Dissertations / Theses on the topic 'Plasma heating in steelmaking'

A room temperature water model of a tundish was design, constructed and operated. The model was equipped with a steam heating system that simulates that simulates the tundish plasma heating systems operated by some of the more modem continuous casting plants. Similarity between steam heating in the water model and plasma heating in the tundish has been established. A dimensionless criterion was developed to validate the simulation experiments and its represented by the plasma heating number. Using this similarity criterion plasma heating can be simulated by steam heating in an appropriately designed water model. A theoretical dispersion model has been formulated for the flow through the tundish and the parameters in this model determined from the results obtained from residence time distribution measurements. A conductivity method was used, a highly conducting species being injected at the inlet point and changes in conductivity monitored at the exit. Measurements were also made of the changes in temperature at the exit resulting both from changes in temperature of the inlet stream and from the use of steam heater system. A stable inverse heat conduction method has been developed in which the measured and estimated temperature are analysed in terms of a steady components of short duration. A finite difference method has been used to predict the effect on a thermocouple temperature of the deviatory components of the liquid steel temperature. The incorporation of these predictions into look-up tables has allowed an algorithm to be developed thet can deduce the current deviatory component of the steel temperature from the thermocouple response.

The initial stage of the work was a study of an 80 tonne industrial furnace, taking observations, panel water temperature data and samples of slag layers from the sidewalls. This resulted in a simple model of layer formation which explained the observed structures, and also the effect of slag layer thickness on heat losses was examined. However, the complexity and variety of structures found were such that a full series of direct thermal conductivity measurements was deemed impractical, and so a theoretical model to calculate the thermal conductivity of complex structures from the thermal conductivities of it s components was developed. Other aspects of heat transfer both within the furnace and from the furnace interior to the water cooling were also explored. In order to obtain a reliable value of thermal conductivity for the slag component of layer structures, a technique was developed to measure the thermal conductivity of the slag. This consisted of firstly determining a viable route for the production of homogenous samples, followed by the design, construction and refinement of an experimental measuring rig. After a large number of preliminary measurements, a series of thermal conductivity values at temperatures between 300 and 800 °C were measured using operating conditions calibrated against a heat storage brick sample of known thermal conductivity. These results were used to provide the data for the theoretical thermal conductivity model, which was then applied to real structures for which thermal data was available. Comparison of the results showed good correlation. Finally, in the appended case study, the heat loss calculation was applied for various furnace situations to identify the potential heat loss savings that could be achieved by controlling the slag layer thickness and structure, and the financial implications.

Tesis para optar al grado de Magíster en Ciencias, Mención Física
Los plasmas son comunes en diferentes sistemas astronómicos. Una parte importante de estos plasmas están en el régimen no colisional, en que el camino libre medio de las partículas que lo componen es más grande que el tamaño del sistema. Un ejemplo de este tipo de objetos es el disco de acreción que se encuentra en las cercanías del agujero negro ubicado en el centro de la Vía Láctea, Sagitario A* (Sgr A*). Por su baja colisionalidad, se espera que el plasma en Sgr A* no siga una distribución de Maxwell-Boltzmann. Además, por la mayor eficiencia radiativa de los electrones, es también esperable que estos tengan menor temperatura que los iones. El grado en que se calientan los electrones en un sistema no colisional, así como su espectro de energía, tienen importantes consecuencias observacionales. Existen diversos mecanismos que pueden transferir energía a los electrones. Entre ellos están: reconexión magnética, interacción onda-partícula, y viscosidad anisotrópica. En esta tesis nos enfocamos en el calentamiento de electrones por medio de la interacción onda partícula y por calentamiento viscoso. Para ello realizamos simulaciones ``particle-in-cell'' (o PIC) de un plasma no colisional, magnetizado y sujeto a un cizalle permanente. Este cizalle produce una amplificación del campo magnético, obteniéndose así una anisotropía de presión en las particulas, debido a la invarianza adiabatica de su momento magnetico. Esta anisotropía produce inestabilidades cinéticas en el plasma, las que propagan ondas en escalas del radio de Larmor de las partículas. Algunos ejemplos relevantes para nuestro estudio son las inestabilidades de whistler e ion-ciclotrón. Estas inestabilidades pueden resonar preferentemente con los electrones e iones, respectivamente, otorgando o quitando energía a las partículas. Realizamos simulaciones con moderadas razones de masa entre iones y electrones, para estudiar a los electrones en el régimen cinético. Consideramos consistentemente el régimen no-lineal y cuasi-estacionario de las inestabilidades. Estudiamos el calentamiento de los electrones, y se encontró que estos se calientan principalmente por viscosidad. Sin embargo, se encontró un calentamiento extra, el que es transferido desde los iones a los electrones debido a la interacción de estos últimos con las ondas ion-ciclotrón (las que a su vez son principalmente producidas por los iones). Este calentamiento extra aumenta con la magnetización y disminuye al aumentar la razón de masa y la temperatura de los iones. Además, la componente no térmica del espectro de energía de los electrones se ve fuertemente modificada cuando el radio de Larmor de estos es similar al de los iones. Esta componente no térmica se asemeja bastante a lo que se infiere de observaciones de sistemas como Sgr A*. Nuestro trabajo nos permitió entonces encontrar condiciones que facilitan el calentamiento y aceleración no térmica de electrones debido a la transferencia de energía entre iones y electrones en plasmas no colisionales.

In this work techniques for heating the fusion reactor ITER to thermonuclear temperatures, over 100 million kelvin, is investigated. The temperature is numerically computed for different heating configurations. The heat leakage is modeled to occur only via diffusion. The diffusion is assumed to be a combination of Bohm and gyro-Bohm diffusion. Basic conditions for a fusion reactor has been studied. The power needed for the different heat sources for the plasma to ignite is computed. Plots of the temperature profiles are included in the results together with plots showing the Q-value dependency on the power and the major radius.

Firstly, we present reviews of the background atomic, magnetohydrodynamic, and solar, physics involved in the analysis of the problem. We proceed to produce a time dependent code to calculate the Ionisation state distribution of Iron and of Argon, using some of the recent data for Ionisation coefficients by Arnaud & Raymond (1992), and Fournier et al. (1997, 1998). We also look at some data for the excited ionised states using the Chianti database amongst others. Taking the engine developed, we continue by applying it to a three stage nanoflare simulation for the heating, spanning a 2000km range. This model is drawn from various previous models developed in the literature. We look for the indications of the non Local Thermodynamic Equilibrium (LTE) processes via the concept of "signature ions". By this we mean the presence of highly charged ions which would not be expected if the temperature were simply constant and everywhere was in LTE. We make a calculation of the actual experimental line of sight results that we would obtain, if we were to take Emission Measure calculations to ascertain the Ionisation distribution within the Solar Atmosphere. We also take a look at the problem of Diagnostics based on Emission Measure Analysis, and investigate the fundamental nature of the Inversion Problem. Simply stated, it is difficult to obtain the differential emission measure (DEM) of the Transition Region because the only information that we have available to us is the intensity of spectral lines emitted from the Sun. This consists of the integral of the DEM convolved with a function representing the physics of the transition. The problems associated with the inversion of the integral, form much of the discussion together with the philosophical implications of using phenomenology as an alternative.

