Neste trabalho o formalismo semi-clássico convergente sugerido por Cattani é desenvolvido para calcular o alargamento e deslocamento provocado por colisões eletrônicas de linhas espectrais de átomos neutros em plasmas . Para testar o referido formalismo calculamos a largura e o deslocamento de muitas linhas espectrais do hélio neutro em plasmas com temperaturas que vão desde 5000 até 40000K e densidades eletrônicas que variam de 10 POT. -15 até 10 POT. -18cm POT. -3. Efeitos de \"screening\" de Debye e trajetória não retilínea dos elétrons são levados em conta no formalismo. Um estudo sobre a contribuição das colisões iônicas para o alargamento e deslocamento desenvolvido para elétrons e as aproximações quase estática de Griem e adiabática de Barnard, Cooper e Smith, e Griem, Baranger, Kolb e Oertel. Os alargamentos e deslocamentos calculados são comparados com resultados experimentais obtidos por Wulff, Berg e colaboradores, Kelleher e Diatta e teóricos previstos por Griem e Sahal-Bréchot. / n this work the semiclassical convergent formalism suggested by Cattani is developed to calculate the broadening and shift of spectral lines produced by electronic collisions of neutral atoms in plasmas. To test this theory we calculate the widths and shifts of many spectral lines of neutral helium in plasmas with temperatures that goes from 5000 up to 40000 K and electronic densities in the range of 10 POT. -15 até 10 POT. -18cm POT. -3. Effects of Debye screening and non straight line trajectory are taken into account in our approach. To study the ionic collisional contribution to the widths and shifts we use the same convergent treatment developed for electrons and the quasi-static approximation of Griem and adiabatic approximation of Barnard, Cooper and Smith, and Griem, Baranger, Kolb and Oertel. The calculated widths and shifts are compared with experimental results obtained by Wulff, Berg and collaborators, Kelleher and Diatta and theoretical predictions of Griem and Sahal-Bréchot.

Thermonuclear fusion has potential to offer an economically, environmentally and socially acceptable supply of energy. A promising reactor design to execute thermonuclear fusion is the toroidal magnetic confinement device, tokamak. The tokamak still faces challenges in the major areas which can be categorised into confinement, heating and fusion technology. This thesis addresses the problem of confinement, in particular the role of transport along magnetic field lines perturbed by diverse MHD instabilities. Unstable modes such as ideal ballooning-peeling, tearing etc., break closed magnetic surfaces and destroy the axisymmetry of the magnetic configuration in a tokamak, providing deviation of magnetic field lines from unperturbed magnetic surfaces. Radial gradients of plasma parameters have nonzero projections along such lines and drive parallel particle and heat flows which contribute to the radial transport. Such transport can significantly affect confinement as this takes place by the development of neoclassical tearing modes (NTMs) in the core and edge localised modes (ELMs) at the plasma periphery. In this thesis, transport of heat through non-overlapped magnetic island chains is first investigated using the 'Optimal path' approach, which is based on the principal of minimum entropy production. This model shows how the effective heat conduction through islands increases with parallel heat conduction and with the perturbation level. A more standard analytical approach for the limit cases of "small" and "large" islands is also presented. Transport of heat through internally heated magnetic islands is next investigated by further development of the 'Optimal path' method. In addition the approach by R. Fitzpatrick, has been extended for this investigation. By application of these approaches to experimental observations made at TEXTOR tokamak, heat flux limit, limiting parallel heat conduction in low collisional plasmas, is elucidated. Models to study transport of heat and particles due to ELMs have also been developed. Energy losses during ELMs have been estimated considering contribution from parallel conduction due to electrons and parallel convection of ions, with constant level of the magnetic field perturbation, steady profiles for density and temperature, and by accounting for the heat flux limit. The estimate shows good agreement with experimental observations. The model is developed further by accounting for the time evolution of the perturbation level due to ballooning mode, and of density and temperature profiles.

