Hydropower has been around for more than a century and is considered a mature technology, but with recent advancements in power electronics and simulation capability new exciting ways to increase efficiency and reliability is possible. At Uppsala University a brushless exciter has been constructed for the experimental test rig, SVANTE. Power electronics are mounted on the shaft for control of the generator's excitation current. In addition a wireless control and measurement system is needed to provide the desired switching patterns to the power electronics and to evaluate performance of the system. In this thesis a shaft mounted embedded system for control and measurement is constructed as well as magnetic field sensors with measurement range up to 700mT. The computational power comes from a National Instruments sbRIO-9606. The system has 14 individual totem pole power electronics driving channels, 48 analog input channels for current signals and it communicates wirelessly through a bluetooth connection. The system is tested and works satisfactory but has not been mounted on the rotating side of the generator due to delays in the manufacturing.

Graphene, the two-dimensional lattice of sp2-hybridized carbon atoms, has a great potential for future electronics, in particular for opto-electronic devices. The carrier relaxation dynamics, which is of key importance for such applications, is in the main focus of this thesis. Besides a short introduction into the most prominent material properties of graphene and the experimental techniques, this thesis is divided into three main parts. The investigation of the carrier relaxation dynamics in the absence of a magnetic field is presented in Chapter 3. In the first experiment, the anisotropy of the carrier excitation and relaxation in momentum space was investigated by pump-probe measurements in the near-infrared range. While this anisotropy was not considered in all previous experiments, our measurements with a temporal resolution of less than 50 fs revealed the polarization dependence of the carrier excitation and the subsequent relaxation. About 150 fs after the electrons are excited, the carrier distribution in momentum space gets isotropic, caused by electron-phonon scattering. In a second set of two-color pump-probe experiments, the temperature of the hot carrier distribution, which was obtained within the duration of the pump pulse (about 200 fs), could be estimated. Furthermore, a change in sign of the pump-probe signal can be used as an indicator for the Fermi energy of different graphene layers. Pump-probe experiments in the far-infrared range in reflection and transmission geometry were performed at high pump power. A strong saturation of the pump-induced transmission was found in previous experiments, which was attributed to the pump-induced change in absorption. Our investigation shows the strong influence of pump-induced reflection at long wavelengths, as well as a lot smaller influence of the saturation of the pump-induced change in absorption. At a high pump power, the increase of the reflection exceeds the change in absorption strongly, which leads to negative pump-probe signals in transmission geometry. In Chapter 4, investigations of the carrier dynamics of graphene in magnetic fields of up to 7T are presented. Even though the optical properties of Landau-quantized graphene are very interesting, the carrier dynamics were nearly unexplored. A low photon energy of 14meV allows the investigation of the intraband Landau-level (LL) transitions. These experiments revealed two main findings: Firstly, the Landau quantization strongly suppresses the carrier relaxation via optical-phonon scattering, resulting in an increased relaxation time. Secondly, a change in sign of the pump-probe signal can be observed when the magnetic field is varied. This change in sign indicates a hot carrier distribution shortly after the pump pulse, which means that carrier-carrier scattering remains very strong in magnetic fields. In a second set of pump-probe measurements, carried out at a photon energy of 75meV, the relaxation dynamics of interband LL transitions was investigated. In particular, experiments on the two energetically degenerate LL transitions LL(−1)->LL(0) and LL(0)->LL(1) showed the influence of extremely strong Auger processes. An ultrafast and extremely broadband terahertz detector, based on a graphene flake, is presented in the last chapter of this thesis. To couple the radiation efficiently to the small flake, the inner part of a logarithmic periodic antenna is connected to it. With a rise time of about 50 ps in a wavelength range of 9 μm to 500 μm, this detector is very interesting to obtain the temporal overlap in two-color pump-probe experiments with the free-electron laser FELBE. Furthermore, the importance of the substrate material, in particular for the high-speed performance, is discussed.

