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A python code was developed to compute the alpha knock-on (AKN) neutron spectrum using two already available computational tools. The code was used to calculate the AKN for a given discharge from the DTE2 JET campaign. Results showed that the beam-target contribution dominated the neutron spectra and obscured the AKN tail. A spatial profile of the AKN intensity was created which showed that the majority of the AKN reactions happen in the center of the plasma, but further analysis is needed to get a better picture of whether the AKN component will be measurable or not.

Fast magnetosonic waves in the ion cyclotron range of frequencies have the potential to heat plasma and drive current in a thermonuclear fusion reactor. A code, SELFO-light, has been developed to study the physics of ion cyclotron resonantheating and current drive in thermonuclear fusion reactors. It uses a global full wave solver LION and a new 1D Fokker-Planck solver for the self-consistent calculations of the wave field and the distribution function of ions.In present day tokamak experiments like DIII-D and JET, fast wave damping by ions at higher harmonic cyclotron frequencies is weak compared to future thermonuclear tokamak reactors like DEMO. The strong damping by deuterium, tritium and thermonuclear alpha-particles and the large Doppler width of fast alpha-particles in DEMO makes it difficult to drive the current when harmonic resonance layers of these ionspecies are located at low field side of the magnetic axis. At higher harmonic frequencies the possibility of fast wave current drive diminishes due to the overlapping of alpha-particle harmonic resonance layers. Narrow frequency bands suitable for the fast wave current drive in DEMO have been identified at lower harmonics of the alpha-particles. For these frequencies the effect of formation of high-energy tails in the distribution function of majority and minority ion species on the current drive have been studied. Some of these frequencies are found to provide efficient ion heating in the start up phase of DEMO. The spectrum where efficient current drive can be obtained is restricted due to weak electron damping at lower toroidal mode numbers and strong trapped electron damping at higher toroidal mode numbers. The width of toroidal mode spectra for which efficient current drive can be obtained have been identified, which has important implications for the antenna design. / <p>QC 20130327</p>

Cette thèse porte sur l'interaction entre un plasma de bord de tokamak et une perturbation magnétique résonante (RMP), utilisée principalement pour le contrôle de phénomènes de relaxations quasi-périodiques, présents dans un régime de confinement amélioré. Il permet notamment d'atteindre des conditions favorables aux réactions de fusion nucléaire. Il a été observé que la présence de perturbations magnétiques modifie la topologie magnétique au bord ce qui engendre une diminution de l'amplitude des relaxations, voire leur suppression. De précédents travaux ont étudié l'effet de perturbations magnétiques sur un plasma relaxant via des simulations numériques. Le modèle utilisé était dans un cas électrostatique, c'est à dire que la topologie magnétique n'évoluait pas dans le temps. Dans cette thèse, l'étude est faite dans un modèle de plasma de bord prenant en compte les fluctuations magnétiques via le code numérique EMEDGE3D. Ce code a été modifié pour pouvoir imposer une perturbation magnétique résonante. Des vérifications par des modèles réduits ont été menées sur la pénétration d'une perturbation magnétique ainsi que sur l'effet d'une vitesse cisaillée sur la pénétration. Ensuite, un RMP a été imposé dans un plasma non turbulent avec et sans vitesse cisaillée. Un phénomène d'écrantage, empêchant la pénétration d'une perturbation, a été identifié analytiquement et observé dans les simulations. Cette étude a été réitérée dans un plasma turbulent, et aussi en présence d'une barrière (vitesse cisaillée). Le plasma turbulent engendre une amplification du RMP, tandis que la barrière est affectée par la présence de cellules de convection fixes générées par la perturbation. / In this thesis, the interaction between tokamak edge plasma and resonant magnetic perturbation (RMPs) is studied. It is mainly used to mitigate quasi-periodic relaxations in enhanced confinement regime. This regime allows to obtain good conditions for nuclear fusion. Introduction of a RMP in a tokamak plasma has been observed to modified the magnetic topology at the edge and decrease the relaxation amplitude up to complete suppression. Previous works studied the RMP effect on a plasma with relaxations, via numerical simulations. The model used for that consider the electrostatic approximation, where the magnetic topology does not evolve in time. In this thesis, the study is done with an edge plasma model taking into account magnetic fluctuations via the numerical code EMEDGE3D. This code has been modified to include the resonant magnetic perturbation. Comparison with reduced models has been carried out on the RMP penetration and the effect of sheared velocity on it. Then a RMP has been induced in a stable plasma, with or without imposed sheared rotation. A condition on the sheared velocity has been identified to avoid the screening effect, that would prevent the RMP penetration, analytically and in numerical simulations. This works has been repeated in a turbulent plasma in presence or not of transport barrier (sheared velocity). The turbulent plasma generate an effective RMP amplification, while the transport barrier is affected by locked convective cells due to the RMP.