Cellular behaviour depends ultimately on the transcription of genes. If we know how transcription is controlled we have a better chance of understanding cellular processes. This thesis presents six studies, all concerning cellular regulatory mechanisms. One study is purely experimental and five are computational studies. A large part of the research concerns the Epstein-Barr virus (EBV). We investigate the latency programme switching of EBV, with an equilibrium statistical mechanics model that describes the transcription activities of two central viral promoters. We demonstrate that this system is bistable and predict promoter activities that correlate well with experimental data. Further we study the switching efficiency of one of the promoters, highlighting how competitive binding of transcription factors generates a more efficient geneticswitch. The EBV protein EBNA1 is known to affect cellular gene expression. With a dinucleotide position weight matrix we search the complete human genome for regions with multiple EBNA1 binding sites. 40 potential binding regions are identified, with several of particular interest in relation to EBV infections. The final study on EBV is purely experimental, in which we demonstrate an interaction between the Syk kinase and integrin β4. Moreover, we show how reduced levels of these proteins affect migration of epithelial LMP2a positive cells, and hypothesise that these effects are due to the Syk-β4 interaction. The two remaining studies presented in this thesis concern other cellular systems. Dynamic properties of two different regulatory feedback mechanisms for transport and metabolism of small molecules are investigated. The synergetic effect of adding a regulatory loop is exemplified with the iron metabolism in bacteria. The final project concerns the λ phage. With the equilibrium statistical mechanics method for describing promoter activities we characterise the equilibrium properties of λ mutants and compare with experimental findings. We argue that the observed differences between model and experiment are due to a larger perturbation of the genetic circuit than presumed. The research presented in this thesis shed light on the properties of several regulatory mechanisms. As computational studies they add perspective to the experimental research in this field and provide new hypothesis for further research. / QC20100720

<p> We report the observation of a net inward, up-gradient turbulent particle flux which occurs when a collisional drift waves generate a sufficiently strong radially sheared azimuthal zonal flow in a cylindrical magnetized plasma. At low magnetic fields (B&le;1.0 kG), particle transport is outward at all radii. As the magnetic field is further increased to 1200G, an up-gradient inward particle flux develops between the peak of the velocity shear and the maximum density gradient. The mean density gradient is also observed to steepen in response to this inward flux. Time-domain and bispectral Fourier domain analysis shows that at the peak of the velocity shear, where the particle flux is outward, the turbulent Reynolds stress acts to reinforce the shear flow. In contrast, in the region of the inward particle flux, the zonal flow drives the fluctuations, and a transient increase in the shearing rate is occurs prior to an increase in the magnitude of the inward flux. The results suggest a hypothesis in which the shear flow is responsible for the up-gradient particle flux and the corresponding steepening in the mean density gradient. However, a linear instability analyses using experimentally measured density and E&times;B flow profiles in a linear, modified Hasegawa-Wakatani theory model with the coupled potential and density fluctuations failed to reproduce the essential elements of our experimental observations, suggesting some other mechanism is responsible for the inward flux. We summarize recent new experimental results which point towards the possible role of finite ion temperature gradient effects, possibly combined with parallel flow shear, in driving up-gradient particle flux.</p>

Kinetic microinstabilities in the solar wind arise when its non-thermal properties become too extreme. This thesis project focused specifically on the four instabilities associated with ion temperature anisotropy: the cyclotron, mirror, and parallel and oblique firehose instabilities. Numerous studies have provided evidence that proton temperature anisotropy in the solar wind is limited by the actions of these instabilities. For this project, a fully revised analysis of data from the Wind spacecraft's Faraday cups and calculations from linear Vlasov theory were used to extend these findings in two respects. First, theoretical thresholds were derived for the \(\alpha\)-particle temperature anisotropy instabilities, which were then found to be consistent with a statistical analysis of Wind \(\alpha\)-particle data. This suggests that \(\alpha\)-particles, which constitute only about 5% of ions in the solar wind, are nevertheless able to drive temperature anisotropy instabilities. Second, a statistical analysis of Wind proton data found that proton temperature was significantly enhanced in plasma unstable due to proton temperature anisotropy. This implies that extreme proton temperature anisotropies in solar wind at 1 AU arise from ongoing anisotropic heating (versus cooling from, e.g., CGL double adiabatic expansion). Together, these results provide further insight into the complex evolution of the solar wind's non-fluid properties. / Astronomy

