Neutron diagnostics for reactor scale fusion experiments: A review of JET systems

Fusion is preparing for and moving towards reactor scale plasma experiments. The ITER project requires stepping up the capabilities of neutron measurement systems because in a fusion reactor, measurements of neutron yield and of fusion power and power density are essential. Fast neutron measurement systems for fusion applications include neutronux measurement systems, neutron imaging systems and neutron spectrometers. The JET tokamak is the most suitable test bed for the development of these systems due to its plasma parameters and unique tritium operation capability. Existing systems include 2 neutron cameras composed of multi-collimator arrays and which allow the development of more advanced applications such as 2-D neutron imaging for the study of critical physical phenomena. The spectral width of the neutron emission should be a reliable indicator of ion temperature in a reactor grade plasma. Therefore, three types of neutron spectrometers are currently being developed. The different approaches, methods and calibration techniques are summarised. Finally, since the needs for development of robust and proved neutron measurement systems for ITER are increasingly recognised, JET has now started a series of interesting technological developments in variouselds including new radiation hard detectors, new electronics and data acquisition.