To understand the physical mechanism underlying the cross-field transport of mass and energy in magnetoplasmas is a long-standing problem in fusion research. Woods (1987) has recently developed a second-order transport theory which has been used to explain a number of transport-related phenomena observed in tokamaks. Here, we apply second-order transport theory to the reverse field pinch (RFP) and a phenomenon observed in tokamaks known as 'snakes'. Expressions for the mass and energy confinement times in the RFP, τ_p and τ_e, are deduced and agreement with experimental results from HBTX is found. For typical operating conditions the times τ_p ~ 0.1ms and τ_e ~ 0.2ms are observed in HBTX. Second-order transport theory predicts τ_p ~ 0.4ms and τ_e ~ 0.4ms for this machine. Scaling laws for β_p versus η_e,β_p versus I_φ and τ_e versus I_φ are compared with measurements from HBTX and agree well with observation. Snakes are large density perturbations observed in JET after fuel pellet injection. Typical snakes in JET are remarkably stable and are found to have density decay times longer than predictions based on neoclassical theory (Stringer 1987). After their formation, snakes have even been observed to grow (Weller <i>et al.</i> 1987), which suggests the presence of an inward diffusion mechanism. There is also some evidence for a temperature depression in the snakes region. An explanation of the stability and energy balance in snakes based on second-order transport theory is proposed.

The need to make maximum use of renewable resources to the detriment of fossil fuels to achieve environmental goals with an increasing energy demand is driving research into the development of technologies to obtain energy from sources that are not currently being exploited, one of them being fusion energy. The aim of this report is to provide a general overview of fusion and to provide a critical opinion on whether fusion will become a commercial energy source in the future, and if so when. The followed methodology has been a literature review complemented by an interview to B Henric M Bergsåker, teacher and researcher at the KTH on fusion plasma physics and information person for the Swedish fusion research.In the results section the fusion physics and different technological approaches have been presented. Among the studied different projects, the ITER Tokamak magnetic reactor has been selected as the most promising of these projects, as a product of international collaboration, and it has been analyzed in more detail. The obtained results have been that fusion can be an inexhaustible, environmentally friendly and safe energy source. The first-generation fusion commercial reactors are expected to be part of the energy mix before 2100.

Desenvolvemos uma aplicação das análises espectrais por Fourier e wavelet para o estudo de flutuações intermitentes e não estacionárias. Para isso, elaboramos algoritmos adequados, que revelam os modos principais presentes nas flutuações analisadas e as suas evoluções. Baseados nesses algoritmos, apresentamos um método para a seleção de \"bursts\" (irrupções) em meio ao background da série intermitente anali­sada. Inicialmente, aplicamos essa análise às flutuações intermitentes obtidas inte­grando numericamente as equações de Lorenz. Dessa forma, obtivemos a evolução do espectro das frequências dessas flutuações e selecionamos os seus bursts. Simi­larmente, obtivemos a evolução dos espectros de frequência de flutuações elétricas turbulentas medidas no tokamak TCABR. Confirmamos que a análise por wavelet é adequada para observar a modulação da turbulência pelas oscilações magnéticas. Para essas flutuações, selecionamos os bursts intermitentes presentes nas flutuações turbulentas e obtivemos as distribuições dos intervalos de tempo entre bursts sucessivos. Obtivemos, ainda, as distribuições das medidas da flutuação da turbulência no TCABR. Com a modulação mencionada, a distribuição obtida pode ser reproduzida como a convolução entre as distribuições senoidais (associadas às flutuações magnéticas) e uma distribuição (associada às flutuações turbulentas) como a obser­vada sem a modulação (como as observadas no plasma não perturbado). / We apply the Fourier and wavelet spectral analyses to study nonstationary inter­mittent fluctuations. For that we introduce algorithms that show the dominant fre­quency modes and their evolution. Moreover, applying these algorithms, we present a method to discriminate the burst from the background in the intermittent fluctuations. Initially, we apply this analysis to the intermittent fluctuations obtained integrating numerically the Lorenz equations. Thus, we obtain the frequency spectra evolution of these fluctuations as well as the selected bursts sequence. Similarly, we obtain the frequency spectra evolution for the electric plasma edge turbulence in the TCABR tokamak. We confirm that the wavelet analysis describes well the turbulence modulation by the magnetic fluctuations. For this turbulence, we selected the intermittent bursts and present the histograms of the time interval between two successive bursts. Furthermore, we also present the PDFs of the total turbulent fluctuations. When the turbulence is modulated by the magnetic fluctuation, the observed PDF is interpreted as the convolution between sine distributions (due to the magnetic fluctuations influence) and the distribution (due to the turbulence) observed without modulation.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering; and, (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1978. / Includes bibliographical references. / by Abolghaasem Fadaai. / Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering; and, (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1978.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Robert Edward Potok. / Sc.D.