The terrestrial foreshock, the area upstream of, and magnetically connected to, the bow shock is a complex system in which the turbulent, supersonic and superalfvénic solar wind encounters the Earth’s magnetosphere. As a result, particle populations stream sunwards against the solar wind flow, creating a kinetic two-stream instability that leads to a variety of linear and nonlinear plasma processes. Foreshock plasma is collisionless, and the instability supports a variety of ultra-low frequency (ULF) modes. A statistical technique, based on categorizing wavenumber-frequency pairs by their associated power, is used to determine the dispersion relations for ULF modes in a number of case studies using magnetic field data from two-point measurements of the Cluster mission. Sunward-propagating fast magnetosonic and beam resonant modes are identified, as well as Alfvén modes propagating both sunwards and anti-sunwards. The fast magnetosonic modes are advected towards the Earth by the solar wind, and due to a cubic nonlinearity, steepen into sharply peaked waves. Three examples of these nonlinear wavetrains are compared to solutions of the derivative nonlinear Schrödinger equation, and are found to be in good agreement. The impact of the waves on the form of the pseudopotential, a quantity related to core plasma parameters, is also discussed. Wave-wave interactions are investigated for a case study of Cluster data, with a focus on energy transfer between ULF modes and a band of frequencies centred at 1Hz. Evidence for three-wave processes, formed by quadratic nonlinearities that interact between triads of frequencies that satisfy the frequency (f1 + f2 + f3) and wavenumber (k1 + k2 + k3) resonance conditions, is presented. Evidence for four wave processes in the same interval is also discussed.

Equations are derived to describe the evolution of an electron distribution function under the action of electromagnetic instabilities in a non-uniform plasma using an extension of the quasilinear theory of Kennel and Engelmann. Variations in both the electron density and temperature and the background magnetic field are taken into account. These equations are simplified in the limit of small electron beta so that an electrostatic approximation is justified. Methods are then presented which allow the solution of these equations (or, in principle, the more complex electromagnetic equations). In particular, a method of solving the kinetic dispersion relation for an arbitrary background (first-order) distribution function with the minimum of additional assumptions and approximations is described in detail. The electrostatic equations are solved for a number of different cases in order to study the action of the modified two stream instability on the electron distribution function. Throughout, realistic values of the ratios of electron to ion mass and electron plasma to cyclotron frequency ratio are used. The applications to collisionless plasma shock waves are discussed, and it is found that the modified two stream instability can produce the (relatively small) amounts of electron heating observed at quasi-perpendicular terrestrial bow shocks, and the flat-topped electron distribution functions seen to evolve. Extensions to the model which would greatly improve its applicability and accuracy, as well as the amount of computational effort required, are discussed.

Shock waves are ubiquitous in space and astrophysics. Shocks transform directed particle flow energy into thermal energy. As the major part of space is a collisionless medium, shocks in space physics arises through wave-particle interactions with the magnetic field as the main contributor.The heating processes are scale dependent. The large scale processes governs the ion heating and is well described by magnetohydrodynamics. The small scale processes governs the electron heating lies within the field of kinetic plasma theory and is still today remained disputed. A step towards the answer for the small scale heating would be to measure the scale, in order to relate it to a known instability or other small scale processes.The multi-spacecraft NASA MMS spacecraft carries several high resolute particle and field instruments enabling almost instantaneous 3D particle measurements and accurate measurements of the magnetic field. Also the separation between the four MMS spacecraft is as small as < 8km for a certain mission phase. This allows for new approaches when determining the scale which for shocks has not been possible before when using data from previous multi-spacecraft missions with spacecraft separation much larger. The velocity of the shock is large compared to the spacecraft,thus the shock width cannot be directly measured by each spacecraft. Either a constant velocity has to be estimated or we could use gradients of a certain parameter between the spacecraft as the shock flows over them. The usage of gradients is only possible with MMS as all the spacecraft could for MMS be within the shock simultaneously. The change for a parameter within the shockis assumed to be linear between the spacecraft and measurements. It is also assumed that the gradient of the parameter maximizes in the shock normal direction. Using these assumptions two methods have been developed. They have the same working principles but are using two or four spacecraft for linear estimation at each measurement point. From the gradient and parametric data the shock ramp width could then be found. The parameter used in this thesis is the electron temperature. The methods using one, two and four spacecraft were tested using electron temperature data from different shock crossings. Two problems with the gradient methods were found from the results, giving false data for certain time spans. To avoid these problems, the scale of the electron temperature gradient was determined for roughly half the shock ramp. It was found using the two and four spacecraft methods that an assumption of constant velocity for the shock speed is an uncertain assumption. The shock speed varies over short time scales and in the shock crossings analysed the constant velocity estimations were generally overestimated. From the two and four spacecraft methods roughly half of the temperature rise in the shock ramp occurred over 10.8km or 12.4 lpe. This is almost a factor of two greater than previous scale estimates using Cluster data and a multi-spacecraft timing method for shock speed estimation.From the results it is concluded that the methods when using gradients between spacecraft has some restrictions. They can only be used for MMS data, requires quasi-perpendicular high Mach number and will give false results if the temperature is disturbed by interacting hot plasma clouds. However, even though we have these limitations for the tested gradient methods, they were found better and more reliable compared to previous methods for shock scaling.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2001.
Includes bibliographical references (p. 281-289).
Remote sensing techniques employed to diagnose ionospheric modification experiments are intrinsically ambiguous, uncorrelated with "ground truth." To overcome this limitation, laboratory experiments are performed in the model ionosphere of the Versatile Toroidal Facility (VTF). The VTF contains a thermionically produced, weakly magnetized ( wce < wpe) background plasma of either hydrogen or argon. The HF "pump" wave of ionospheric experiments is modeled by 2.45 GHz microwaves, launched perpendicular to the magnetic field and the density gradient of the VTF in the ordinary mode. The peak plasma density is several times greater than the critical density (nc ~/= 7.4xI0 16 m-3 ), and the microwaves reflect, forming a standing wave Airy pattern. Wave spectra produced near reflection are measured using a miniature double probe and microwave receiver along with a fast oscilloscope. This combination is capable of simultaneously measuring spectra in two 250 MHz bands, one near DC and the other near the 2.45 GHz pump, to μs resolution. In addition, absolute electric field strengths and wavenumber spectra can be estimated. To explore the extent to which the VTF experiments simulate ionospheric heating, similarity rules are derived from the governing equations and applied to the two plasmas. A set of ten dimensionless parameters results, six of which match satisfactorily between the two plasmas. Three others can be neglected, leaving only one unmatched parameter: the ratio T/Ti, which in the VTF is about 12 and in the ionosphere is near unity. Consideration of boundary conditions limits the scope of the simulation to the first Airy maximum. The main observational results of VTF heating experiments are: (1) Langmuir wave sidebands both up- and down-shifted from the pump frequency that decrease monotonically to the noise floor in tens of MHz, (2) lower hybrid waves in a broad band from 35 - 150 MHz, with maximum power occurring at 50 - 90 MHz, (3) both Langmuir and lower hybrid waves appear in bursts of duration and period in the 2- 100 ms range, depending upon radius, (4) Langmuir and lower hybrid bursts are anti-correlated at the edge of the plasma but become uncorrelated in the core, and (5) the electric field, both of the pump and the plasma sidebands, varies by a factor of 100 in a burst period, from 1.3 to 130 kV /m for the pump (expected: 10.8 kV/m). The main features of ionospheric heating were reproduced in these experiments: down- and up-shifted high frequency sidebands, extreme time-variability of electric field amplitude, large pump wave absorption, and significant electron heating. The observed spectral bursts suggest the concentration of electric field into small time-varying regions. The periods and parameter dependencies of the bursts resemble results of three-dimensional simulations of Langmuir turbulence. However, the upshifted Langmuir waves predicted by strong Langmuir turbulence (SLT) and nonlinear scattering theory are not observed in the VTF. A consistent account of the VTF observations is obtained by combining the caviton collapse cycle of SLT and the parametric production of lower hybrid waves by energetic Langmuir waves. As the high frequency electric field concentrates in cavitons, the threshold for the Langmuir decay instability is exceeded, generating lower hybrid waves in anti-correlated bursts. Because of the similarity of the VTF experiments to ionospheric heating, the observation of lower hybrid wave production during heating may also be borne out by future field experiments with diagnostics capable of viewing field-aligned modes.
by Nathan E. Dalrymple.
Sc.D.

