spectroscopy grants access to the fuel ion physics providing information on the fuel ion temperature and energy distribution, the fuel ion ratio and the thermal to non-thermal neutron fraction. Gamma-ray and hard X-ray spectroscopy are the most direct way to obtain information on the fast particle energy distribution and their interaction with the plasma. Fusion nuclear diagnostics need to be carefully designed to operate in extreme cenarios, both in terms of operational capabilities (energy range, energy resolution, counting rate potential, etc.) and in terms of robustness in the harsh environment of a nuclear reactor. In this work, we present the state of the art for nuclear measurements in fusion experiments and we discuss possible solutions for the next-generation reactors.