Fusion neutrons from high energy density plasmas generated by pulsed laser irradiation of nanoscale atomic clusters have been explored in recent experiments at the University of Texas at Austin. A sufficiently strong (~200 T) magnetic field is expected to produce a magnetized, high temperature (10 keV) plasma with beta [approximately equal to] 1. Such a field along the laser axis may confine the plasma’s radial expansion, thus increasing fusion yield. As part of a multi-stage project to implement this experiment, a scaled (~40 T, ~500 KA) version of the final 200 T, 2.2 MA pulsed power device has been designed and built by Sandia National Laboratories and is now at UT-Austin. This apparatus, named MegaGauss, is meant to serve as a preparation tool for the 200 T system; as such, its current pulse was recorded for analysis, and is compared to a theoretical model to verify its response parameters (e.g. peak current, time to peak). Techniques and results of this comparison are discussed, followed by explanations of basic construction of the 40 T device and current sensing instrumentation. Discussion of MegaGauss is completed with a survey of notable failure modes, and a description of the often severe effects the miniature field-generating Helmholtz coil experiences due to the current pulse and magnetic field. Finally, a novel data archive scheme, structured around the familiar MDSplus archive system, is implemented in Labview and integrated into the main pulsed power control program. Specifically, methods for linking MDSplus’s robust functionality with Labview’s intuitive development environment are realized by means of a specialized software bridge between the two. These methods are used in software that allows MDSplus archives to be written and read exclusively through Labview. / text

For some cases of lattice layout in particle accelerators, the major part of the energy deposition coming from the collision is located in the midplane of the magnets. The heat produced might result in a quench in superconducting magnets. One solution for reducing the energy deposition in the coil is to introduce an opening in the midplane, which will lead away most of the particles to a safe zone instead of hitting the superconductors in the magnets. The aim of this work is to optimize the field quality in dipoles based on the cosθ-design, where an opening in the midplane has been inserted. The equations for finding the solutions for the coil layout for different sizes of the opening are studied, and the solution giving the best field quality for each case is presented. Then, optimization procedures are applied to lay-outs with Rutherford cables. Finally, the resulting field strength from the solutions obtained is presented.

Disertacijoje nagrinėjami stipraus impulsinio magnetinio lauko induktoriai, kurių ilgaamžiškumas priklauso nuo daugelio jų fizikinių parametrų. Sukūrus induktorių geometrijos sintezės metodiką, sudaryti induktorių matematiniai ir kompiuteriniai modeliai, ištirti impulso metu skirtingų parametrų induktorių apvijose vykstantys procesai, atlikta daugkartinio naudojimo induktorių geometrijų paieška. Sukurtas programinis aprūpinimas induktorių skaičiavimams įgalina nustatyti induktorių, tinkamų daugkartiniam impulsiniam magnetiniam laukui generuoti, parametrus. Darbo rezultatai pritaikyti kuriant induktorių prototipus. Disertaciją sudaro įvadas, keturi skyriai, bendrosios išvados, literatūros ir publikacijų disertacijos tema sąrašas. Įvadiniame skyriuje aprašomas problemos aktualumas, formuluojamas darbo tikslas ir uždaviniai, pristatomi autoriaus pranešimai ir publikacijos, pateikiama disertacijos struktūra. Pirmajame skyriuje aptariama stipraus magnetinio lauko reikšmė šiuolaikiniam mokslui, pristatomi stipraus magnetinio lauko generavimo būdai, analizuojami impulsiniai induktoriai, jų kompiuterinių modelių sudarymo problematika, geometrijos optimizavimas. Antrajame skyriuje aprašoma induktorių geometrijos ir medžiagų sudėties sintezės metodika, sukuriamas induktoriaus matematinis-kompiuterinis modelis, apibrėžiama daugkartinio naudojimo induktorių pagrindinių parametrų visuma – „gyvavimo zona“, pateikiamas daugkartinio naudojimo induktorių geometrijų paieškos algoritmas... [toliau žr. visą tekstą] / The aim of the dissertation is the analysis of high pulsed magnetic field inductors in order to determine their electrophysical parameters for non-destructive magnetic field generation. To obtain that effective method to synthesize inductor geometrical and material models was developed, inductor mathematical and computer models created, electrophysical processes during the pulse in windings of various inductors were examined. Finally, retrievals of nondestructive inductor geometrical configurations were performed. Software developed and results gained were successfully used to design new pulsed inductor prototypes. Dissertation content: introduction, four chapters, general conclusions, list of references and list of author’s publications on the subject of dissertation. The introduction contains the topicality of the problem, aim of the work, main tasks, scientific novelty, practical value, result approval, defended statements and structure description. Overview of different high magnetic field generation techniques, pulsed inductor design, geometry optimization problems and software used for these tasks are the objectives of the first chapter. The second chapter is dedicated to development of technique for inductor geometrical-material model synthesis, creation of mathematical-computer inductor model, definition of long-life operation inductor parameters – their “vitality zone” and design of non-destructive inductor geometries retrieval algorithm. In the third chapter... [to full text]