Title: Materials for fusion applications and their interaction with tokamak plasma Author: Veronika Klevarová Department: Department of Physics of Materials Supervisor: doc. RNDr. Miloš Janeček, CSc., Department of Physics of Materials Abstract: Tungsten represents a perspective option in the context of fusion devices first-wall materials. In the first part of this work, set of tungsten samples with variable grain size was prepared by spark plasma sintering. Specimens were exposed to steady state deuterium plasma beam and high energy heat pulses, simulating thus the normal operation in the tokamak. As a consequence of the exposure, samples surfaces were roughened, as-prepared grains were recovered and in some cases cracks were formed. Moreover, post-irradiation analysis of the damaged samples revealed activation of in-grain slip systems within the loaded surfaces. Threshold grain diameter for this mechanism was determined to be between 5.5 - 6.6 μm at the particular loading conditions. However, damaged features showed to depend more on the fabrication parameters than on the grain diameter. Synergistic effects of simultaneous loading were proven to be important since those reduced the heat propagation within the volume of the tested samples. In the second part of this thesis, introduction to plasma-surface...

Neste trabalho são abordados alguns aspectos do tokamak TCABR, particularmente no que diz respeito à ruptura do plasma, às descargas e ao sistema vertical. Desenvolveu-se um modelo zero-dimensional para modelagem das descargas, envolvendo 5 equações diferenciais. Com esse modelo obteve-se os perfis temporais de parâmetros importantes da descarga tais como: corrente de plasma, tensão de enlace, temperatura eletrônica, densidade eletrônica e densidade de partículas neutras. Verificou-se, com as simulações, a influência de parâmetros importantes no comportamento das descargas. A partir de resultados experimentais do TCA e do TCABR verificou-se a compatibilidade desses resultados com o modelo. Fez-se um estudo da ruptura do plasma no TCABR utilizando-se um modelo físico para os processos que envolvem a ruptura com o qual pode-se delimitar a região de ruptura que depois pode ser comparada com os resultados experimentais. Experimentalmente verificou-se que, para o TCABR, a ruptura ocorre para pressões entre 9.10-6 a 3.10-4 mbar e campos elétricos entre 2 e 10 V/m. A relação campo-pressão, E/p, na região de ruptura, está entre 3.107 e 5.108 V.m-1.bar-1. Foi também feito um estudo do sistema de controle realimentado do campo vertical onde determinou-se algumas funções de transferências importantes, particularmente para os blocos não lineares desse sistema. A partir de um programa computacional foi feito um mapeamento do campo vertical e do índice de curvatura do campo. Verificou-se que a razão entre a componente vertical do campo, no centro do vaso, e o valor correspondente de corrente que passa pelas espiras é de 3,5.10-5 T/A e o índice de curvatura do campo está em torno de 0,45. / In this work, some aspects of the TCABR tokamak are studied. In particular, some points concerned to the plasma breakdown, to discharge characteristics in tokamak mode and to the vertical field system are investigated. A zero-dimensional model has been developed, especially for this work, based on five differential equations involving the ohmic heating circuit and the conservation laws of energy, electrical charge and neutral particles. The model was used for simulating the TCABR plasma discharges. Therefore, time profiles of important plasma parameters like plasma current, loop voltage, electron temperature, electron density and neutral density, were obtained. Also, as a result of the simulations, was verified how the tokamak machine parameters and plasma parameters influence the behavior of the discharges. Some experimental results from the TCABR and TCA were compared with the results of the simulations. A study of the rupture of the plasma was carried out adopting a physical model that includes many physical processes. This model was used to delimit the breakdown region for TCABR tokamak machine and as a tool to understand the experimental data. Experimentally, it was observed that, for TCABR, the rupture occurs for pressures values between 1.10-5 to 3.10-4 mbar, and electric fields values between 2 and 10 V/m. The ratio electric field-pressure (E/p), in the rupture region, is between 3.107 and 5.108 V.m-1.bar-1. For the control system of the vertical field we obtained some transfer functions mainly for the non-linear blocks of the system that have been used in the experimental tests. A computer program was developed to obtain the map of the magnetic vertical field lines and the index of curvature of the field. Finally it was verified that, in the center of the vessel, the ratio between the magnetic vertical field to the electric current that flows in the vertical coils is, 3.5.10-5 T/A and the index of curvature of the field is ~0.45.

