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Coming dissertations at Uppsala university

  • High Power Radio Frequency Solid-State Amplifiers and Combiners for Particle Accelerators : From module to system design approach Author: Long Hoang Link: Publication date: 2019-12-20 13:13

    The rise of Big Science projects brings issues related to the energy consumption and the associated environmental impacts of such large-scale facilities. Therefore, environmentally-sustainable developments are undertaken towards the adoption of energy savings and improved energy-efficient approaches. The advent of the superconducting (SC) radio frequency (RF) accelerating cavity is bringing answers to these issues. Such superconducting RF (SRF) cavity is made of niobium that allows much higher accelerating gradients with a minimization of the energy consumption. The SC RF technology is increasingly used in many modern particle accelerators, including: the European Spallation Source (ESS), the X-ray Free Electron Laser (XFEL), the Linac Coherent Light Source (LCLS)-II and the proposed International Linear Collider (ILC).

    The innovation of solid state PA technology pushes limits regarding packaging, efficiency, frequency capability, thermal stability, making them more attractive than other well-established alternative technologies, such as vacuum tube technology in mid-range power applications. Through the investigations of designs and techniques, this research goal of the thesis allows to improve solid-state based power generation systems from module to the overall system design. This thesis introduces the single-ended PA design approach in planar technology and at kilowatt level. The design solution unlocks different possibilities including: improved integration, layout flexibility for tuning, and suitably for mass productions that are demanded in future high peak power generation systems. The novel amplifier design is followed by time domain characterization to fully evaluate the pulse profiles of such amplifiers when delivering kilowatt output power level for operation in conjunction with SRF accelerating cavities. Amplitude and phase stability of those amplifiers are also investigated in time-domain. The extracted data can then be used as measurement-based model for predicting factors which could degrade the overall stability of the associated PA.

    Future RF power generation systems built around solid state PAs need also efficient combining strategies. Two engineering design solutions are investigated in this thesis aiming for mid- and high- range power combination. One solution is based on a combination of the Gysel structure using suspended strip-line technology for improved power handling capability. Another solution is implementing a radial combiner, which uses re-entrant cavity resonator at 352 MHz and door-nob geometry for coupling at inputs and at the output. These solutions facilitate the scaling up 400 kW for powering ESS spoke cavities while maintaining a high degree of efficiency in RF power generation. This thesis gives insights of system integration and tuning procedures with a demonstration of combining 8 modules, delivering a total of 10 kW output power. Along with the proposed combining solutions at higher power levels, the nominal power block of 10 kW is used as an elementary block to propose scaling up in power till the 400 kW nominal power required by ESS.

    Finally, this thesis focuses on implementing an optimal charging scheme for SRF cavities, which helps reducing the wasted energy and improves the overall efficiency operation at future accelerating facilities. Therefore, these results contribute further to the larger adoption of solid state technologies in the future power generation systems for particle accelerators.

  • Zebrafish models for large-scale genetic screens in dyslipidemia and atherosclerosis : Validation and application Author: Manoj Kumar Bandaru Link: Publication date: 2019-12-20 09:02

    Hundreds of loci have been robustly associated with circulating lipids, atherosclerosis and coronary artery disease; but for most loci the causal genes and mechanisms remain uncharacterized. The overall aim of my thesis is to develop and validate novel in vivo model systems that are suitable for high-throughput, image-based genetic screens in coronary artery disease and related traits, and use these model systems to systematically characterize positional candidate genes.

    In Study I, I developed an experimental pipeline to validate the suitability of zebrafish larvae as a model system for systematic, large-scale characterization of drugs and genes associated with dyslipidemia and atherosclerosis. Using this pipeline, I showed that five days of overfeeding and cholesterol supplementation have independent pro-atherogenic effects in zebrafish larvae, which could be diminished by concomitant treatment with atorvastatin and ezetimibe. CRISPR-Cas9-induced mutations in orthologues of proof-of-concept genes resulted in higher LDL cholesterol levels (apoea), and more early stage atherosclerosis (apobb.1). Finally, the pipeline helped me to identify putative causal genes for circulating lipids and early-stage atherosclerosis (LPAR2 and GATAD2A).