The report contained herein is a statistical analysis of electron temperatures withinTitan’s lower ionosphere. Electron temperatures in this altitudinal range are of greatimport for researchers. The main contributing factors are investigated to see whatphysical processes are the sources of variability in electron temperatures. Oneimportant result from this analysis lends itself to determining recombinationcoefficients thus determining organic process rates occurring within Titan’satmosphere. To accomplish this analysis, data from the Langmuir probe aboard the Cassini craft isutilized. The Langmuir probe is an instrument which can be used to measure currentdifferences in a plasma environment. From this, plasma properties such astemperature, density, and velocity can be calculated. It was named after IrvingLangmuir, whose theories became the basis for Orbit Motion Limited theory. Of the possible factors that determine the variation in electron temperatures, altitudewas the most evident and largest contributor. Once the data had been reduced toremove the effect of altitude on the temperature, other factors such as latitude, solarzenith angle, and ram angle were investigated to ascertain which, if any, wasresponsible for variations in temperature. Upon completion of the analysis, it waslearned that ram angle also had an identifiable effect upon electron temperatures. This effect was further investigated to ensure confidence in the results. Thecompletion of this part of the analysis showed that the effect shown with respect toram angle was indeed reproducible and that no other investigated factor had a majoreffect on electron temperatures. After the confidence procedure was completed,several previous studies findings were confirmed. These confirmed results include therelation of solar zenith angle with respect to both electron temperature distributionand density distribution, as well as a possible confirmation relating temperature anddensity for electrons.n/

<p> Tokamaks use magnetic fields to confine plasmas to achieve fusion; they are the leading approach proposed for the widespread production of fusion energy. The sawtooth crash in tokamaks limits the core temperature, adversely impacts confinement, and seeds disruptions. Adequate knowledge of the physics governing the sawtooth crash and a predictive capability of its ramifications has been elusive, including an understanding of incomplete reconnection, i.e., why sawteeth often cease prematurely before processing all available magnetic flux. In this dissertation, we introduce a model for incomplete reconnection in sawtooth crashes resulting from increasing diamagnetic effects in the nonlinear phase of magnetic reconnection. Physically, the reconnection inflow self-consistently convects the high pressure core of a tokamak toward the <i>q</i>=1 rational surface, thereby increasing the pressure gradient at the reconnection site. If the pressure gradient at the rational surface becomes large enough due to the self-consistent evolution, incomplete reconnection will occur due to diamagnetic effects becoming large enough to suppress reconnection. Predictions of this model are borne out in large-scale proof-of-principle two-fluid simulations of reconnection in a 2D slab geometry and are also consistent with data from the Mega Ampere Spherical Tokamak (MAST). Additionally, we present simulations from the 3D extended-MHD code M3D-C¹ used to study the sawtooth crash in a 3D toroidal geometry for resistive-MHD and two-fluid models. This is the first study in a 3D tokamak geometry to show that the inclusion of two-fluid physics in the model equations is essential for recovering timescales more closely in line with experimental results compared to resistive-MHD and contrast the dynamics in the two models. We use a novel approach to sample the data in the plane of reconnection perpendicular to the <i>(m,n)</i>=(1,1) mode to carefully assess the reconnection physics. Using local measures of reconnection, we find that it is much faster in the two-fluid simulations, consistent with expectations based on global measures. By sampling data in the reconnection plane, we present the first observation of the quadrupole out-of-plane magnetic field appearing during sawtooth reconnection with the Hall term. We also explore how reconnection as viewed in the reconnection plane varies toroidally, which affects the symmetry of the reconnection geometry and the local diamagnetic effects. We expect our results to be useful for transport modeling in tokamaks, predicting energetic alpha-particle confinement, and assessing how sawteeth trigger disruptions. Since the model only depends on local diamagnetic and reconnection physics, it is machine independent, and should apply both to existing tokamaks and future ones such as ITER.</p>