The problem of how the Sun's corona is heated is of central importance to solar physics research. In this thesis we model three main areas. The first, annihilation, is a feature of non-ideal MHD and focusses on how magnetic field of opposite polarity meets at a null point and annihilates, after having been advected with plasma toward a stagnation point in the plasma flow. Generally, the null point of the field and the stagnation point of the flow are coincident at the origin, but in chapter 2 a simple extension is considered where an asymmetry in the boundary conditions of the field moves the null point away from the origin. Chapter 3 presents a model of reconnective annihilation in three dimensions. It represents flux being advected through the fan plane of a 3D null, and diffusing through a thin diffusion region before being annihilated at the spine line, and uses the method of matched asymptotic expansions to find the solution for small values of the resistivity. The second area of the thesis covers null collapse. This is when the magnetic field in close proximity to a null point is disturbed, causing the field to fold up on itself and collapse. This is a feature of ideal MHD, and causes a strong current to build up, allowing non-ideal effects to become important. When using linearised equations for the collapse problem, we are in fact looking at a linear instability. If this instability initiates a collapse, this is only a valid model until non-linear effects become important. By talking about collapse in chapters 4 and 5 (as it is talked about in the literature), we mean that the linear instability initiates collapse, which in principle, non-linear effects could later stop. Chapter 4 introduces a two-dimensional model for collapse, using the ideal, compressible, linearised MHD equations. It is a general solution in which all spatially linear nulls and their supporting plasma flows and pressure gradients can be checked for susceptibility to collapse under open boundary conditions. Chapter 5 uses the model introduced in chapter 4 to investigate the collapse of three-dimensional, potential nulls (again, spatially linear) for all possible supporting plasma flows and pressure gradients. Using this model, all nulls under consideration are found to collapse and produce large currents, except for a group of 2D O-type nulls supported by highly super-Alfvenic plasma flows. The third area of this thesis involves numerically simulating a model of heating by coronal tectonics (Priest et al, 2002). A simple magnetic field is created and the boundary is driven, also in a simple manner. Current sheets which scale with grid resolution are seen to build up on the quasi-separatrix layers, and there is some evidence of magnetic reconnection.

Thesis (M.S.)--West Virginia University, 2008.
Title from document title page. Document formatted into pages; contains viii, 45 p. : ill. Includes abstract. Includes bibliographical references (p. 43-45).

Thesis (Ph. D.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains v, 127 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 94-98).

A dusty plasma is a mixture of electrons, ions, neutral gas atoms, and small particles of solid matter (dust). In a dusty plasma produced in the laboratory, dust particles gain a large electric charge from the other charged species, so that their interparticle interactions can be very strong. Frequently, the average interparticle potential energy is higher than the thermal kinetic energy of the dust particles, and in this case, they constitute a strongly coupled plasma. As with all strongly coupled plasmas, the dust particles can behave like typical solids or liquids. In this thesis, I report the results of dusty plasma experiments that are focused on the behavior of liquids. I use a so-called two-dimensional (2D) dusty plasma that consists of only a single horizontal layer of dust particles. Tracking each particle with video microscopy and image analysis methods allows the calculation of important liquid properties, like the viscosity coefficient. In Chapter 2, I describe an improved laser heating method for producing liquid-like conditions in a 2D dusty plasma. Two laser beams are scanned across the dust layer in a new pattern to increase the kinetic energy of the particles and melt the ground state crystalline lattice. The new scanning pattern improves the randomness of the resulting particle motion so that it more closely resembles that of a liquid in a thermal equilibrium. In Chapter 3, I report a viscosity measurement in a dusty plasma that is unaffected by the complicating effects of temperature nonuniformities and shear thinning. This measurement is enabled by an addition to my experimental apparatus that I also detail here. I find the viscosity to be significantly higher than in previous measurements, which I attribute to the avoidance of shear thinning. In Chapter 4, I present measurements of viscosity using the Green-Kubo method, and compare the results to those of my previous measurement. I find that the two methods yield viscosity values that differ by about 60%, over the entire temperature range attained in the experiment. Possible sources of this difference are evaluated. Finally, in Chapter 5, I report the first experimental confirmation of a theoretical expression describing the decay of time autocorrelation functions. This theoretical expression fits experimentally calculated autocorrelation functions within error bars, especially at short times when a simple exponential decay fails. I also propose an intuitive description wherein an observed transition in the autocorrelation function is due to the onset of collisional scattering.

The sintering of aluminum nitride in a microwave induced plasma was investigated. The plasma furnace consisted of a quartz tube inserted into a waveguide connected to a 2450 MHz microwave generator. After evacuating the tube to about 1.33 mbar, nitrogen gas was introduced, generating a steady plasma. Processing parameters such as gas pressure, power level, and time were optimized to yield maximum densification of aluminum nitride. Sintering of pure and doped AlN compacts was performed in the nitrogen plasma at temperatures up to 2000 S C. Undoped specimens reached densities of only 81% theoretical, while densities in excess of 95% theoretical were achieved for yttria doped specimens in less than 15 minutes. Microstructural investigations revealed a smaller grain size in the plasma sintered specimens (about 2μ) than are present in conventionally sintered AlN (about 8μ).

Thesis (Ph. D.)--West Virginia University, 2002.
Title from document title page. Document formatted into pages; contains viii, 176 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada
Real-time transmission of airborne images to a ground station is highly desirable in many telemetering applications. Such transmission is often through an error prone, time varying wireless channel, possibly under jamming conditions. Hence, a fast, efficient, scalable, and error resilient image compression scheme is vital to realize the full potential of airborne reconnaisance. JPEG2000, the current international standard for image compression, offers most of these features. However, the computational complexity of JPEG2000 limits its use in some applications. Thus, we present a scalable low complexity coder (SLCC) that possesses many desirable features of JPEG2000, yet having high throughput. Continuous radio-wave telemetry is required during planned tests of directed-energy weapons systems in order to characterize in situ the effects of laser irradiation on different target materials. Unfortunately, the incident radiation can cause disruption of the radio signal during the directed-energy testing. Several phenomena associated with directed-energy impact can lead to communication path losses, such as ablation, charged particle emission, charring, and chemical changes in the target materials. Directed-energy impact on the target material leads to target heating and consequent ablation. In this paper, a numerical model has been developed to describe the laser induced ablation of metal surfaces. The model describes the absorption of the laser energy by the metal and the resulting temperature rise in the surface. This temperature rise then induces ablation of the target material. Results for an aluminum target irradiated with a KrF laser were obtained. Temperature profiles in the target material and surface temperature changes are presented along with the ablation rate as a function of time as the aluminum target is irradiated. This report presents results for cases when laser energy absorption by the plasma plume created above the surface is not significant.

Disorder-induced heating (DIH) is a nonequilibrium, ultrafast relaxation process that occurs when laser-cooled atoms are photoionized to make an ultracold plasma. Its effects dominate the ion motion during the first 100 ns of the plasma evolution. Using tools of atomic physics we study DIH with ns time resolution for different plasma densities and temperatures. By changing the frequency of the laser beam we use to probe the ions, we map out the time evolution of the velocity distribution. We can compare this to a fluorescence simulation in order to more clearly determine the relationship between the fluorescence signal and the velocity distribution. In this study we observe and characterize effects due to electron screening on the ions during the equilibration process.

