This research project centres on advancing data analysis techniques using the Magnetic Proton Recoil Upgrade Neutron Spectrometer (MPRu) for neutron emission spectroscopy during the deuterium tritium experimental campaign (DTE2) at the Joint European Torus (JET). The study aimed to address three pivotal questions, each with implications for optimizing data accuracy, quality, and utility. The first question focused on determining the optimal short-gate settings for the MPRu. Extensive analysis revealed that conventional metrics, such as the Full Width at Half Maximum (FWHM) and spatial positioning of the proton island, were inadequate for precise short-gate configuration. It was concluded that the existing settings, characterized by a +30 offset from the signal onset, proved to be sufficient. This choice was driven by the necessity to distinguish between escape events, shadow events, and the proton island when plotting signals in a 2-D graph, proving effective across all detector channels. Accurate proton counting hinges on the precise assessment of protons within the escape event region, a task complicated by the interference of background events. This study investigated the point at which the accuracy of the escape event region diminishes by comparing the relative count with simulated data. Results demonstrated that higher-energy signals, positioned farther from the background-concentrated origin, yielded more accurate counts. Additionally, a correction factor based on simulated data is suggested for the unaccounted proton signals. The third question explored was the feasibility of modelling the proton island's location based on proton energy and the characteristics of the phoswhich scintillator detector. While initially promising, the model showed of limited use. The biggest limiting factor was the inconsistencies that originate in the detector themselves. It is not possible to account for the unique characteristics of each single detector, using the methods developed here. This could be changed if the individual characteristics of the detectors are taken into account in a future analysis.

<p>The study of high power fusion plasmas at the JET tokamak has been further enhanced through the development of instrumentation for neutron emission spectroscopy (NES) measurements. This has involved the upgrade of the magnetic proton recoil (MPR) spectrometer used for deuterium-tritium plasmas earlier so that the MPRu can now be also employed for deuterium (D) plasmas. A neutron time-of-flight (TOF) spectrometer designed for optimized rate (TOFOR) has been constructed and put into operation. The MPRu and TOFOR spectrometers were carried out as part of the JET enhanced performance program and represent the most advanced instrumentation for NES diagnosis of both D and DT tokamak plasmas setting a central platform for R&D direct to the next step in fusion research to be carried out with ITER.</p><p>The MPRu work presented in this thesis concerns the development of a new focal plane detector based on the phoswich scintillator technique. The main objective of this sub-project was to increase the signal-to-background ratio to permit measurement of the 2.5-MeV neutron emission from d+d-->3He+n reactions and, hence, allow NES diagnosis of D plasmas. The objective was achieved as demonstrated in preliminary measurements at JET. </p><p>The development of TOFOR from concept to construction is presented in the thesis including, in particular, the commissioning of the instrument at JET. The objective of the TOFOR project was to achieve the same high performance in the NES diagnosis of D plasmas as had earlier been demonstrated by the MPR for DT plasmas. TOFOR has been used in the first plasma physics experiments reported in this thesis. These demonstrate that the performance objectives have been achieved as tested, in particular, in the observation of auxiliary heating effects on velocity distribution of the deuterium population.</p>

It is possible to obtain information about various properties of the fuel ions deuterium (D) and tritium (T) in a fusion plasma by measuring the neutron emission from the plasma. Neutrons are produced in fusion reactions between the fuel ions, which means that the intensity and energy spectrum of the emitted neutrons are related to the densities and velocity distributions of these ions. This thesis describes different methods for analyzing data from fusion neutron measurements. The main focus is on neutron spectrometry measurements, using data used collected at the tokamak fusion reactor JET in England. Several neutron spectrometers are installed at JET, including the time-of-flight spectrometer TOFOR and the magnetic proton recoil (MPRu) spectrometer. Part of the work is concerned with the calculation of neutron spectra from given fuel ion distributions. Most fusion reactions of interest – such as the D + T and D + D reactions – have two particles in the final state, but there are also examples where three particles are produced, e.g. in the T + T reaction. Both two- and three-body reactions are considered in this thesis. A method for including the finite Larmor radii of the fuel ions in the spectrum calculation is also developed. This effect was seen to significantly affect the shape of the measured TOFOR spectrum for a plasma scenario utilizing ion cyclotron resonance heating (ICRH) in combination with neutral beam injection (NBI). Using the capability to calculate neutron spectra, it is possible to set up different parametric models of the neutron emission for various plasma scenarios. In this thesis, such models are used to estimate the fuel ion density in NBI heated plasmas and the fast D distribution in plasmas with ICRH.

