The evolution of TOFu : Developing and utilizing neutron time-of-flight spectrometry of deuterium and tritium fusion plasmas at JET

Sammanfattning: Considerable effort has been invested in attempting to generate electricity from the energy released in controlled thermonuclear fusion reactions, with a European fusion research roadmap stretching beyond 2050. Our current endeavors may culminate in a virtually inexhaustible, low-carbon energy source for future generations. Experimental reactors such as the Joint European Torus (JET) and the International Thermonuclear Experimental Reactor (ITER) are stepping stones on the road to demonstrating the viability of fusion energy. Using various diagnostics and simulations, information on the plasma conditions in such experimental reactors can be obtained.In this thesis, the neutron time-of-flight spectrometer TOFOR at JET is used to study the neutron emission spectrum from the JET machine to determine different fusion plasma parameters. The first part of the thesis describes the efforts to upgrade the data acquisition (DAQ) system of TOFOR with a new, fully digital system: TOFu. Data reduction techniques are developed for the new DAQ system, and are shown to increase the signal-to-background ratio significantly. The instrumental response function is improved using the new system by measuring the energy-dependent time resolution and energy thresholds and applying them to the response function. Data analysis routines are developed to generate time-of-flight spectra from the data acquired by the 37 TOFOR sub-detectors.In the second part of the thesis, the data acquired by the new DAQ system is used to perform various physics studies of JET plasmas. We demonstrate the possibility of measuring the fuel ion temperature for Ohmic discharges of pure deuterium plasmas, with a precision that was unattainable with the former DAQ system. Furthermore, during the time of my doctoral studies, two deuterium-tritium experimental campaigns (DTE2 and DTE3) were conducted at JET. In order to contribute to the analysis of these experiments, we developed methods to measure the tritium fuel concentration in the fusion plasma using TOFOR. Also, experiments with pure tritium plasmas gave us the unique opportunity to measure the neutron emission spectrum from the T + T4He + 2n reaction during which we made the first observation in a magnetically confined plasma of the intermediate resonant reaction T + T5He + n.The analysis methods and experimental techniques developed in this thesis may be used in future neutron spectrometry systems, e.g., at ITER where there are plans to build a high-resolution neutron spectrometer (HRNS) consisting of several detection systems, one of which is a TOFOR-like time-of-flight spectrometer.