Le Chauffage Cyclotron Ionique (ICRH) par des ondes dans la gamme 30-80MHz est couramment utilisé dans les plasmas de fusion magnétique. Excitées par par des réseaux phasés de rubans de courant à la périphérie du plasma, ces ondes existent sous deux polarisations. L’onde rapide traverse le bord ténu du plasma par effet tunnel puis se propage à son centre où elle est absorbée. L’onde lente, émise de façon parasite, existe seulement à proximité des antennes. Quelle puissance peut être couplée au centre avec 1A de courant sur les rubans? Comment les champs radiofréquence (RF) proches et lointains émis interagissent-ils avec le plasma de bord par rectification de gaine RF à l’interface plasma-paroi? Pour répondre simultanément à ces deux questions, en géométrie réaliste sur l’échelle spatiale des antennes ICRH, cette thèse a amélioré et testé le code numérique SSWICH (Self-consitent Sheaths and Waves for ICH). SSWICH couple de manière auto-cohérente la propagation des ondes RF et la polarisation continue (DC) du plasma via des conditions aux limites non-linéaires de type gaine (SBC) appliquées à l’interface plasma / paroi. La nouvelle version SSWICH-FW est pleine onde et a été développée en deux dimensions (toroïdale/radiale). De nouvelles SBCs couplant les deux polarisations d’ondes ont été obtenues et mises en œuvre le long de parois courbes inclinées par rapport au champ magnétique de confinement. Avec ce nouvel outil en l'absence de SBCs, nous avons étudié l'impact d'une densité décroissant continûment à l'intérieur de la boîte d'antenne en traversant la résonance hybride basse (LH). Dans les limites mémoire de notre poste de travail, les champs RF au-dessous de la résonance LH ont changé avec la taille de maille. Par contre spectre de puissance couplée n’a que très peu évolué, et n’était que faiblement influencé par la densité à l'intérieur de l'antenne. En présence de SBCs, les simulations SSWICH-FW ont identifié le rôle de l'onde rapide sur l’excitation de gaines RF et reproduit certaines observations expérimentales clés. SSWICH-FW a finalement été adapté pour réaliser les premières simulations 2D électromagnétiques et de gaine-RF de la machine plasma cylindrique magnétisée ALINE
Ion Cyclotron Resonant Heating (ICRH) by waves in 30-80MHz range is currently used in magnetic fusion plasmas. Excited by phased arrays of current straps at the plasma periphery, these waves exist under two polarizations. The Fast Wave tunnels through the tenuous plasma edge and propagates to its center where it is absorbed. The parasitically emitted Slow Wave only exists close to the launchers. How much power can be coupled to the center with 1A current on the straps? How do the emitted radiofrequency (RF) near and far fields interact parasitically with the edge plasma via RF sheath rectification at plasma-wall interfaces? To address these two issues simultaneously, in realistic geometry over the size of ICRH antennas, this thesis upgraded and tested the Self-consistent Sheaths and Waves for ICH (SSWICH) code. SSWICH couples self-consistently RF wave propagation and Direct Current (DC) plasma biasing via non-linear RF and DC sheath boundary conditions (SBCs) at plasma/wall interfaces. Its upgrade is full wave and was implemented in two dimensions (toroidal/radial). New SBCs coupling the two polarizations were derived and implemented along shaped walls tilted with respect to the confinement magnetic field. Using this new tool in the absence of SBCs, we studied the impact of a density decaying continuously inside the antenna box and across the Lower Hybrid (LH) resonance. Up to the memory limits of our workstation, the RF fields below the LH resonance changed with the grid size. However the coupled power spectrum hardly evolved and was only weakly affected by the density inside the box. In presence of SBCs, SSWICH-FW simulations have identified the role of the fast wave on RF sheath excitation and reproduced some key experimental observations. SSWICH-FW was finally adapted to conduct the first electromagnetic and RF-sheath 2D simulations of the cylindrical magnetized plasma device ALINE

Observations of modifications of the electron temperature in the F-region produced by powerful high-frequency waves transmitted in X-mode are presented. The experiments were performed during quiet nighttime conditions with low ionospheric densities so no reflections occurred. Nevertheless temperature enhancements of the order of 300-400K were obtained. The modifications found can be well described by the theory of Ohmic heating by the pump wave and both temporal and spatial changes are reproduced.  A brief overview of several different experimental campaigns at EISCAT facilities in the period from October 2006 to February 2008 are also given pointing out some interesting features from the different experiments. The main focus is then on the campaign during October 2006 and modifications of the electron temperature in the F-region.

Experiments on several tokamaks convincingly demonstrated that a deliberate seeding of selected impurities can have a positive effect on the plasma performance. On the one hand, a significant reduction of the head load on divertor plates, one of the main concerns by constructing a thermonuclear reactor, has been achieved due to the increase of edge radiation. On the other hand, in some devices impurity seeding has led to an improvement of the energy confinement and the so called radiation improved (RI) mode has been established with the same or even better confinement than in the H-mode. However, in order to make use of these positive impacts, the behaviour of seeded impurity has to be strictly controlled and such negative developments as the accumulation of impurity ions in the plasma core accompanied by a strong increase of the central radiation losses should be avoided.

Plasma heating by radio-frequency (RF) waves has been proven to be a useful tool to control the behaviour of puffed impurities. In order to asses the prospective of impurity control by RF waves in larger devices and under reactor conditions, proper modelling approaches have been developed. One of the important parameters, which should be evaluated, is the averaged energy or temperature of heated impurity ions. The latter determines, in particular, the power transported to the main species, and, thus, the heating efficiency. Besides, the temperature of impurity ions characterizes the intensity of particle losses for heated impurities. An approach to compute the impurity temperature under such conditions is elaborated. It is based on the construction of a hierarchy of approximate solutions to the impurity heat balance equation and takes into account that the density and, thus, the heat conductivity of heated ion species can change by many orders of magnitude with the position in the plasma. The developed method has been incorporated into 1D transport code RITM. Coupled with the full wave code TORIC, the particle and heat balances for impurity and main plasma species provide a self-consistent approach to model the ion cyclotron resonance heating (ICRH) scenario. The modelling of various heating scenarios for several tokamaks displays the impacts of impurity heating on the heat and particles transport and heating efficiency. To investigate the possibility of impurity control at the large tokamak the experiment on selective impurity heating in the mode conversion H/D plasma was prepared and carried out in the tokamak JET.

Doctorat en sciences, Spécialisation physique
info:eu-repo/semantics/nonPublished

The solar wind undergoes significant heating as it propagates away from the Sun; the exact mechanisms responsible for this heating are not yet fully understood. We present for the first time a statistical test for one of the proposed mechanisms: stochastic ion heating. We use the amplitude of magnetic field fluctuations near the proton gyroscale as a proxy for the ratio of gyroscale velocity fluctuations to perpendicular (with respect to the magnetic field) proton thermal speed, defined as epsilon(p). Enhanced proton temperatures are observed when epsilon(p) is larger than a critical value (similar to 0.019-0.025). This enhancement strongly depends on the proton plasma beta (beta parallel to(p)); when beta parallel to(p) << 1 only the perpendicular proton temperature T-perpendicular to increases, while for beta parallel to(p) similar to 1 increased parallel and perpendicular proton temperatures are both observed. For epsilon(p) smaller than the critical value and beta parallel to(p) << 1 no enhancement of Tp is observed, while for beta parallel to(p) similar to 1 minor increases in T-parallel to are measured. The observed change of proton temperatures across a critical threshold for velocity fluctuations is in agreement with the stochastic ion heating model of Chandran et al. We find that epsilon(p) > epsilon(crit) in 76% of the studied periods, implying that stochastic heating may operate most of the time in the solar wind at 1 au.