Z-Pinch IFE (Inertial Fusion Energy) reactor designs will likely utilize high yield targets (~ 3 GJ) at low repetition rates (~ 0.1 Hz). Appropriately arranged thick liquid jets can protect the cavity walls from the target x-rays, ions, and neutrons. However, the shock waves and mechanical loadings produced by rapid heating and evaporation of incompressible liquid jets may be challenging to accommodate within a small reactor cavity. This investigation examines the possibility of using two-phase compressible (liquid/gas) jets to protect the cavity walls in high yield IFE systems, thereby mitigating the mechanical consequences of rapid energy deposition within the jets. Two-phase, free, vertical jets with different cross sections (planar, circular, and annular) were examined over wide ranges of liquid velocities and void fractions. The void fraction and bubble size distributions within the jets were measured; correlations to predict variations of the slip ratio and the Sauter mean diameter were developed. An exploding wire system was used to generate a shock wave at the center of the annular jets. Attenuation of the shock by the surrounding single- or two-phase medium was measured. The results show that stable coherent jets can be established and steadily maintained over a wide range of inlet void fractions and liquid velocities, and that significant attenuation in shock strength can be attained with relatively modest void fractions (~ 1%); the compressible two-phase jets effectively convert and dissipate mechanical energy into thermal energy within the gas bubbles. The experimental characteristics of single- and two-phase jets were compared against predictions of a state-of-art CFD code (FLUENT®). The data obtained in this investigation will allow reactor system designers to predict the behavior of single- and two-phase jets and quantify their effectiveness in mitigating the consequences of shock waves on the cavity walls in high yield IFE systems.

Experimental and numerical studies simulating the gas-cooled divertor plate design concept have been carried out. While thermo-fluid and thermo-mechanical analyses have been previously performed to show the feasibility of the divertor plate design and its ability to accommodate a maximum heat flux of up to 10 MW/m2, no experimental data have heretofore been published to support or validate such analyses. To that end, this investigation has been undertaken. A test module with prototypical cross-sectional geometry has been designed, constructed, and instrumented. Experiments spanning the prototypical Reynolds numbers of the helium-cooled divertor have been conducted using pressurized air as the coolant. A second test module where the planar jet exiting the inlet manifold is replaced by a two-dimensional hexagonal array of circular jets over the entire top surface of the inlet manifold has also been tested. The thermal performance of both test modules with and without a porous metallic foam layer in the gap between the outer surface of the inlet manifold and the cooled surfaces of the pressure boundary were directly compared. For a given mass flow rate, the slot design with the metallic foam insert showed the highest heat transfer coefficient, with a pressure drop lower than that of the array of circular jets without foam. Additionally, numerical simulations matching the experimental operating conditions for the two cases without foam were performed using the computational fluid dynamics software package, FLUENT® v6.2. Comparisons of the experimental and numerical pressure drop, temperature, and heat transfer coefficient were made.

The common observation that the onset of a core MARFE (edge localized, poloidally asymmetric, highly radiating region) is followed immediately by a High-to-Low confinement mode transition in DIII-D was investigated by comparing a theoretical prediction of the threshold non-radiative power across the separatrix needed to maintain H-mode with an experimental determination of the non-radiative power flowing across the separatrix. It was found that in three shots with continuous gas fueling that the increased neutral influx associated with the MARFE formation caused a sharp increase in the predicted threshold non-radiative power crossing the separatrix that was required for the plasma to remain in H-mode to a value comparable to the experimental power crossing the separatrix, indicating a theoretical prediction of a H-L transition in agreement with experimental observation.

An experimental and numerical investigation has been conducted to examine steady, internal, nozzle-generated, gas/liquid mist cooling in vertical channels with ultra-thin, evaporating subcooled liquid films. Interest in this research has been motivated by the need for a highly efficient cooling mechanism in high-power lasers for inertial fusion reactor applications. The aim is to quantify the effects of various operating and design parameters, viz. liquid atomization nozzle design (i.e. spray geometry, droplet size distribution, etc.), heat flux, liquid mass fraction, film thickness, carrier gas velocity, temperature, and humidity, injected liquid temperature, gas/liquid combinations, channel geometry, length, and wettability, and flow direction, on mist cooling effectiveness. A fully-instrumented experimental test facility has been designed and constructed. The facility includes three cylindrical and two rectangular electrically-heated test sections with different unheated entry lengths. Water is used as the mist liquid with air, or helium, as the carrier gas. Three types of mist generating nozzles with significantly different spray characteristics are used. Numerous experiments have been conducted; local heat transfer coefficients along the channels are obtained for a wide range of operating conditions. The data indicate that mist cooling can increase the heat transfer coefficient by more than an order of magnitude compared to forced convection using only the carrier gas. The data obtained in this investigation will allow designers of mist-cooled high heat flux engineering systems to predict their performance over a wide range of design and operating parameters. Comparison has been made between the data and predictions of a modified version of the KIVA-3V code, a mechanistic, three-dimensional computer program for internal, transient, dispersed two-phase flow applications. Good agreement has been obtained for downward mist flow at moderate heat fluxes; at high heat fluxes, the code underpredicts the local heat transfer coefficients and does not predict the onset of film rupture. For upward mist flow, the code underpredicts the local heat transfer coefficients and, contrary to experimental observations, predicts early dryout at the test section exit.

Includes Van Allen thesis (M.S.)--University of Iowa, 1936, and thesis (Ph.D.)--University of Iowa, 1939.