The study of high power fusion plasmas at the JET tokamak has been further enhanced through the development of instrumentation for neutron emission spectroscopy (NES) measurements. This has involved the upgrade of the magnetic proton recoil (MPR) spectrometer used for deuterium-tritium plasmas earlier so that the MPRu can now be also employed for deuterium (D) plasmas. A neutron time-of-flight (TOF) spectrometer designed for optimized rate (TOFOR) has been constructed and put into operation. The MPRu and TOFOR spectrometers were carried out as part of the JET enhanced performance program and represent the most advanced instrumentation for NES diagnosis of both D and DT tokamak plasmas setting a central platform for R&amp;D direct to the next step in fusion research to be carried out with ITER. The MPRu work presented in this thesis concerns the development of a new focal plane detector based on the phoswich scintillator technique. The main objective of this sub-project was to increase the signal-to-background ratio to permit measurement of the 2.5-MeV neutron emission from d+d--&gt;3He+n reactions and, hence, allow NES diagnosis of D plasmas. The objective was achieved as demonstrated in preliminary measurements at JET. The development of TOFOR from concept to construction is presented in the thesis including, in particular, the commissioning of the instrument at JET. The objective of the TOFOR project was to achieve the same high performance in the NES diagnosis of D plasmas as had earlier been demonstrated by the MPR for DT plasmas. TOFOR has been used in the first plasma physics experiments reported in this thesis. These demonstrate that the performance objectives have been achieved as tested, in particular, in the observation of auxiliary heating effects on velocity distribution of the deuterium population.

<p>When the heavy hydrogen isotopes deuterium (D) and tritium (T) undergo nuclear fusion large amounts of energy are released. At the Joint European Torus (JET) research is performed on how to harvest this energy. Two of the most important fusion reactions, d+d→³He+n (E_n = 2.5 MeV) and d+t→⁴He+n (E_n = 14 MeV), produce neutrons. This thesis investigates how measurements of these neutrons can provide information on the fusion performance.</p><p>The Magnetic Proton Recoil (MPR) neutron spectrometer has operated at JET since 1996. The spectrometer was designed to provide measurements on the 14 MeV neutron emission in DT operation, thereby conveying information on the state of the fuel ions. However, a majority of today’s fusion experiments are performed with pure D fuel. Under such conditions, the measurements with the MPR were severely hampered due to interfering background. This prompted an upgrade of the instrument. The upgrade, described in this thesis, included a new focal plane detector, a phoswich scintillator array, and new data acquisition electronics, based on transient recorder cards. This combination allows for pulse shape discrimination techniques to be applied and a signal to background of 5/1 has been achieved in measurements of the 2.5-MeV neutrons in D experiments. The upgrade also includes a new control and monitoring system, which enables the monitoring and correction of gain variations in the spectrometer’s photo multiplier tubes. Such corrections are vital for obtaining good data quality.</p><p>In addition, this thesis describes a new method for determining the total neutron yield and hence the fusion power by using a MPR spectrometer in combination with a neutron emission profile monitor. The system has been operated at JET both during DT and D experiments. It is found that the systematic uncertainties are considerably lower (≈6 %) than for traditional systems. For a dedicated system designed for the next generation fusion experiments, i.e, ITER, uncertainties of 4 % could be attained.</p><p>Neutron spectroscopy can also be an important tool for determining the neutron emission from residual tritium in D plasmas. This information is combined with other measurements at JET in order to determine the confinement of the 1 MeV tritons from the d+d→t+p reactions.</p>

Neutron are emitted from a deuterium plasma with energies around 2.5 MeV. The neutron spectrum is intimately related to the ion velocity distribution of the plasma. As a consequence, the analysis of neutron energy spectra can give information of the plasma rotation, the ion temperature, heating efficiency and fusion power. The upgraded magnetic proton recoil spectrometer (MPRu), based on the thin-foil technique, is installed at the tokamak JET. The upgrade of the spectrometer was done to allow for measurements of deuterium plasmas. This thesis describes the hardware, the data reduction scheme and the kind of fusion plasma parameters that can be estimated from the data of the MPRu. The MPRu data from 3rd harmonic ion cyclotron resonance and beam heating are studied. Other neutron spectrometer techniques are reviewed as well, in particular in the aspect of suitability for neutron emission spectrometry at ITER. Each spectrometer technique is evaluated using synthetic data which is obtained from standard scenarios of ITER. From this evaluation, we conclude that the thin-foil technique is the best technique to measure, e.g., the ion temperature in terms of time resolution.