Negli ultimi decenni, la ricerca e lo sviluppo di nuove fonti di energia sono state oggetto di crescente interesse scientifico. In particolare, la fusione nucleare potrebbe essere la soluzione al problema energetico mondiale. ITER è attualmente il più grande esperimento di fusione nucleare in via di costruzione. Situato nel sud della Francia, sarà il più grande tokamak costruito al mondo con l'obiettivo di produrre 500 MW di potenza dai 50 MW di potenza fornitagli. Diversi metodi di riscaldamento del plasma sono in via di sviluppo per poter scaldare il core del plasma a temperature dell'ordine dei 15 keV. Tra questi, l'iniezione di fasci neutri è uno dei più importanti. Il progetto PRIMA, costituito dagli esperimenti SPIDER e MITICA in via di costruzione al Consorzio RFX a Padova, si pone come obiettivo lo studio dei futuri iniettori di fasci neutri di ITER. L'esperimento NIO1, anch'esso situato al Consorzio RFX, è una relativamente piccola sorgente a radio frequenza RF di ioni negativi, nato con l'obiettivo di caratterizzare la fisica delle sorgenti di ioni nell'ottica dei futuri utilizzi negli iniettori di fasci neutri, quali lo stesso MITICA. Questo lavoro di tesi, nato da una collaborazione tra i Laboratori Nazionali di Legnaro (LNL) e il Consorzio RFX, caratterizza il fascio di ioni negativi di NIO1. I dati raccolti durante le campagne sperimentali sono stati analizzati e confrontati, per testare le performance della nuova griglia di estrazione installata su NIO1 a maggio 2017. La caratterizzazione è stata fatta in diversi modi: confrontando qualitativamente i dati raccolti dalle varie diagnostiche; ricostruendo tomograficamente l'immagine dei 9 beamlets tramite i dati raccolti dalle telecamere; caratterizzando il plasma formatosi in seguito alla propagazione del fascio nel gas di fondo, tramite il confronto con i dati sperimentali e quelli ottenuti da una simulazione numerica Particles-In-Cell PIC.

Recently, experimental observations have shown that radar echoes from the irregularity
source region associated with mesospheric dusty space plasmas may be modulated by radio wave heating with ground-based ionospheric heating facilities. These experiments show great promise as a diagnostic for the associated dusty plasma in the Near-Earth Space Environment which is believed to have links to global change. This provides an alternative to more complicated and costly space-based observational approaches to investigating these layers. This dissertation seeks to develop new analytical and computational models to investigate fundamental physics of the associated dusty plasmas as well as utilize experimental observations during High Frequency HF ground-based heating experiments to develop practical techniques for diagnosing these dusty plasma layers.
The dependency of the backscattered signal strength (i.e. Polar Mesospheric Summer Echoes PMSEs) after the turn-on and turn-off of the radio wave heating on the radar frequency is an unique phenomenon that can shed light on the unresolved issues associated with the basic physics of the natural charged mesospheric dust layer. The physical process after turn-on and turn-off of radio wave heating is explained by competing ambipolar diffusion and dust charging processes. The threshold radar frequency and dust parameters for the enhancement or suppression of radar echoes after radio wave heating turn-on are investigated for measured mesospheric plasma parameters. The effect of parameters such as the electron temperature enhancement during radiowave heating, dust density, dust charge polarity, ion-neutral collision frequency, electron density and dust radius
on the temporal evolution of electron irregularities associated with PMSE is investigated.
The possibility of observing the turn-on overshoot (enhancement of radar echoes after the
radiowave turn-on) in the high frequency HF radar band is discussed based on typical mesospheric
parameters. It has been shown that predicted enhancement of electron irregularity
amplitude after heater turn-on at HF band is the direct manifestation of the dust charging
process in the space. Therefore further active experiments of PMSEs should be pursued
at HF band to illuminate the fundamental charging physics in the space environment to
provide more insight on this unique medium. Preliminary observation results of HF PMSE
heating experiment with the new 7.9 MHz radar at the European Incoherent Scatter EISCAT
facility appear promising for the existence of PMSE turn-on overshoot. Therefore, future
experimental campaigns are planned to validate these predictions.
Computational results are used to make predictions for PMSE active modification experiments at 7.9, 56, 139, 224 and 930MHz corresponding to existing ionospheric heating facilities. Data from a 2009 very high frequency VHF (224 MHz) experiment at EISCAT
is compared with the computational model to obtain dust parameters in the PMSE. The
estimated dust parameters as a result of these comparison show very reasonable agreement to dust radius and density at PMSE altitudes measured during a recent rocket experiment providing validation to the computational model.

