Synergetic RF and NB heating effects in JET DT plasmas studied with neutron emission spectroscopy

Neutron emission spectroscopy diagnostic has been used to study plasmas produced at JET during the main deuterium-tritium experimental campaign (DTE1). The plasmas were subjected to radio frequency (RF) and neutral beam (NB) heating in different combinations during periods of individual discharges. Similar discharges with different heating combinations were also compared. This paper deals with the possibility of observing direct evidence of synergetic coupling of the ion cyclotron resonance frequency of the RF power to the fast ions from the NB injection. The key signature of such an effect is the high-energy tail in the spectrum of the neutron emission from plasmas subjected to either NB or RF or both simultaneously. Four discharges of the DTE1 campaign were identified as most suitable to search for the synergetic effects including NB(d) and NB(t) heated discharges with RF coupled to the second harmonic resonance of d and t ions. The measured spectra were analysed with up to four components and interpreted in terms of underlying velocity components of the ions responsible for the neutron emission. The results of the analysis are presented and studied from the aspect of finding effects of the application of NB and RF power injection, which go beyond being merely superpositional. Enhanced effects of simultaneous injection are found which are ascribed as synergetic. The strength of the synergetic effect is found to vary depending on the plasma parameters at hand, but this needs further studies to shed light on the underlying physics of the synergetic NB + RF heating effects on the plasma.