In-Vessel Activation Monitors in JET: Modelling and Experiments
Activation studies were performed in JET with new in-vessel activation monitors. Though primarily dedicated to R&D in the challenging issue of lost a diagnostics for ITER which is being addressed at JET with several techniques, these monitors provide for both neutron and charged particle fluence. A set of samples with different orientation with respect to the magnetic field are transported inside the torus by means of a manipulator arm (in contrast with the conventional JET activation system with pneumatic transport system). In this case, radionuclides with longer half-life were selected and ultra-low background gamma-ray measurements were needed. The irradiation was closer to the plasma and this potentially reduces the neutron scattering problem. This approach could also be of interest for ITER where the calibration methods have yet to be developed. The MCNP neutron transport model for JET was modified to include the activation probe and so provide calculations to help assess the new data. The neutron induced activity on the samples are well reproduced by the calculations.