The first comprehensive analytical model for the temporal evolution of PMSE after heater
turn-on is developed and compared to a more accurate computational model as a reference.
It is shown that active PMSE heating experiments involving multiple observing frequencies
at 7.9 (HF), 56, and 224 MHz (VHF) may contribute further diagnostic capabilities since
the temporal evolution of radar echoes is substantially different for these frequency ranges.
It is shown that conducting PMSE active experiments at HF and VHF band simultaneously
may allow estimation of the dust density altitude profile, dust charge state variation during
the heating cycle, and ratio of electron temperature enhancement in the irregularity source
region. These theoretical and computational models are extended to study basic physics of the evolution of relevant dusty plasma instabilities thought to play an important role in irregularity production in mesospheric dust layers. A key focus is the boundary layer of these charged dust clouds. Several aspects of the cloud\'s structure (thickness of boundary layer, average particle size and density, collisional processes, and cloud expansion speed) and the ambient plasma are varied to determine the effect of these quantities on the resulting irregularities.
It was shown that for high collision frequencies, the waves may be very weakly excited (or
even quenched) and confined to the boundary layer. The excited dust acoustic waves inside
the dust cloud with frequency range of 7-15Hz and in the presence of electron bite-outs is
consistent with measured low frequency waves near 10 Hz by sounding rocket experiments
over the past decade. The observed radar echoes associated with the artificially created dust
clouds at higher altitudes in the ionosphere including space shuttle exhaust and upcoming
active space experiments in which localized dust layers will be created by sounding rockets
could be related to the excited acoustic waves predicted.
Finally, variation of spatial structures of plasma and dust (ice) irregularities in the PMSE
source region in the presence of positively charged dust particles is investigated. The correlation and anti-correlation of fluctuations in the electron and ion densities in the background plasma are studied considering the presence of positive dust particle formation. Recent rocket payloads have studied the properties of aerosol particles within the ambient plasma environment in the polar mesopause region and measured the signature of the positively charged particles with number densities of (2000 cm"3) for particles of 0.5-1 nm in radius.
The measurement of significant numbers of positively charged aerosol particles is unexpected from the standard theory of aerosol charging in plasma. Nucleation on the cluster ions is one of the most probable hypotheses for the positive charge on the smallest particles. The utility being that it may provide a test for determining the presence of positive dust particles.
The results of the model described show good agreement with observed rocket data. As an
application, the model is also applied to investigate the electron irregularity behavior during
radiowave heating assuming the presence of positive dust particles. It is shown that the
positive dust produces important changes in the behavior during Polar Mesospheric Summer Echo PMSE heating experiments that can be described by the fluctuation correlation and anti-correlation properties.
The second part of this dissertation is dedicated to Stimulated Electromagnetic Emissions SEEs produced by interaction of high power electromagnetic waves in the ionosphere. Nearearth ionospheric plasma presets a neutral laboratory for investigation of nonlinear wave phenomena in plasma which can not be studied in the laboratory environment due to the effect of physical boundary conditions. This process has been of great interest due to the
important diagnostic possibilities involving ability to determine mass of constitutive ions in
the interaction region through measurements of various gyro-frequencies. Objectives include
the consideration of the variation of the spectral behavior under pump power, proximity to
the gyro-harmonic frequency, and beam angle. Also, the relationship between such spectral
features and electron acceleration and creation of plasma irregularities was an important
focus.
Secondary electromagnetic waves excited by high power electromagnetic waves transmitted
into the ionosphere, commonly know as Stimulated Electromagnetic Emissions SEEs,
produced through Magnetized Stimulated Brillouin Scatter MSBS are investigated. Data
from two recent research campaigns at the High Frequency Active Auroral Research Program
facility HAARP is presented in this work. These experiments have provided additional
quantitative interpretation of the SEE spectrum produced by MSBS to yield diagnostic measurements of the electron temperature in the heated ionosphere. SEE spectral emission lines corresponding to ion acoustic IA and electrostatic ion cyclotron EIC modes were observed with a shift in frequency up to a few tens of Hz from radio waves transmitted near the third harmonic of the electron gyro-frequency 3fce. The threshold of each emission line has been measured by changing the pump wave amplitude. The experimental results aimed to show the threshold for transmitter power to excite IA waves propagating along the magnetic field lines as well as for EIC waves excited at oblique angles relative to the background magnetic field. A full wave solution has been used to estimate the amplitude of the electric field at the interaction altitude. The estimated growth rate using the theoretical model is compared with the threshold of MSBS lines in the experiment and possible diagnostic information for the background ionospheric plasmas is discussed. Simultaneous formation of artificial field aligned irregularities FAIs and suppression of the MSBS process is investigated. Recently, there has been significant interest in ion gyro-harmonic structuring the Stimulated Electromagnetic Emission SEE spectrum due to the potential for new diagnostic information available about the heated volume and ancillary processes such as creation of artificial ionization layers. These relatively recently discovered emission lines have almost exclusively been studied for second electron gyro-harmonic heating. The first extensive systematic investigations of the possibility of these spectral features for third electron gyro-harmonic heating are provided here. Discrete spectral features shifted from the transmit frequency ordered by harmonics of the ion gyro-frequency were observed for third electron gyro-harmonic heating for the first time at a recent campaign at a High Frequency Active Auroral Research Program Facility HAARP. These features were also closely correlated with a broader band feature at a larger frequency shift from the transmit frequency known as the Downshifted Peak DP. The power threshold of these spectral features was measured, as well as their behavior with heater
beam angle, and proximity of the transmit frequency to the third electron gyro-harmonic frequency. Comparisons were also made with similar spectral features observed during 2nd
electron gyro-harmonic heating during the same campaign. A theoretical model is provided
that interprets these spectral features as resulting from parametric decay instabilities in
which the pump field ultimately decays into high frequency upper hybrid/electron Bernstein
and low frequency neutralized ion Bernstein IB and/or obliquely propagating ion acoustic
waves at the upper hybrid interaction altitude. Coordinated optical and SEE observations
were carried out in order to provide a better understanding of electron acceleration and precipitation
processes. Optical emissions were observed associated with SEE gyro-harmonic
features for pump heating near the second electron gyro-harmonic during the campaign. The
observations affirm strong correlation between the gyro-structures and the airglow.
Ph. D.

Neutron emission spectra, measured with the time of flight spectrometer TOFOR, at the joint European torus (JET) are presented in this thesis. TOFOR has been in use since 2005, routinely measuring the neutron emission from JET plasmas. The work in the thesis mainly concerns the modeling of the signatures in the neutron spectrum that reveal different parts of the fuel ion distribution, such as the thermal bulk plasma as well as energetic ions from neutral beam and ion cyclotron heating. Parametric models of the signatures, using plasma parameters as input, are employed to generate trial neutron spectra. The parameters, such as the fuel ion temperature or the fast ion distribution function, are deduced by iteratively fitting the trial spectra to the measured data. Measurements with TOFOR have been made and the models were applied. The studies are mainly on neutrons from d(d, n)3 He reactions(DD), although the emission from reactions with the plasma impurity 9 Be and triton burn up is covered as well. This has allowed for detailed studies of e.g. the physics ICRF heating as well as the interactions between energetic ions and plasma instabilities, such as toroidal Alfvé Eigenmodes.

