Monitoring of neutrons in nuclear reactors

Nuclear fusion power is an experimental form of power generation that generates electricity by means of nuclear fusion reactions. In a fusion process, two atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices that produce energy in this way are known as fusion reactors. Fusion occurs in a plasma confined at sufficient temperature and pressure for a sufficient time interval.

To achieve efficient energy production, the fusion plasma needs continuous monitoring and stabilization which in turn requires a comprehensive, multi-parameter insight into the processes taking place inside the core vessel. Fusion plasma diagnostics is an extensive subject itself, and constitutes a large and important part of fusion experiments. Due to the extreme heat, no physical measurement devices can be placed directly inside the plasma. However, since the thermonuclear plasma is a source of electromagnetic and particle radiation, the plasma diagnostics can rely on “out-of-the-core” measurements of the emission, transmission or scattering of particles or electromagnetic radiation. In the most promising of the hydrogen fusion reactions, when a mixture of deuterium and tritium is used, about 80% of fusion energy yield is carried by the neutron. Thus, the number of produced neutrons is a direct measure of the thermonuclear reaction.  As neutrons do not have the electric charge, they can easily escape from the plasma confining  magnetic field and be registered by a diagnostic system. Neutron Flux Monitors (NFM) are thus a fundamental diagnostic sub-system for any fusion reactor. Different types of NFM are available (use link). These systems are based on concepts originally developed for fission reactors and experimental neutron physics. The most established monitoring technology is based on fission chambers which are particular ionization chambers in which the entrance window is made of radioactive materials, allowing amplification of the signal. These systems allow measuring the neutron fluxes emitted by the plasma with high sensitivity and dynamic range which, in combination with spatial emission profile measurements and tomographic methods, allow reconstructing the plasma distribution. On the other hand, the study of the neutron spectrum can provide information on plasma temperature, density and attain information on ion species partaking in or affecting the fusion process. Diamond has been tested for this application, but has strong limitations, in stability as well as size. We aim at validating SiC detectors, in terms of: (i) radiation hardness, (ii) high-resolution spectroscopic real-time measurements of neutrons, (iii) speed, (iv) very large areas (>>1x1cm2) and (v) pixellation.