<p> Magnetic fields at all scales are prevalent in our universe. However, current cosmological models predict that initially the universe was bereft of large-scale fields. Standard magnetohydrodynamics (MHD) does not permit magnetogenesis; in the MHD Faraday&rsquo;s law, the change in magnetic field <i> B</i> depends on <i>B</i> itself. Thus if <i> B</i> is initially zero, it will remain zero for all time. A more accurate physical model is needed to explain the origins of the galactic-scale magnetic fields observed today. In this thesis, I explore two velocity-driven mechanisms for magnetogenesis in 2-fluid plasma. The first is a novel kinematic &lsquo;battery&rsquo; arising from convection of vorticity. A coupling between thermal and plasma oscillations, this non-relativistic mechanism can operate in flows that are incompressible, quasi-neutral and barotropic. The second mechanism results from inclusion of thermal effects in relativistic shear flow instabilities. In such flows, parallel perturbations are ubiquitously unstable at small scales, with growth rates of order with the plasma frequency over a defined range of parameter-space. Of these two processes, instabilities seem far more likely to account for galactic magnetic fields. Stable kinematic effects will, at best, be comparable to an ideal Biermann battery, which is suspected to be orders of magnitude too weak to produce the observed galactic fields. On the other hand, instabilities grow until saturation is reached, a topic that has yet to be explored in detail on cosmological scales. In addition to investigating these magnetogenesis sources, I derive a general dispersion relation for three dimensional, warm, two species plasma with discontinuous shear flow. The mathematics of relativistic plasma, sheared-flow instability and the Biermann battery are also discussed.</p>

The motion of a theta pinch hydrogen plasma in the presence of a local perturbing magnetic field is described. A small coil outside the plasma was excited by capacitors to produce a dipole field. Experiments were performed on a 3.5m long, collisional, high-beta plasma with a temperature of 60 eV, a radius of 1 cm and a density of 10¹⁶ particles cm^-3. Sinusoidal currents of 20kA and frequency 10⁶ rad s^-1 in a 3-turn perturbing field coil produced oscillating plasma displacements of 1 cm, which propagated along the plasma with a velocity of 20 cm mus^-1. The displacement was proportional to the coil current, inversely proportional to the axial magnetic field outside the plasma, and was spatiplly damped with an e-folding length of 20 cm. Using a step current waveform the plasma could be moved to an equilibrium position which was displaced from the initial unperturbed equilibrium. Experiments on a 2 m long low-beta plasma with a temperature of 10 eV showed that propagating plasma displacements of 0.5 cm could be obtained, which were damped in 5 cm. Predictions of the plasma displacement and velocity are made by considering the motion as long wavelength, m = 1 perturbations about an equilibrium position. Damping mechanisms are introduced by making an analogy between the excited waves and Alfven waves in a dissipative medium. Feedback stabilization of long wavelength gross modes in theta-pinch plasmas is shown to be possible, using a system of coils similar to those used to excite plasma motion. Experiments were performed to determine the effect of the initial conditions on the 3.5m theta-pinch parameters, and the results compared with computations. A computed heating rate was obtained; including partial ionization of the initial gas revealed a value of the initial rate of change of axial magnetic field below which no heating occurred. This cut-off was overcome experimentally by using bias fields.

The azimuthal magnetic field and current density structure of a Plasma Focus device, have been investigated by the observation of the Faraday rotation of a ruby laser probe beam. The magnetic field and current distributions play important roles in plasma compression, heating, confinement, stability, and particle acceleration. However, in over two decades of research, no satisfactory experimental data on the field or the current have been produced. The results reported are of the first measurements of magnetic field and current distribution in the Plasma Focus, using a non perturbing diagnostic technique. A full description of the experimental apparatus and method, the physics of the differential polarimetry (with refraction effects included), and theoretical reviews of Faraday rotation, birefringence, dichroism, and refraction, are given. It was found that during the collapse phase of the discharge, times t = -10 ns to t = 0 ns (peak compression), the current and field are confined to the plasma skin. The penetration depth is 0.56 mm, and the resistivity is classical. During the dense pinch phase, between t = 0 ns and t = +10 ns, the plasma develops a turbulent core, of radius 2 mm, in which the resistivity is highly anomalous (by a factor 6000). This results in a rapid diffusion (lasting approximately 10 ns) of field and current (typically 20 of the total) into the core. Particle acceleration is suppressed at this stage because the ion Hall term is less than unity. Outside this core, the resistivity is classical, and the current is carried in the plasma skin. At times t = +10 ns to t = +15 ns, axial current filamentation was observed. These filaments last less than 2.5 ns, and carry in excess of 12% of the current. Future studies of the filamentation should lead to a better understanding of the intense neutron production observed in Plasma Focus devices.