http://hdl.handle.net/1721.1/7854 Sat, 08 Jun 2013 13:59:39 GMT 2013-06-08T13:59:39Z http://hdl.handle.net/1721.1/79031 Generation of acoustic-gravity waves in ionospheric HF heating experiments : simulating large-scale natural heat sources Pradipta, Rezy In this thesis, we investigate the potential role played by large-scale anomalous heat sources (e.g. prolonged heat wave events) in generating acoustic-gravity waves (AGWs) that might trigger widespread plasma turbulence in the ionospheric layer. The main hypothesis is that, the thermal gradients associated with the heat wave fronts could act as a source of powerful AGW capable of triggering ionospheric plasma turbulence over extensive areas. In our investigations, first we are going to examine a case study of the summer 2006 North American heat wave event. Our examination of GPS-derived total electron content (TEC) data over the North American sector reveals a quite noticeable increase in the level of daily plasma density fluctuations during the summer 2006 heat wave period. Comparison with the summer 2005 and summer 2007 data further confirms that the observed increase of traveling ionospheric disturbances (TIDs) during the summer 2006 heat wave period was not simply a regular seasonal phenomenon. Furthermore, a series of field experiments had been carried out at the High-frequency Active Auroral Research Program (HAARP) facility in order to physically simulate the process of AGW/TID generation by large-scale thermal gradients in the ionosphere. In these ionospheric HF heating experiments, we create some time-varying artificial thermal gradients at an altitude of 200-300 km above the Earth's surface using vertically-transmitted amplitude-modulated 0-mode HF heater waves. For our experiments, a number of radio diagnostic instruments had been utilized to detect the characteristic signatures of heater-generated AGW/TID. So far, we have been able to obtain several affirmative indications that some artificial AGW/TID are indeed being radiated out from the heated plasma volume during the HAARP-AGW experiments. Based on the experimental evidence, we may conclude that it is certainly quite plausible for large-scale thermal gradients associated with severe heat wave events to generate some AGW which might induce widespread plasma turbulence far in space. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 203-208). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/79031 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/79025 Sensitivity analysis and optimization of the nuclear fuel cycle : a systematic approach Passerini, Stefano For decades, nuclear energy development was based on the expectation that recycling of the fissionable materials in the used fuel from today's light water reactors into advanced (fast) reactors would be implemented as soon as technically feasible in order to extend the nuclear fuel resources. More recently, arguments have been made for deployment of fast reactors in order to reduce the amount of higher actinides, hence the longevity of radioactivity, in the materials destined to a geologic repository. The cost of the fast reactors, together with concerns about the proliferation of the technology of extraction of plutonium from used LWR fuel as well as the large investments in construction of reprocessing facilities have been the basis for arguments to defer the introduction of recycling technologies in many countries including the US. In this thesis, the impacts of alternative reactor technologies on the fuel cycle are assessed. Additionally, metrics to characterize the fuel cycles and systematic approaches to using them to optimize the fuel cycle are presented. The fuel cycle options of the 2010 MIT fuel cycle study are re-examined in light of the expected slower rate of growth in nuclear energy today, using the CAFCA (Code for Advanced Fuel Cycle Analysis). The Once Through Cycle (OTC) is considered as the base-line case, while advanced technologies with fuel recycling characterize the alternative fuel cycle options available in the future. The options include limited recycling in LWRs and full recycling in fast reactors and in high conversion LWRs. Fast reactor technologies studied include both oxide and metal fueled reactors. Additional fuel cycle scenarios presented for the first time in this work assume the deployment of innovative recycling reactor technologies such as the Reduced Moderation Boiling Water Reactors and Uranium-235 initiated Fast Reactors. A sensitivity study focused on system and technology parameters of interest has been conducted to test the robustness of the conclusions presented in the MIT Fuel Cycle Study. These conclusions are found to still hold, even when considering alternative technologies and different sets of simulation assumptions. Additionally, a first of a kind optimization scheme for the nuclear fuel cycle analysis is proposed and the applications of such an optimization are discussed. Optimization metrics of interest for different stakeholders in the fuel cycle (economics, fuel resource utilization, high level waste, transuranics/proliferation management, and environmental impact) are utilized for two different optimization techniques: a linear one and a stochastic one. Stakeholder elicitation provided sets of relative weights for the identified metrics appropriate to each stakeholder group, which were then successfully used to arrive at optimum fuel cycle configurations for recycling technologies. The stochastic optimization tool, based on a genetic algorithm, was used to identify non-inferior solutions according to Pareto's dominance approach to optimization. The main tradeoff for fuel cycle optimization was found to be between economics and most of the other identified metrics. