<p>A MATLAB code for calculating neutron energy spectra from JET discharges was developed. The code uses the fuel ion distribution calculated by the computer code SELFO to generate the spectrum through a Monte-Carlo simulation. The calculated spectra were then compared against experimental results from the neutron spectrometer TOFOR. In the calculations, the exact orbits of the fuel ions are taken into account, in order to investigate what effects this has on the spectrum. The reason for this is that, for certain plasma heating scenarios, large populations of fast fuel ions are formed. These fast ions may have Larmor radii of the order of decimeters, which is comparable to the width of the sight line of TOFOR, and may therefore affect the recorded neutron spectrum. A JET discharge with both NBI and 3rd harmonic ICRF heating was analyzed. The results show that the details of the line of sight of the detector indeed affects the neutron spectrum. This effect is probably important for other diagnostics techniques, such as gamma-ray spectroscopy and neutral particle analysis, as well. Good agreement with TOFOR data is observed, but not for the exact same time slice of the discharge, which leaves some questions yet to be investigated.</p>

A MATLAB code for calculating neutron energy spectra from JET discharges was developed. The code uses the fuel ion distribution calculated by the computer code SELFO to generate the spectrum through a Monte-Carlo simulation. The calculated spectra were then compared against experimental results from the neutron spectrometer TOFOR. In the calculations, the exact orbits of the fuel ions are taken into account, in order to investigate what effects this has on the spectrum. The reason for this is that, for certain plasma heating scenarios, large populations of fast fuel ions are formed. These fast ions may have Larmor radii of the order of decimeters, which is comparable to the width of the sight line of TOFOR, and may therefore affect the recorded neutron spectrum. A JET discharge with both NBI and 3rd harmonic ICRF heating was analyzed. The results show that the details of the line of sight of the detector indeed affects the neutron spectrum. This effect is probably important for other diagnostics techniques, such as gamma-ray spectroscopy and neutral particle analysis, as well. Good agreement with TOFOR data is observed, but not for the exact same time slice of the discharge, which leaves some questions yet to be investigated.

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.

As tentativas de se conseguir um funcionamento contínuo para o tokamak e as perspectivas de estabilização de oscilações MHD através do controle do perfil de corrente, motivaram pesquisas que levassem a uma forma de geração de corrente não indutiva. Uma das possíveis alternativas para atingir esta meta é a injeção de ondas de alta freqüência como, por exemplo, ondas na freqüência híbrida inferior ou Lower Hybrid (LH), que impulsionam elétrons através do amortecimento de Landau na direção paralela ao campo magnético toroidal, tomando-os capazes de transportar corrente. Nos futuros reatores, entretanto, a absorção da onda pelas partículas de 3.5 MeV, conforme o que é previsto, e que ocorre através do amortecimento de Landau na direção perpendicular ao campo magnético, pode diminuir a eficiência do método descrito acima. Nosso objetivo, neste trabalho, é simular a interação LH-partículas com a interação entre a onda LHe os íons rápidos do plasma, que atingem até alguns MeV de energia e que são provenientes do aquecimento de íons de minoria pela onda ciclotrônica de íons (IC). Estes fenômenos podem ser descritos através de uma equação de Fokker-Planck uni-dimensional, no espaço de velocidades, onde os termos de difusão quase-linear, correspondentes à injeção das ondas IC e LH, estão presentes juntamente com os termos colisionais, que representam a termalização dos íons rápidos sobre um plasma maxwelliano. Apresentamos, aqui, as primeiras evidências experimentais da interação LH-íons rápidos no tokamak JET. A análise de dados foi baseada na observação do conteúdo energético dos íons de minoria e das taxas de emissão de raios e de nêutrons no plasma, toda vez que a onda LH estava presente simultaneamente ao aquecimento com ondas IC. Observamos, nesta situação, que há um aumento de cerca de 20% do conteúdo energético dos íons rápidos, que corresponde a uma potência da onda absorvida de até, aproximadamente, 25%, dependendo dos parâmetros do plasma. O aumento de emissão de raios e de nêutrons, provenientes das reações de fusão, também confrrmou o aumento de energia dos íons rápidos quando a onda LH estava presente. Análises com FFT em experimentos onde a potência da onda estava 100% modulada, propiciaram o estudo da absorção de potência da onda LH de acordo com os níveis de superposição dos dois perfis de deposição sobre o plasma (ICe LH). / Attempts to achieve a steady-state operation in a reactor regime and the possibilities of stabilising MHD oscillations by controlling the plasma current density profile motivated studies of different methods of generating non-inductive current in reactor scenarios. The injection of Lower Hybrid waves (LH) in tokamak plasmas is considered as a possible route to reach this goal and has been successfully employed to generate plasma current by transferring momentum to the electrons in the direction parallel to the magnetic field through Electron Landau Damping (ELD). However, in a reactor operation regime, LHCD (Lower Hybrid Current Drive) efficiency can be affected, as it is predicted, by the damping of the wave on the 3.5 MeV particles, produced during fusion reactions. This interaction occurs through perpendicular Landau Damping since the particles can be considered as unmagnetized. In this work, the interaction of LH waves with particles is simulated through the interaction between the LH wave and ICRH driven minority íons, that can reach energies up to few MeV. Both phenomena can be described by a 1-D Fokker-Planck equation in velocity space that includes both quasi-linear diffusion coefficients due to ICRH and LH waves and collision terms which represent the fast ions slowing-down over a maxwellian plasma Once this Fokker-Planck equation is solved, the fast ion distribution function can be obtained in order to provide information on the fast minority íons. The first experimental evidence of the interaction of LH waves with ICRH minority íons in the MeV energy range is presented in this work. This interaction was detected in JET through measurements of the fast ion energy, ray and neutron ernission rates and by means of Fast Fourier Transform (FFT) analysis in experiments with 100% LH power modulation. An increase has been observed of approximately 20% in the fast ion energy content which corresponds about to 25% of LH power absorbed by the fast minority ions, depending on the plasma parameters. The increase of ray and neutron rates ernitted in the plasma and the FFT analysis confirm, respectively, the fast ion energy increase and a better damping of the wave when the overlap between IC and LH deposition profiles is maxirnized.

