The steady flow model is applied to ablatively accelerated spherical targets for inertial confinement fusion. A parameter study is conducted which identifies regions of good hydrodynamic efficiency. In the limit of very large acceleration the model is seen to become planar and can be used to treat some large aspect ratio shells. A model of charged particle beam driven ablation is presented. The ablation resulting from this form of energy deposition can resemble laser driven albation in some cases, but qualitatively different behavior occurs in certain regimes of the beam power and range. Laser energy deposition by inverse bremsstrahlung is also included. A procedure for descaling the dimensionless results of the steady flow model is presented. This allows for comparison of the model with experiments and numerical simulations.

Plusieurs évènements astrophysiques comme les novae, les supernovae de type Ia (SNeIa) et les sursauts X sont le résultat d'une combustion thermonucléaire explosive dans un plasma stellaire. Les supernovae comptent parmi les objets astrophysiques les plus fascinants tant sur le plan théorique que sur celui des observations. Au moment de l'explosion, la luminosité d'une supernova peut égaler celle de l'intégralité des autres étoiles de la galaxie. On admet aujourd’hui que les SNeIa résultent de l'explosion thermonucléaire d'une étoile naine blanche, un objet dense et compact composé de carbone et d'oxygène. Divers chemins évolutifs peuvent conduire à l’explosion de la naine blanche si celle-ci est membre d’un système stellaire binaire. Néanmoins, la nature du système binaire, les mécanismes d'amorçage et de propagation de la combustion thermonucléaire ainsi que le rapport carbone/oxygène au sein de l'étoile compacte ne sont pas encore clairement identifiés à ce jour. En ce qui concerne l’écoulement réactif, on invoque ainsi une détonation (Modèle sub-Chandrasekhar), une déflagration ou la transition d'une déflagration vers une détonation (Modèle Chandrasekhar). La détonation semble donc jouer un rôle prépondérant dans l'explication des SNeIa. Les difficultés de modélisation des détonations proviennent essentiellement (i) de la libération d'énergie en plusieurs étapes, de l’apparition d’échelles de temps et de longueurs caractéristiques très différentes (ii) des inhomogénéités de densité, de température et de composition du milieu dans lequel se propage le front réactif et qui donnent naissance aux structures cellulaires et autres instabilités de propagation du front (extinctions et réamorçages locaux). En plus de celles citées ci-dessus, deux autres difficultés majeures inhérentes à l'étude de ce mode de propagation dans les plasmas stellaires sont rencontrées : la complexité de l’équation d’état astrophysique et la cinétique nucléaire pouvant impliquer plusieurs milliers de nucléides couplés par plusieurs milliers de réactions. Ainsi, les premiers travaux impliquant une combustion thermonucléaire explosive ont été réalisés sur bases d'hypothèses simplificatrices comme l'équilibre nucléaire statistique instantané des produits de réactions ou l'utilisation d'un réseau réduit à une dizaine d'espèces nucléaires. Dans tous ces travaux, la détonation est assimilée à une discontinuité totalement réactive (détonation de Chapman-Jouguet ou CJ). La résolution de l'onde de détonation nécessite l'étude détaillée du processus nucléaire se déroulant dans la zone de réaction. Malheureusement, les supports de calculs actuels ne permettent pas encore ce type de simulations pour les détonations astrophysiques. Le modèle ZND qui constitue une description unidimensionnelle stationnaire de l’écoulement (plan ou courbé) constitue une excellente approximation de la réalité. Notre travail réexamine les résultats des calculs des structures des ondes de détonations stellaires dans les conditions de température, de densité et de composition envisagées dans les travaux de ce type (détonation CJ et ZND) réalisés jusqu’à présent mais avec une équation d’état appropriée aux plasmas stellaires et une cinétique nucléaire nettement plus riche ; le plus grand réseau jamais utilisé pour ce genre d’études (333 noyaux couplés par 3262 réactions), prenant en compte les données les plus récentes de la physique nucléaire (vitesses de réaction et fonctions de partition)./Several astrophysics events like novae, supernovae and X burts, result from an explosive thermonuclear burning in stellar plasma. Type Ia Supernovae (SNeIa) count amoung the most fascinating stellar objects, they can be more brighter than an entire galaxy. Astrophysic works show that SNeIa may result from a thermonuclear explosion of a compact and dense star called carbon-oxygen white dwarf. The ignition stage and the propagation mode of the thermonuclear combustion wave are not identified yet. The Deflagration-to-Detonation Transition process (or "delayed detonation") sims to give the best overall agrements with the observations : detonations can play appart in SNeIa events. Simulating thermonuclear detonations count same difficults. The most important are the burning length scales that spent over more than ten oders of magnitud, the nuclear kinetics that involve thousands of nuclids linked by thousands of nuclear reactions and the stellar plasma equation of state (EOS). Hydrodynamical simulations of detonation use very simplified ingedients like reduced reactions network and asymptotic EOS of completely electron degenerate stellar plasma. Our work is the modelling of these detonations using more representative EOS of the stallar plasma that includs ions, electrons, radiation and electron-pistron pairs. We also use a more detailed kinetic network, comprising 331 nuclids linked by 3262 capture and photodisintegration reactions, than those usualy employed.