This thesis concerns modelling of Coulomb collisions in toroidal plasma with Monte Carlo operators, which is important for many applications such as heating, current drive and collisional transport in fusion plasmas. Collisions relax the distribution functions towards local isotropic ones and transfer power to the background species when they are perturbed e.g. by wave-particle interactions or injected beams. The evolution of the distribution function in phase space, due to the Coulomb scattering on background ions and electrons and the interaction with RF waves, can be obtained by solving a Fokker-Planck equation.The coupling between spatial and velocity coordinates in toroidal plasmas correlates the spatial diffusion with the pitch angle scattering by Coulomb collisions. In many applications the diffusion coefficients go to zero at the boundaries or in a part of the domain, which makes the SDE singular. To solve such SDEs or equivalent diffusion equations with Monte Carlo methods, we have proposed a new method, the hybrid method, as well as an adaptive method, which selects locally the faster method from the drift and diffusion coefficients. The proposed methods significantly reduce the computational efforts and improves the convergence. The radial diffusion changes rapidly when crossing the trapped-passing boundary creating a boundary layer. To solve this problem two methods are proposed. The first one is to use a non-standard drift term in the Monte Carlo equation. The second is to symmetrize the flux across the trapped passing boundary. Because of the coupling between the spatial and velocity coordinates drift terms associated with radial gradients in density, temperature and fraction of the trapped particles appear. In addition an extra drift term has been included to relax the density profile to a prescribed one. A simplified RF-operator in combination with the collision operator has been used to study the relaxation of a heated distribution function. Due to RF-heating the density of thermal ions is reduced by the formation of a high-energy tail in the distribution function. The Coulomb collisions tries to restore the density profile and thus generates an inward diffusion of thermal ions that results in a peaking of the total density profile of resonant ions. / <p>QC 20130415</p>