As tentativas de se conseguir um funcionamento contínuo para o tokamak e as perspectivas de estabilização de oscilações MHD através do controle do perfil de corrente, motivaram pesquisas que levassem a uma forma de geração de corrente não indutiva. Uma das possíveis alternativas para atingir esta meta é a injeção de ondas de alta freqüência como, por exemplo, ondas na freqüência híbrida inferior ou Lower Hybrid (LH), que impulsionam elétrons através do amortecimento de Landau na direção paralela ao campo magnético toroidal, tomando-os capazes de transportar corrente. Nos futuros reatores, entretanto, a absorção da onda pelas partículas de 3.5 MeV, conforme o que é previsto, e que ocorre através do amortecimento de Landau na direção perpendicular ao campo magnético, pode diminuir a eficiência do método descrito acima. Nosso objetivo, neste trabalho, é simular a interação LH-partículas com a interação entre a onda LHe os íons rápidos do plasma, que atingem até alguns MeV de energia e que são provenientes do aquecimento de íons de minoria pela onda ciclotrônica de íons (IC). Estes fenômenos podem ser descritos através de uma equação de Fokker-Planck uni-dimensional, no espaço de velocidades, onde os termos de difusão quase-linear, correspondentes à injeção das ondas IC e LH, estão presentes juntamente com os termos colisionais, que representam a termalização dos íons rápidos sobre um plasma maxwelliano. Apresentamos, aqui, as primeiras evidências experimentais da interação LH-íons rápidos no tokamak JET. A análise de dados foi baseada na observação do conteúdo energético dos íons de minoria e das taxas de emissão de raios e de nêutrons no plasma, toda vez que a onda LH estava presente simultaneamente ao aquecimento com ondas IC. Observamos, nesta situação, que há um aumento de cerca de 20% do conteúdo energético dos íons rápidos, que corresponde a uma potência da onda absorvida de até, aproximadamente, 25%, dependendo dos parâmetros do plasma. O aumento de emissão de raios e de nêutrons, provenientes das reações de fusão, também confrrmou o aumento de energia dos íons rápidos quando a onda LH estava presente. Análises com FFT em experimentos onde a potência da onda estava 100% modulada, propiciaram o estudo da absorção de potência da onda LH de acordo com os níveis de superposição dos dois perfis de deposição sobre o plasma (ICe LH). / Attempts to achieve a steady-state operation in a reactor regime and the possibilities of stabilising MHD oscillations by controlling the plasma current density profile motivated studies of different methods of generating non-inductive current in reactor scenarios. The injection of Lower Hybrid waves (LH) in tokamak plasmas is considered as a possible route to reach this goal and has been successfully employed to generate plasma current by transferring momentum to the electrons in the direction parallel to the magnetic field through Electron Landau Damping (ELD). However, in a reactor operation regime, LHCD (Lower Hybrid Current Drive) efficiency can be affected, as it is predicted, by the damping of the wave on the 3.5 MeV particles, produced during fusion reactions. This interaction occurs through perpendicular Landau Damping since the particles can be considered as unmagnetized. In this work, the interaction of LH waves with particles is simulated through the interaction between the LH wave and ICRH driven minority íons, that can reach energies up to few MeV. Both phenomena can be described by a 1-D Fokker-Planck equation in velocity space that includes both quasi-linear diffusion coefficients due to ICRH and LH waves and collision terms which represent the fast ions slowing-down over a maxwellian plasma Once this Fokker-Planck equation is solved, the fast ion distribution function can be obtained in order to provide information on the fast minority íons. The first experimental evidence of the interaction of LH waves with ICRH minority íons in the MeV energy range is presented in this work. This interaction was detected in JET through measurements of the fast ion energy, ray and neutron ernission rates and by means of Fast Fourier Transform (FFT) analysis in experiments with 100% LH power modulation. An increase has been observed of approximately 20% in the fast ion energy content which corresponds about to 25% of LH power absorbed by the fast minority ions, depending on the plasma parameters. The increase of ray and neutron rates ernitted in the plasma and the FFT analysis confirm, respectively, the fast ion energy increase and a better damping of the wave when the overlap between IC and LH deposition profiles is maxirnized.