Neutron emission spectroscopy studies of fusion plasmas of deuterium-tritium in tokamaks

Abstract: Neutron emission spectroscopy measurements were performed at the Joint European Torus(JET) to study fusion plasmas of deuterium-tritium. The instrument used, the magnetic protonrecoil (MPR) neutron spectrometer, was designed and optimised for plasmas of high fusionpower (PF). It has been successfully operated at the world record level of PF =16 MW attainedat JET. This resulted in a range of new plasma diagnostic observations whose quality and scopewould increase even further with higher PF values. Indeed, the MPR is a prototype for the diagnosis of plasmas where thermonuclear ignition is reached (PF≈1 GW), as is the aim of the next step tokamak.This thesis describes the principles of the MPR neutron spectrometer as well as the set-up ofthe experiment at JET. The performance and diagnostic capabilities are illustrated based on theresults obtained. Particular emphasis is given to the focal plane detector of the MPR and to itsmonitoring system which was a direct result of this thesis work. A special study was also doneto quantify how the average thermal motion of the ions in the plasma affects the neutronemission spectrum compared to their collective motion due to plasma rotation. The analysis ofthe MPR data was focused on plasmas with radio frequency (RF) heating. To this end, a newanalysis model was developed to derive information on the heated ion population. For instance,it is shown how the RF perturbs the thermal equilibrium of the fuel ion population which isapproximately described as a triple temperature plasma state. The results and methodspresented are new contributions to the field of fusion plasma diagnostics, and new insight hasbeen provided on the plasma response to RF heating.