Neutron measurements from the preliminary tritium experiment at JET (invited)

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Abstract
A comprehensive range of neutron diagnostics has been installed on the Joint European Torus (JET) for studying deuterium plasma discharges; measurements are made for the 2.5‐MeV neutrons emitted from d–d fusion reactions and for the 14‐MeV neutrons from t–d burn‐up reactions undergone by the 1.0‐MeV tritons emitted in the d–d reactions. The time‐resolved 2.5‐MeV neutron emission is recorded with fission chambers, while the very low intensity 14‐MeV neutron emission is recorded with silicon diodes. Absolute calibrations of these measurements are obtained by application of activation techniques. A 19‐channel neutron profile monitor provides emissivity profiles for both 2.5‐ and 14‐MeV neutrons independently. Finally, 2.5‐MeV neutron energy spectra are recorded with a time‐of‐flight spectrometer. The recently performed preliminary tritium experiment (PTE) has provided a unique opportunity to test the performance of these neutron diagnostics with deuterium–tritium plasmas, although the time scale from proposal to completion was too short to permit the installation of dedicated instrumentation for the highly intense 14‐MeV neutron fluxes. Such instrumentation will be provided for the final, active, phase of JET operation. This presentation will concentrate on the performance of the existing diagnostics during the PTE and will indicate some of the lessons that have been learned regarding neutron measurements for future deuterium–tritium discharges.