Les ondes de surface ont été observées pour la première fois par Wood en 1902 qui note des anomalies dans le spectre de diffraction d'une lumière continue sur un réseau métallique. Pour certaines longueurs d'onde, le spectre diffracté présente des lignes noires que Fano interprète quelques années plus tard (1941) comme dues à l'excitation d'ondes de surface. De façon analogue, on peut exciter par laser de façon résonante une onde plasma de surface à la surface d'un plasma sur-dense créé par interaction laser-solide, si les conditions d'excitation de l'onde sont satisfaites. L'onde de surface se propage le long de l'interface plasma-vide et se caractérise par un champ électrique résonant haute-fréquence localisé. Dans ce travail, la dynamique du plasma et les champs associés à l'excitation par laser de l'onde de surface sont décrits numériquement avec des simulations bidimensionnelles Particule-In-Cell dans lesquelles la surface du plasma est initialement pré-structurée de sorte à satisfaire les conditions d'excitation de l'onde de surface. L'intensité laser a été variée entre Iλ2 =10^15 et 10^20 μm^2/Wcm^2 afin d'étudier la transition entre un régime d'excitation non-relativiste et relativiste. Les simulations dans lesquelles l'onde de surface est excitée sont comparées à celles où elle ne l'est pas et le couplage du laser avec la cible est analysé. Pour différents paramètres du laser et de la cible, nous avons considéré les quatre aspects suivants de l'interaction laser plasma : i) l'absorption laser et le champ électrique à la surface du plasma, ii) le champ magnétique quasi-statique généré, iii) le chauffage électronique et iiii) l'accélération des ions. Nous avons démontré la possibilité d'exciter une onde plasma de surface pour une large gamme d'intensité laser. Lorsque l'onde de surface est excitée, la composante perpendiculaire à la surface du plasma du champ électrique est amplifiée par rapport au champ laser sur la surface plasma-vide d'un facteur allant de 3. 2 à 7. 2 selon les cas. L'absorption augmente également fortement de 27% lorsque l'onde de surface n'est pas excitée à 73% lorsqu'elle l'est pour Iλ2=10^19 μm^2/Wcm^2 par exemple. Cette étude nous a permis de définir les conditions optimales pour lesquelles le couplage entre le laser et l'onde de surface est le plus efficace. Elles correspondent au régime d'intensité laser relativiste dans lequel le mécanisme d'absorption principale est le " vacuum heating " : les particules gagnent de l'énergie en oscillant dans le champ électrique perpendiculaire à la cible. En présence de l'onde de surface, cette oscillation est fortement augmentée par la présence du champ localisé de l'onde de surface plus intense que le celui du laser. La possibilité de créer des champs magnétiques quasi-statiques auto-générés en présence d'une onde de surface a de plus été étudiée analytiquement et les résultats ont été comparés à ceux des simulations. Les structures de champ obtenues suggèrent que l'intensité du champ magnétique généré induit un confinement partiel des particules sur la surface de la cible lorsque l'onde de surface est excitée. Enfin, nous avons observé un effet induit par l'excitation de l'onde de surface encore plus fort dans des cibles minces dans lesquelles les électrons peuvent circuler d'un bord à l'autre de la cible et interagir plusieurs fois avec le champ de l'onde. Le champ de charge d'espace ainsi créé au cours de l'interaction induit une augmentation importante de l'énergie des ions émis sur les deux faces de la cible mince. L'ensemble de ce travail nous a permis de montrer que l'excitation d'une onde de surface par interaction laser-plasma structuré est un mécanisme physique prometteur pour augmenter l'énergie des particules émises. C'est un point particulièrement intéressant pour les applications liées à la production de protons énergétiques telles que la thérapie hadronique ou à celle d'électrons de hautes énergies indispensables dans le processus de fusion inertiel dans lequel le schéma de l'allumeur rapide est utilisée
Surface waves in solids were first observed by Wood in 1902 as an anomaly in the diffraction of a continuous light source from a metal grating: the diffracted spectrum presented dark lines corresponding to certain wavelengths, which were later explained (Fano, 1941) in terms of the excitation of a surface wave sustained by the grating. Similarly to the metal grating case, a surface plasma wave (SPW) can be resonantly excited by a laser pulse at the surface of a laser-produced over-dense plasma, if the correct matching conditions are provided. SPWs propagate along the plasma-vacuum interface and are characterized by a localized, high frequency, resonant electric field. In the present work we describe numerically the dynamics of the plasma and the field distribution associated to SPW excitation, using two-dimensional particle-in-cell (PIC) simulations, where the plasma surface is initially pre-formed so that the SPW excitation conditions are fulfilled. We examine the surface wave excitation for a large range of laser intensities (Iλ2 =10^15-10^20 μm^2/Wcm^2) in order to study the transition from the non-relativistic to the relativistic regime. The simulations in which the wave is resonantly excited are compared to cases in which the resonant conditions are not provided and the coupling of the laser with the target is analyzed. We have considered the following aspects of the laser-plasma interaction, for different laser and target parameters: i) the laser absorption and the electric field at the surface ii) the generation of a quasi-static magnetic field iii) the electron heating and iiii) the ion acceleration. The possibility to excite a surface plasma wave on a structured target for a large range of laser energies has been demonstrated. In the cases where the surface wave is excited the electric field component normal to the target is amplified at the surface by a factor ranging from 3. 2 to 7. 2 with respect to the laser field. The absorption is also increased,for example it raises from 27% when the SPW is not excited up to 73% for Iλ^2=10^9 μm^2/Wcm^2. We have defined the optimal conditions for efficient coupling which increase laser absorption, that correspond to the relativistic laser intensities (Iλ^2>10^19 μm^2/Wcm^2). In this regime the main absorption mechanism is vacuum heating, associated to particles oscillating in the field perpendicular to the target, which is enhanced by the stronger, localized field of the SPW. The generation of a quasi-static magnetic field has been studied analytically and compared to the result of PIC simulations. The different field structure in presence of a SPW and for a flat target suggests that the enhanced field strength has caused partial confinement of particles at the target surface when SPW is present. The effects of the surface wave are more pronounced in thin laminar targets where electrons recirculate into the target interacting several times with the wave. Efficient electron heating increases the energy of the ions which are accelerated at both the irradiated and not irradiated target surface by the hot electrons space charge field. For the thinnest target (3. 5 μm) the ion cut-off energy is about 14 Mev, approximately twice the value obtained when the SPW is not excited

Étude du chauffage d'un plasma de tokamak par résonance à la fréquence cyclotronique électronique d'une onde de polarisation dite ordinaire. On s'intéresse d'une part aux modifications de températures qui apparaissent en raison de l'absorption par les électrons du plasma de la puissance transportée par l'onde et d'autre part, à l'évolution du transfert d'énergie au cours du chauffage

Para o aprimoramento do sistema de aquecimento do plasma por meio de ondas de Alfvén, denominado sistema AWES Alfvén Waves Excitment System, do tokamak TCABR foram construídos, caracterizados, instalados e colocados em operação os diagnósticos para determinação da potência de rádio-freqüência fornecida ao plasma pelo conjunto de antenas para excitação de ondas de Alfvén bem como o circuito processador de sinais para o conjunto de sondas magnéticas, já instaladas dentro da câmara do TCABR, que permitem determinar o espectro de rádio-freqüência gerado pelo conjunto de antenas no interior da câmara de vácuo deste tokamak. Cada conjunto do sistema de diagnóstico de potência é composto por três dispositivos, sendo eles, um sensor de corrente de rádio-freqüência, do tipo bobinas de Rogowski, um sensor de tensão de RF, composto de divisores de tensão acoplados a um circuito processador de sinais e por um circuito multiplicador de sinais capaz de multiplicar os sinais de corrente e tensão de RF e fornecer um sinal proporcional à potência efetivamente fornecida ao plasma. No total foram construídas dez bobinas de Rogowski cujas constantes de sensibilidade são da ordem de 18 mV/A, doze divisores de tensão capazes de reduzir a amplitude de um sinal de 10kV a aproximadamente 5V, seis circuitos processadores de sinais para determinação da tensão de RF e quatro multiplicadores de sinais. Além disso foi construído um circuito processador de sinais capaz de processar o sinal fornecido por quatro sondas magnéticas simultaneamente. Todos os dispositivos elaborados nesse trabalho são capazes de processar sinais de freqüências compreendidas na faixa de 3 a 6MHz e fornecer sinais de baixa freqüência tal que seja possível adquiri-los automaticamente pelo sistema de aquisição de dados do TCABR, denominado TCAqs. Para os procedimentos de calibração e testes de funcionamento dos equipamentos desenvolvidos neste trabalho, estabeleceu-se um Sistema de Calibração Automatizado (SCA) sendo uma de suas partes integrantes um software capaz de comunicar e controlar equipamentos de medição, tais como osciloscópios e geradores de sinais, através de portas de comunicação tipo RS-232 usando a linguagem de comunicação SCPI. Este programa, chamado de SCO, foi inteiramente desenvolvido em software livre e de código aberto para ser usado em sistemas operacionais Unix-Like, como os sistemas GNU/Linux. O código fonte do SCO foi liberado como software livre e com isso registrado sob a licença GNU/GPL. Os procedimentos de calibração uma vez operando sob esse sistema cuja principal característica é a funcionalidade de automação, permitiu a aquisição de uma quantidade de dados muito maior do que aquela que seria possível em procedimentos manuais, resultando assim, em curvas mais confiáveis do ponto de vista estatístico aumentando-se conseqüentemente, de forma considerável, a qualidade das medições. Após extensa caracterização e testes de funcionamento fora e no TCABR concluiu-se que estes dispositivos estão prontos para serem utilizados em campanhas experimentais.
In order to enhance the efficiency of the TCABR\'s Alfvén waves heating system, called AWES - Alfvén Waves Excitement System a diagnostics for determining the radio-frequency power applied to the plasma and a processing circuit for the magnetic coil system was built, characterized, installed and put into operation. The RF diagnostics system was designed to determine the total power that the set of AWES antennas applies to the plasma and, the magnetic coils system is designed to determine the RF spectrum excited by these antennas. Since the magnetic coils are already installed inside the TCABRs vacuum chamber only the signal processing circuit was built for it. The RF power diagnostics set is composed of three devices which are, one RF current sensing device, a set for determining the RF voltage and a multiplying system. A Rogowski coil is used for measuring the RF current. The RF voltage system may be split in two: a couple of voltage dividers and a processing circuit for the potential difference determination. Applying the RF current and voltage signals to the multiplier circuit it is possible to determine the RF power fed to the plasma. In this work a total of ten Rogowski coils, with 18mV/A sensibility constant, as well as twelve voltage dividers, capable of reducing a 10kV signal to approximately 5V signal, six voltage processing circuits and four signal multipliers, were built. Besides that, one demodulator circuit, capable of processing, simultaneously, the signals from four magnetic coils, was built too. All the devices constructed in this project were designed to be able to process signals with frequencies in the range of 3 to 6M Hz and produce a low frequency result signal that may be acquired automatically by the TCABR data acquisition system called TCAqs. For the calibration procedures and operational tests of the equipments developed in this work, it was established an Automated Calibration System (SCA) with a software application as one of its components that is capable of communicating and controlling test instruments, like oscilloscopes and function generators, through the communication port RS-232 and SCPI language. This software, called SCO, was fully developed using free and open source software in order to be used in Unix-Like operational systems like GNU/Linux. As a free software SCO was registered under the GNU/GPL license. The calibration procedures once operating with this system, whose principal characteristics is its automation functionality, allowed us to acquire a great quantity of data, that would have not been possible or practical to do manually. As a consequence, the resulting calibration curves may be considered more accurate, from an statistical point of view which enhanced considerably the quality of the results. After the characterization and detailed tests of all these devices off the TCABR and after the installation of the diagnostics in the TCABR, we may finally conclude they are ready to be used in experimental campaign.