    In Study II, I characterized cardiometabolic traits in apoc2 mutant zebrafish larvae and found that, similar to humans, larvae with two non-functional apoc2 alleles have higher whole-body levels of triglycerides and total cholesterol, and more vascular lipid deposition than larvae without mutations in apoc2. Interestingly, apoc2 mutant larvae also had lower glucose levels after adjusting for triglyceride levels, suggesting that therapeutic stimulation of apoc2 to prevent hypertriglyceridemia may result in hyperglycemia. Still, zebrafish larvae with mutations in apoc2 can be a useful model to identify and characterize additional causal genes for triglyceride metabolism.

    In Study III, I examined the effects of mutations in pcsk9 on atherosclerosis and diabetes-related traits in nearly 5,000 zebrafish larvae. Similar to the loss-of-function mutations in PCSK9 in humans, larvae with mutations in pcsk9 had lower LDLc levels and were protected from early-stage atherosclerosis. Interestingly, mutations in pcsk9 also resulted in fewer pancreatic β-cells in 10 days old larvae, which suggests the higher risk of diabetes in humans with mutations in PCSK9 may result from a direct effect on the beta cell.

    Based on these large-scale proof-of-concept studies, my thesis confirms that zebrafish larvae can be used for large-scale, systematic genetic screens in dyslipidemia and early-stage atherosclerosis.

  • Synthesis and Tuning of Multifunctional Materials at High Pressure Author: Lei Liu Link: Publication date: 2019-12-19 13:38

    At the present stage, human society is developing at an unprecedented speed, facing an emergence of highly pressing challenges, e.g., information explosion, energy production problems, environmental pollution, climate problems. Functional materials with tailored properties are considered as holding a key to solving these problems. In this thesis, high-pressure techniques were employed to synthesize and tune the properties of multiferroic materials relevant to spintronic and light-harvesting applications, and multifunctional high-entropy alloys.

    Melanostibite (Mn2FeSbO6, MFSO) is a very rare mineral discovered in Sweden. Previous studies indicate it is a potential multiferroic material with foreseen applications in information storage and spintronic devices. However, its multiferroic phase has not been synthesized yet. Herein, the structural evolution of MFSO was studied up to ~50 GPa, and the LiNbO3-type MFSO was synthesized at high pressure and moderate temperature. As a polar structure material, the LiNbO3-type MFSO represents a promising candidate for multiferroic materials. The double perovskite, Pb2CoTeO6, was also compressed to ~60 GPa, while no polar phase was discovered. The obtained results provide guidance to the synthesis of new multiferroic double perovskite.

    Solar energy is a promising alternative to fossil fuels and thus a viable solution to the global energy problem. Light-harvesting materials, which absorb sunlight and transform it into electricity by the photovoltaic effect, represent the core part of solar cells. Currently, the dominant commercial light-harvesting material is silicon. However, silicon and recently emerged organic-inorganic perovskites have several drawbacks. Multiferroic oxides are considered as stable and nontoxic light-harvesting materials. But, their bandgap energies are generally too large for photovoltaic applications. Herein, high-pressure technique was applied to treat Mn3TeO6, and a quenchable phase of Mn3TeO6 displaying a greatly narrowed bandgap was synthesized. The measured absorption spectrum of the quenched phase reveals that it may be suitable for photovoltaic applications. The present research opens a green way to tune the bandgap energy of multiferroic.

    High-entropy alloys (HEAs) were first synthesized in 2004. However, knowledge of this new class of promising alloys is still very limited, even in very fundamental aspects. The present results reveal that lattice distortion plays important roles in the phase transition of HEAs, and demonstrate the future possibility of designing the Invar high-entropy alloy, a promising structural material. The results show that it is possible to combine several practical properties in a single alloy, which will widen the range of applications of HEAs. 

    The presented research demonstrates that high-pressure represents an effective way to tune various properties of materials, as well as can be applied for the synthesis of materials with exotic properties which are usually not stable or attainable at ambient conditions.