A novel photon flux monitor has been designed and tested for use at the Duke University High Intensity Gamma Source, where the photon beam produced is essentially mono-energetic but it is not tagged. Direct counting of the number of photons using a high-efficiency detector is not possible because of the high photon fluxes expected. Therefore, a direct counting detector with a low, accurately known efficiency was required.<p> The photon flux monitor based on a five scintillator paddle system detects recoil electrons and positrons from photoelectric, Compton and pair-production processes. It has been designed to be insensitive to gain and detector threshold changes and to be usable for photon energies above 5 MeV. It has been calibrated using direct counting with a NaI detector and its efficiency has been shown to be well predicted by a GEANT4 simulation.<p> Results of measurements, calibration and calculations required to characterize the 5-paddle photon flux monitor are presented. The photon flux monitor has met its design specifications of being able to determine the number of photons incident on it during the live time of a measurement to within a systematic error of 2%.<p> A paper based on the work for this thesis has been published in the Nuclear Instruments and Methods in Physics Research Journal.

A novel photon flux monitor has been designed and tested for use at the Duke University High Intensity Gamma Source, where the photon beam produced is essentially mono-energetic but it is not tagged. Direct counting of the number of photons using a high-efficiency detector is not possible because of the high photon fluxes expected. Therefore, a direct counting detector with a low, accurately known efficiency was required.<p> The photon flux monitor based on a five scintillator paddle system detects recoil electrons and positrons from photoelectric, Compton and pair-production processes. It has been designed to be insensitive to gain and detector threshold changes and to be usable for photon energies above 5 MeV. It has been calibrated using direct counting with a NaI detector and its efficiency has been shown to be well predicted by a GEANT4 simulation.<p> Results of measurements, calibration and calculations required to characterize the 5-paddle photon flux monitor are presented. The photon flux monitor has met its design specifications of being able to determine the number of photons incident on it during the live time of a measurement to within a systematic error of 2%.<p> A paper based on the work for this thesis has been published in the Nuclear Instruments and Methods in Physics Research Journal.

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.