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Recent advancements in plasma physics are intensifying the demand for advanced diagnostic techniques in fusion research, particularly for the upcoming ITER fusion reactor. The ITER fusion reactor is projected to be ten times more powerful than its predecessors, imposing higher constraints on operational parameters. To meet ITER's requirements, such as the fuel ion ratio n_t/n_d and fuel ion temperature T_i, a High Resolution Neutron Spectrometer System (HRNS) has been proposed.

This thesis focuses on the Thin-foil proton recoil (TPR) spectrometer, an integral part of the HRNS, with an emphasis on its application and validation within the ITER context. The research encompasses two main areas: spectrometer simulations and experimental validation. Through a combination of custom transport code and Geant4 simulations, the study investigates the optimization of the TPR spectrometer's design in terms of efficiency and energy resolution. Additionally, selected design performance under ITER-like conditions has been investigated. These simulations are critical in assessing the spectrometer's capabilities and limitations during operation at ITER. Subsequent experimental validation, conducted using a DT neutron generator and a TPR spectrometer prototype, verified the existing simulation framework in terms of energy resolution and background discrimination methods.  

We examined a  Tandem neutron spectrometer, used in fusion plasma diagnostics at JET to further investigate TPR spectrometer diagnostic possibilities.  Tandem spectrometer was operational during JET's first DT campaign, the  spectrometer shares the neutron detection principles of the TPR. The fuel ion ratio n_t/n_tot  was determined using the Tandem data together with inputs from PENCIL or TRANSP,  for previously not analysed JET discharges. Our findings indicate that estimation of  n_t/n_tot is feasible using either PENCIL or TRANSP. Furthermore, the research demonstrates that TPR based neutron spectrometers can be effectively used in fuel ion ratio determination. 

In conclusion, this research significantly advances fusion plasma diagnostics. It validates the TPR spectrometer's design in terms of energy resolution and efficiency for ITER, predicting a signal-to-background ratio of approximately 550 and a maximum count rate of 120kHz. The results from the TPR prototype experiment, replicated with the Geant4 simulation, along with comparative analysis with the JET's Tandem spectrometer, highlight the TPR spectrometer's broad applicability in fusion diagnostics, marking a major advancement in the field.