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 246-253). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/79025 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/77061 Rotation generation and transport in tokamak plasmas Podpaly, Yuri Anatoly Plasma toroidal rotation is a factor important for plasma stability and transport, but it is still a fairly poorly understood area of physics. This thesis focuses on three aspects of rotation: momentum transport, Ohmic rotation reversals, and LHCD induced rotation. Momentum transport is approached in a semi-empirical method through the development of the "Toy Model." The "Toy Model" assumes that the toroidal momentum is transported via diffusive and convective profiles, and, using assumptions about the diffusive and convective terms, it can generate the profiles of the residual stress or source as a function of space and time. Several resultant source profile calculations are shown for SSEP sweeps, rotation reversals, H-modes, and I-modes. Generally, it is observed that the convective profiles do not greatly improve the fits to the data, and that source profiles have peaks around the steep core rotation gradient region of the plasma. Rotation reversals, spontaneous reversals of the rotation direction during the Ohmic phase, are also described in this work. It is seen that they are related to the Linear Ohmic Confinement (LOC) to Saturated Ohmic Confinement (SOC) regime changeover. This relation is supported through linear gyrokinetic simulations that show that the co- to counter- reversal coincides with a change from marginally electron to ion diamagnetic direction most unstable modes which is believed to play a role in the LOC to SOC explanation as well. Lower Hybrid Current Drive (LHCD) induced rotation is also described, including the first experimental observations of bi-directional rotation on a single tokamak. These observations help to explain differences in rotation seen among the various devices running lower hybrid. The LHCD rotation reverses direction as a function of plasma current, and this occurs in a similar parameter space as the Ohmic rotation reversal; it also has turbulence changes that are reminiscent of the Ohmic reversal as well. This suggests that LHCD is, in fact, causing the plasma to transition from the ITG dominated regime to the TEM dominated regime, which explains the rotation differences. These experiments and models provide new tools to understand rotation transport and generation in tokamaks. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 187-201). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/77061 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/77059 Energy system transformation : an evaluation of innovation requirements and policy options Finan, Ashley (Ashley E.) The U.S. government and others around the world have been exploring strategies to respond to climate change for nearly two decades. Consideration of these efforts as well as the 2010 oil spill in the Gulf of Mexico, the 2011 nuclear accident at Fukushima Daichi, and improved shale gas recovery methods are spurring debate on energy policy options. An important focus of this debate is the role of innovation in reducing carbon emissions while also maintaining the affordability of energy supplies. The scale of the required transition to a low-carbon energy system is large. A simple calculation scheme based on the Kaya identity is used to evaluate this transition and to estimate the magnitude of the changes that would be required. The recent performance of the U.S. economy with respect to decarbonization and energy intensity is shown to fall far short of future needs in low-carbon scenarios. The MARKAL model is used to estimate the magnitude of the capital investment required to transform the U.S. electric power sector. A comprehensive treatment of the innovation process must consider not only research and development but also the 'downstream' stages of demonstration, early adoption, and evolutionary post-commercialization improvements. Under greenhouse gas reduction scenarios, investments will be needed in low-carbon technologies when there is still considerable uncertainty and risk associated with their performance, and when they may not be competitive with incumbent energy systems. No less than investments in research and development, these are investments in innovation. A two-stage model of the innovation process is used to estimate the investment needed to bring a new technology to a competitive cost level. The model is used to explore the contributions of early-stage and later-stage investments in innovation, and illustrates the importance of the technological learning process. A case study of innovation in the nuclear energy industry is used to evaluate the effectiveness of alternative policies for driving investment in energy technologies more generally. The case study reveals a pattern of erratic policy that discouraged private investment. The use of technology-push rather than market-pull policy tools is found to have encouraged technology lock-in and discouraged market-driven innovation. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 311-326). Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/1721.1/77059 2012-01-01T00:00:00Z