When the heavy hydrogen isotopes deuterium (D) and tritium (T) undergo nuclear fusion large amounts of energy are released. At the Joint European Torus (JET) research is performed on how to harvest this energy. Two of the most important fusion reactions, d+d→3He+n (En = 2.5 MeV) and d+t→4He+n (En = 14 MeV), produce neutrons. This thesis investigates how measurements of these neutrons can provide information on the fusion performance. The Magnetic Proton Recoil (MPR) neutron spectrometer has operated at JET since 1996. The spectrometer was designed to provide measurements on the 14 MeV neutron emission in DT operation, thereby conveying information on the state of the fuel ions. However, a majority of today’s fusion experiments are performed with pure D fuel. Under such conditions, the measurements with the MPR were severely hampered due to interfering background. This prompted an upgrade of the instrument. The upgrade, described in this thesis, included a new focal plane detector, a phoswich scintillator array, and new data acquisition electronics, based on transient recorder cards. This combination allows for pulse shape discrimination techniques to be applied and a signal to background of 5/1 has been achieved in measurements of the 2.5-MeV neutrons in D experiments. The upgrade also includes a new control and monitoring system, which enables the monitoring and correction of gain variations in the spectrometer’s photo multiplier tubes. Such corrections are vital for obtaining good data quality. In addition, this thesis describes a new method for determining the total neutron yield and hence the fusion power by using a MPR spectrometer in combination with a neutron emission profile monitor. The system has been operated at JET both during DT and D experiments. It is found that the systematic uncertainties are considerably lower (≈6 %) than for traditional systems. For a dedicated system designed for the next generation fusion experiments, i.e, ITER, uncertainties of 4 % could be attained. Neutron spectroscopy can also be an important tool for determining the neutron emission from residual tritium in D plasmas. This information is combined with other measurements at JET in order to determine the confinement of the 1 MeV tritons from the d+d→t+p reactions.

This thesis describes the development of electronic modules for fusion neutron spectroscopy as well as several implementations of artificial neural networks (NN) for neutron diagnostics for the Joint European Torus (JET) experimental reactor in England. The electronics projects include the development of two fast light pulser modules based on Light Emitting Diodes (LEDs) for the calibration and stability monitoring of two neutron spectrometers (MPRu and TOFOR) at JET. The particular electronic implementation of the pulsers allowed for operation of the LEDs in the nanosecond time scale, which is typically not well accessible with simpler circuits. Another electronic project consisted of the the development and implementation at JET of 32 high frequency analog signal amplifiers for MPRu. The circuit board layout adopted and the choice of components permitted to achieve bandwidth above 0.5 GHz and low distortion for a wide range of input signals. The successful and continued use of all electronic modules since 2005 until the present day is an indication of their good performance and reliability. The NN applications include pulse shape discrimination (PSD), deconvolution of experimental data and tomographic reconstruction of neutron emissivity profiles for JET. The first study showed that NN can perform neutron/gamma PSD in liquid scintillators significantly better than other conventional techniques, especially for low deposited energy in the detector. The second study demonstrated that NN can be used for statistically efficient deconvolution of neutron energy spectra, with and without parametric neutron spectroscopic models, especially in the region of low counts in the data. The work on tomography provided a simple but effective parametric model for describing neutron emissivity at JET. This was then successfully implemented with NN for fast and automatic tomographic reconstruction of the JET camera data. The fast execution time of NN, i.e. usually in the microsecond time scale, makes the NN applications presented here suitable for real-time data analysis and typically orders of magnitudes faster than other commonly used codes. The results and numerical methods described in this thesis can be applied to other diagnostic instruments and are of relevance for future fusion reactors such as ITER, currently under construction in Cadarache, France.