Neste trabalho são abordados alguns aspectos do tokamak TCABR, particularmente no que diz respeito à ruptura do plasma, às descargas e ao sistema vertical. Desenvolveu-se um modelo zero-dimensional para modelagem das descargas, envolvendo 5 equações diferenciais. Com esse modelo obteve-se os perfis temporais de parâmetros importantes da descarga tais como: corrente de plasma, tensão de enlace, temperatura eletrônica, densidade eletrônica e densidade de partículas neutras. Verificou-se, com as simulações, a influência de parâmetros importantes no comportamento das descargas. A partir de resultados experimentais do TCA e do TCABR verificou-se a compatibilidade desses resultados com o modelo. Fez-se um estudo da ruptura do plasma no TCABR utilizando-se um modelo físico para os processos que envolvem a ruptura com o qual pode-se delimitar a região de ruptura que depois pode ser comparada com os resultados experimentais. Experimentalmente verificou-se que, para o TCABR, a ruptura ocorre para pressões entre 9.10-6 a 3.10-4 mbar e campos elétricos entre 2 e 10 V/m. A relação campo-pressão, E/p, na região de ruptura, está entre 3.107 e 5.108 V.m-1.bar-1. Foi também feito um estudo do sistema de controle realimentado do campo vertical onde determinou-se algumas funções de transferências importantes, particularmente para os blocos não lineares desse sistema. A partir de um programa computacional foi feito um mapeamento do campo vertical e do índice de curvatura do campo. Verificou-se que a razão entre a componente vertical do campo, no centro do vaso, e o valor correspondente de corrente que passa pelas espiras é de 3,5.10-5 T/A e o índice de curvatura do campo está em torno de 0,45. / In this work, some aspects of the TCABR tokamak are studied. In particular, some points concerned to the plasma breakdown, to discharge characteristics in tokamak mode and to the vertical field system are investigated. A zero-dimensional model has been developed, especially for this work, based on five differential equations involving the ohmic heating circuit and the conservation laws of energy, electrical charge and neutral particles. The model was used for simulating the TCABR plasma discharges. Therefore, time profiles of important plasma parameters like plasma current, loop voltage, electron temperature, electron density and neutral density, were obtained. Also, as a result of the simulations, was verified how the tokamak machine parameters and plasma parameters influence the behavior of the discharges. Some experimental results from the TCABR and TCA were compared with the results of the simulations. A study of the rupture of the plasma was carried out adopting a physical model that includes many physical processes. This model was used to delimit the breakdown region for TCABR tokamak machine and as a tool to understand the experimental data. Experimentally, it was observed that, for TCABR, the rupture occurs for pressures values between 1.10-5 to 3.10-4 mbar, and electric fields values between 2 and 10 V/m. The ratio electric field-pressure (E/p), in the rupture region, is between 3.107 and 5.108 V.m-1.bar-1. For the control system of the vertical field we obtained some transfer functions mainly for the non-linear blocks of the system that have been used in the experimental tests. A computer program was developed to obtain the map of the magnetic vertical field lines and the index of curvature of the field. Finally it was verified that, in the center of the vessel, the ratio between the magnetic vertical field to the electric current that flows in the vertical coils is, 3.5.10-5 T/A and the index of curvature of the field is ~0.45.

This thesis concerns heating and current drive in tokamak plasmas using the fast magnetosonic wave in the ion cyclotron range of frequencies. Fast wave heating is a versatile heating method for thermonuclear fusion plasmas and can provide both ion and electron heating and non-inductive current drive. Predicting and interpreting realistic heating scenarios is however difficult due to the coupled evolution of the cyclotron resonant ion velocity distributions and the wave field. The SELFO code, which solves the coupled wave equation and Fokker-Planck equation for cyclotron resonant ion species in a self-consistent manner, has been upgraded to allow the study of more advanced fast wave heating and current drive scenarios in present day experiments and in preparation for the ITER tokamak. Theoretical and experimental studies related to fast wave heating and current drive with emphasis on fast ion effects are presented. Analysis of minority ion cyclotron current drive in ITER indicates that the use of a hydrogen minority rather than the proposed helium-3 minority results in substantially more efficient current drive. The parasitic losses of power to fusion born alpha particles and beam injected ions are concluded to be acceptably low. Experiments performed at the JET tokamak on polychromatic ion cyclotron resonance heating and on fast wave electron current drive are presented and analysed. Polychromatic heating is demonstrated to increase the bulk plasma ion to electron heating ratio, in line with theoretical expectations, but the fast wave electron current drive is found to be severely degraded by parasitic power losses outside of the plasma. A theoretical analysis of parasitic power losses at radio frequency antennas indicates that the losses can be significantly increased in scenarios with low wave damping and with narrow antenna spectra, such as in electron current drive scenarios. / QC 20100506