Measurements of neutron emission from a fusion plasma can provide a wealth of information on the underlying temporal, spatial and energy distributions of reacting ions and how they are affected by a wide range of magneto-hydro-dynamic (MHD) instabilities. This thesis focuses on the interpretation of the experimental measurements recorded by neutron flux monitors with and without spectroscopic capabilities installed on the Mega Ampere Spherical Tokamak (MAST). In particular, the temporally and spatially resolved measurements of the neutron rate measured by the neutron camera, which also possesses spectroscopic capabilities, are combined with the temporally resolved measurements of the total neutron rate provided by the absolutely calibrated fission chamber in order to study the properties of the fast ion distributions in different plasma scenarios. The first part of the thesis describes in detail the two forward modelling methods, which employ the set of interconnected codes developed to interpret experimental observations such as neutron count rate profiles and recoil proton pulse height spectra provided by the neutron camera. In the second part of the thesis the developed methods are applied to model the neutron camera observations performed in a variety of plasma scenarios. The first method, which involves only TRANSP/NUBEAM and LINE2 codes, was used to validate the neutron count rate profiles measured by the neutron camera in three different plasma scenarios covering the wide range of total neutron rate typically observed on MAST. In addition, the first framework was applied to model the changes in the total and local neutron rates caused by fishbone instability as well as to estimate the Hydrogen and Deuterium ion ratio. The second modelling method, which involves TRANSP/NUBEAM, LINE2, DRESS and NRESP, was used to validate the measured recoil proton pulse height spectra in a MHD-quiescent plasma scenario.

Measurements of the neutron emission, resulting from nuclear fusion reactions between the hydrogen isotopes deuterium and tritium, can provide a wealth of information on the confinement properties of fusion plasmas and how these are affected by Magneto-Hydro-Dynamic (MHD) instabilities. This thesis describes work aimed to develop neutron measurement techniques for nuclear fusion plasma experiments, specifically regarding the performance and design of collimated neutron flux monitors (neutron cameras) for the Mega Ampere Spherical Tokamak, MAST, and for MAST Upgrade. The first part of the thesis focuses on the characterization of a prototype neutron camera installed at MAST and provides an account of the very first measurements of the neutron emissivity along its collimated fields of view. It is shown that the camera has sufficient temporal and spatial resolution to measure the effect of MHD instabilities on the neutron emissivity. The neutron camera fulfils the requirement on the measurements of the neutron count rate profile with less than 10 % statistical uncertainty in a time resolution of 1 ms. The instrument's more rudimentary capabilities to provide information on the neutron energy distribution are also presented and discussed. The encouraging results obtained with the prototype neutron camera show the potential of a collimated neutron flux monitor at MAST and suggest that an upgraded instrument for MAST Upgrade will provide crucial information on fast ions behavior and other relevant physics issues. The design of such an upgraded instrument for MAST Upgrade is discussed in the second part of the thesis. Two design options are explored, one consisting of two collimator arrays in the horizontal direction, another more traditional design with lines-of-sight in the poloidal cross section plane. On the basis of the experience gained with the prototype neutron camera and on the exploratory design and estimated performance for the upgraded camera presented here, a conceptual design of a neutron camera upgrade is proposed.

The γ-ray characterizing possibility of the neutron collimated flux monitor (in short, Neutron Camera) at the Mega Ampere Spherical Tokamak (MAST) is explored. Typically used to monitor neutron emission, the Neutron Camera has excellent neutron/γ-ray discrimination properties and thus presents the opportunity to measure spatially and temporally resolved γ-ray emission - a possibility of an additional fusion diagnostics method with already existing equipment. An Online Data Analysis (ODA) code was used to analyze the data on γ-rays from several plasma discharges with similar plasma parameters. A high statistics temporal distribution of the γ-ray emission and a lower statistics spatial distribution were analyzed. However, the low energy resolution and range for the Neutron Camera γ-ray measurements revealed few conclusive results on the origin of the higher energy γ-rays. Detection systems with higher energy resolution and range are suggested for an extensive analysis of γ-ray emission at MAST Upgrade.

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.