Systematic spectral features in the neutron emission from NB heated JET DT plasmas

Neutron emission spectroscopy (NES) has been used at JET to study deuteriumtritium discharges heated with neutral beam (NB) injection of tritium and deuterium at energies of 150 keV and 75 keV, respectively. The measurements were performed using the magnetic proton recoil neutron spectrometer and the data analysed with several contributing spectral components. The analysis model considers neutrons from reactions involving high-energy NB ions in (co and counter) passing and trapped orbits and NB ions slowed down to epithermal energies besides ion reactions within the thermal bulk. This study was undertaken to explore the level of fuel ion kinetic information that can be obtained for different NB heating scenarios. Time dependent information was extracted to study how the plasma response to NIB injection is manifested in the neutron emission for apparent quiescent periods, during spontaneous plasma instabilities (such as sawteeth) and as a result of intentional changes of the plasma conditions such as the NB injection. The discharges for this study were selected to explore the systematic features that neutron emission spectra display for NB heated discharges and the possibility to interpret them in terms of the underlying kinetic state of the fuel ions. The results obtained on the ion temperature, the toroidal rotation and the supra-thermal fraction of the total neutron yield are compared with those of charge exchange recombination spectroscopy and, in some cases, with plasma equilibrium model calculations. A phenomenological analysis of the results is performed from studies of systematics with the object of exploring the uses of the NES diagnostic and their dependence on data quality.