The tokamak is so far the most promising magnetic configuration for achieving a net production of fusion energy. The D-T fusion reactions result in 3.5 MeV alpha-particles, which may destabilize Alfvén eigenmodes through wave-particle interaction. These instabilities redistribute the alpha-particles from the central region of the plasma towards the edge, where they are thermalized, and hence result in a reduced heating efficiency. The high-energy alpha-particles may even be thrown out of the plasma and may damage the wall. To investigate the destabilization of Alfvén eigenmodes by high-energy ions, ion cyclotron resonance heating (ICRH) and neutral beam injection (NBI) are often used to create a high-energy tail on the distribution function. The ICRH does not only produce high-energy anisotropic tails, it also decorrelates the wave-particle interaction with the Alfvén eigenmodes. Without decorrelation of the wave-particle interaction an ion will undergo a superadiabatic oscillation in phase space and there will be no net transfer of energy to the mode. For the thermal ions the decorrelation from collisions dominates while for the high-energy ions the decorrelation from ICRH dominates. As the unstable modes grow up, the gradients in phase space, which drive the mode, are reduced, resulting in a weaker drive. The dynamics of the system becomes non-linear due to a continuous restoration of the gradients by D-T reactions and ICRH. In this thesis the non-linear dynamics of toroidal Alfvén eigenmodes (TAEs) during ICRH has been investigated using the SELFO code. The SELFO code, which calculates the distribution function during ICRH self-consistently using a Monte-Carlo metod, has been upgraded to include interactions with TAEs. The fast decay of the mode amplitude as the ICRH is switched off, which is seen in experiments, as well as the oscillation of the mode amplitude as the distribution function is repetetively built up by the ICRH and flattened by the TAE has been reproduced using numerical simulations. In the presence of several unstable modes the dynamics become more complicated. The redistribution of an alpha-particle slowing down distribution function as well as the reduced heating efficiency in the presence of several modes has also been investigated. / QC 20100628

According to classical linearized resistive magnetohydrodynamics theory, pressuredriven modes are unstable in the reversed-field pinch (RFP) due to unfavorable magnetic field line curvature. The result is based on the assumption of an adiabatic energy equation where anisotropic thermal conduction effects are ignored as compared to convection and compression. In this thesis the effects of heat conduction in the energy equation have been studied. We have examined these effects on the linear stability of pressure-driven resistive modes using boundary value theory (Δ´ ) and a novel initial-value full resistive MHD code employing the Generalized Weighted Residual Method (GWRM). In the Δ´ method, a shooting technique is employed by integrating from the resistive layer to boundaries. The GWRM method, on the other hand, is a time-spectral Galerkin method in which the fully linearized MHD equations are solved. For detailed computations, efficiency requires the temporal and spatial domains to be divided into subdomains. For this purpose, a number of challenging test cases including linearized ideal MHD equations are treated. Numerical and analytical investigations of equilibria reveal that thermal conduction effects are not stabilizing for reactor relevant values of Lundquist number, S0, and normalized pressure, βθ, for tearing-stable plasmas. These studies show that growth rate scales as  γ~_ S0−1/5 , which is weaker than for the adiabatic case, γ~_ S0−1/3. A numerical study of optimized confinement for an advanced RFP scenario including ohmic heating and heat conduction, is also part of this thesis. The fully nonlinear resistive MHD code DEBSP has been employed. We have identified, using both Δ´ and GWRM methods, that the observed crash of the high confinement is caused by resistive, pressure-driven modes. / <p>QC 20130503</p>

Made available in DSpace on 2014-10-09T12:53:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:27Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:53:58Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:27Z (GMT). No. of bitstreams: 0 / A pesquisa e o desenvolvimento de sistemas passivos de resfriamento de emergência são necessários para os sistemas termo-nucleares de nova geração. Algumas informações fundamentais sobre a operação desses sistemas requerem a pesquisa de alguns processos relativos à circulação natural, principalmente em condições de escoamento bifásico envolvendo processos de condensação na presença não-condensáveis, pois muitas situações encontradas são novas. A bancada experimental de circulação natural (BCN) foi utilizada para a realização de testes com diversas concentrações de não-condensáveis e níveis de potência. O não-condensável presente no circuito diminui a taxa de transferência de calor para o secundário do trocador de calor, causando baixo desempenho do trocador de calor. A presença de altas concentrações de não-condensáveis no trocador de calor propicia elevadas variações de pressão, decorrentes do processo de condensação abrupto, determinando a inversão da vazão e de fortes vibrações e esforços nas tubulações do circuito. A concentração inicial de não-condensável e a geometria do circuito, na entrada do trocador de calor, determinam o estabelecimento de transitórios com escoamento bifásico. A BCN foi modelada com o código computacional de Análise de Acidentes e Termo-Hidráulica RELAP5/MOD3.3 e, os valores calculados foram comparados com os dados experimentais, apresentando boa concordância para menores concentrações de ar. Os valores calculados para maiores concentrações de não-condensável foram satisfatórios após o circuito ter atingido a temperatura de saturação no aquecedor elétrico. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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.

Supernovae (SNe) and more specifically Core-Collapsed SNe (CC SNe) are signatures of on-going star formation (SF), and higher star formation rates. In this project, we perform a study of all SNe ever discovered inside a specific type of galaxy: a type-1 Active Galactic Nucleus (AGN1). We calculate the SN detection fraction for CC SNe and thermonuclear SNe in AGN1. In AGN1, inclination of the host galaxy and the radial distance of the SN to the center of the galaxy are displayed. As a second goal, we gather all SNe from the OpenSN catalogue found close to an AGN1, classify them and compare them with the full sample of OpenSN catalogue host galaxies. Results:We found and calculated the SN detection fraction of AGN1s. We found 16 SNe exploding in 13 different AGN1 host galaxies. The CC/Ia SN ratio is ~ 0.78. Comparing by similar morphology, the AGN1-host galaxies with all the host galaxies from OpenSN, we see that the detection fractions are higher in spiral AGN1 hosts than in normal spiral galaxies, but the difference is not significant (~ 0.4\sigma) to be considered.

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...