L'objet de la thèse est le développement d'un modèle numérique bidimensionnel de simulation du chauffage d'un bain métallique anodique par un plasma d'arc transféré. La configuration retenue est proche de celle du four à arc transféré de petite capacité (200kw - 2000a, 40 litres) développé au laboratoire plasma d'EDF-der aux renardières pour étudier les transferts thermiques dans ce type de chauffage. Le modèle permet le calcul des différents champs (vitesse, température, turbulence, électromagnétique) dans la région de l'arc électrique, dans le bain et dans l'électrode de sole. Les équations de Navier-Stokes couplées aux équations de l'électromagnétisme sont résolues dans chaque domaine par une méthode numérique aux différences finies ou volumes finis à pas fractionnaires. Pour le calcul de l'arc, les transferts radiatifs sont également calcules ainsi que le transport des vapeurs métalliques et leurs effets sur les propriétés du plasma. Un modèle monodimensionnel spécifique est utilise pour la modélisation de la couche limite anodique au-dessus du bain. Le couplage du calcul arc avec le calcul du bain est assure par des conditions aux limites a l'interface. Deux cas de longueur d'arc, 0,15m et 0,25m, ont été traites. Les résultats seront présentés et comparés avec des mesures de flux effectuées sur le four dans des conditions similaires.

The neutron spectrometer TOFOR was installed at JET in 2005 for high-rate observation of neutrons from reactions between two deuterium (D) ions. Neutron spectrometry as a fusion plasma diagnostic technique is invoked to obtain information about the velocity states of fusion fuel ions. Based on neutron spectrometry data, conclusions can be drawn on the efficiency of plasma heating schemes as well as optimization of fuel ion confinement. The quality of TOFOR analysis is found to depend on how well the instrument response function is known; discriminator threshold levels, detector time alignment and electronics broadening are identified as crucial issues. About 19 percent of the neutrons observed with TOFOR have scattered off the JET vessel wall or other structures in the line-of-sight before reaching the instrument, as established through simulations and measurements. A method has been developed to take these neutrons into account in the analysis. TOFOR measurements of fast deuterium distributions are seen to agree with distributions deduced from NPA data, obtained based on an entirely different principle. This serves as validation of the modeling and analysis. Extraordinary statistics in the TOFOR measurements from JET pulses heated with 3rd harmonic RF heating on D beams allow for study of instabilities using neutron emission spectrometry. At ITER, similar studies should be possible on a more regular basis due to higher neutron rates. Observations of neutrons from Be+3He reactions in the TOFOR spectrum from D plasmas heated with fundamental RF tuned to minority 3He raise the question of beryllium neutrons at JET after installation of the ITER-like wall, and at ITER, with beryllium as the plasma facing component. This is especially important for the first few years of ITER operation, where the machine will not yet have been certified as a nuclear facility and should be run in zero-activation mode.

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The processing of materials through plasma has been growing enough in the last times in several technological applications, more specifically in surfaces treatment. That growth is due, mainly, to the great applicability of plasmas as energy source, where it assumes behavior thermal, chemical and/or physical. On the other hand, the multiplicity of simultaneous physical effects (thermal, chemical and physical interactions) present in plasmas increases the complexity for understanding their interaction with solids. In that sense, as an initial step for the development of that subject, the present work treats of the computational simulation of the heating and cooling processes of steel and copper samples immersed in a plasma atmosphere, by considering two experimental geometric configurations: hollow and plane cathode. In order to reach such goal, three computational models were developed in Fortran 90 language: an one-dimensional transient model (1D, t), a two-dimensional transient model (2D, t) and a two-dimensional transient model (2D, t) which take into account the presence of a sample holder in the experimental assembly. The models were developed based on the finite volume method and, for the two-dimensional configurations, the effect of hollow cathode on the sample was considered as a lateral external heat source. The main results obtained with the three computational models, as temperature distribution and thermal gradients in the samples and in the holder, were compared with those developed by the Laboratory of Plasma, LabPlasma/UFRN, and with experiments available in the literature. The behavior showed indicates the validity of the developed codes and illustrate the need of the use of such computational tool in that process type, due to the great easiness of obtaining thermal information of interest
O processamento de materiais por plasmas tem crescido bastante nos ?ltimos tempos em diversas aplica??es tecnol?gicas, mais especificamente no tratamento de superf?cies. Esse crescimento se deve, principalmente, pela grande aplicabilidade do plasma como fonte energ?tica. Por outro lado, a multiplicidade de efeitos simult?neos presentes no plasma, (intera??es t?rmicas, qu?micas e f?sicas) aumenta a complexidade para entendimento da sua intera??o com s?lidos. Nesse sentido, como um passo inicial para o desenvolvimento desse tema, o presente trabalho trata da simula??o computacional de aquecimento e resfriamento de amostras de a?o e cobre em ambientes de plasma, considerando-se duas configura??es geom?tricas: catodo oco e catodo planar. Para tal, tr?s modelos computacionais foram desenvolvidos na linguagem Fortran 90: um modelo unidimensional transiente sem suporte (1D,t), um modelo bidimensional transiente sem suporte (2D,t) e um modelo bidimensional transiente (2D,t) que considera a presen?a de um suporte na montagem experimental. Os modelos foram desenvolvidos utilizando-se o m?todo dos volumes finitos e, para as situa??es bidimensionais, o efeito de catodo oco sobre a amostra foi considerado como uma fonte externa de calor lateral. Os resultados obtidos com os tr?s modelos computacionais, como a distribui??o de temperatura nas amostras e nos suportes, os seus gradientes t?rmicos, em fun??o de alguns experimentos de aquecimento e resfriamento desenvolvidos pelo Laborat?rio de Plasma, LabPlasma/UFRN, e de experimentos reportados na literatura, apontam para a validade dos c?digos desenvolvidos e ilustram a necessidade da utiliza??o dessa ferramenta nesse tipo de processo, pela sua facilidade de disponibiliza??o de informa??es t?rmicas de interesse

Thesis (Ph.D.)--Mechanical Engineering, Georgia Institute of Technology, 2008.
Committee Co-Chair: Minami Yoda, Co-Advisor; Committee Co-Chair: Said I. Abdel-Khalik; Committee Member: Donald R. Webster; Committee Member: Narayanan M. Komerath; Committee Member: S. Mostafa Ghiaasiaan; Committee Member: Yogendra Joshi