The aim of the dissertation is the analysis of high pulsed magnetic field in-ductors in order to determine their electrophysical parameters for non-destructive magnetic field generation. To obtain that effective method to synthe-size inductor geometrical and material models was developed, inductor mathe-matical and computer models created, electrophysical processes during the pulse in windings of various inductors were examined. Finally, retrievals of non-destructive inductor geometrical configurations were performed. Software de-veloped and results gained were successfully used to design new pulsed inductor prototypes. Dissertation content: introduction, four chapters, general conclusions, list of references and list of author’s publications on the subject of dissertation. The introduction contains the topicality of the problem, aim of the work, main tasks, scientific novelty, practical value, result approval, defended state-ments and structure description. Overview of different high magnetic field generation techniques, pulsed in-ductor design, geometry optimization problems and software used for these tasks are the objectives of the first chapter. The second chapter is dedicated to development of technique for inductor geometrical-material model synthesis, creation of mathematical-computer induc-tor model, definition of long-life operation inductor parameters – their “vitality zone” and design of non-destructive inductor geometries retrieval algorithm. In the third chapter... [to full text] / Disertacijoje nagrinėjami stipraus impulsinio magnetinio lauko induktoriai, kurių ilgaamžiškumas priklauso nuo daugelio jų fizikinių parametrų. Sukūrus induktorių geometrijos sintezės metodiką, sudaryti induktorių matematiniai ir kompiuteriniai modeliai, ištirti impulso metu skirtingų parametrų induktorių ap-vijose vykstantys procesai, atlikta daugkartinio naudojimo induktorių geometrijų paieška. Sukurtas programinis aprūpinimas induktorių skaičiavimams įgalina nustatyti induktorių, tinkamų daugkartiniam impulsiniam magnetiniam laukui generuoti, parametrus. Darbo rezultatai pritaikyti kuriant induktorių prototipus. Disertaciją sudaro įvadas, keturi skyriai, bendrosios išvados, literatūros ir publikacijų disertacijos tema sąrašas. Įvadiniame skyriuje aprašomas problemos aktualumas, formuluojamas dar-bo tikslas ir uždaviniai, pristatomi autoriaus pranešimai ir publikacijos, patei-kiama disertacijos struktūra. Pirmajame skyriuje aptariama stipraus magnetinio lauko reikšmė šiuolaiki-niam mokslui, pristatomi stipraus magnetinio lauko generavimo būdai, analizuo-jami impulsiniai induktoriai, jų kompiuterinių modelių sudarymo problematika, geometrijos optimizavimas. Antrajame skyriuje aprašoma induktorių geometrijos ir medžiagų sudėties sintezės metodika, sukuriamas induktoriaus matematinis-kompiuterinis modelis, apibrėžiama daugkartinio naudojimo induktorių pagrindinių parametrų visuma – „gyvavimo zona“, pateikiamas daugkartinio naudojimo induktorių geometrijų paieškos algoritmas... [toliau žr. visą tekstą]

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The Qweak experiment at Thomas Jefferson National Accelerator Facility (Jefferson Lab) will measure the proton's weak charge by measuring the parity violating asymmetry in elastic electron-proton scattering at very low momentum transfer, with the aim of determining the proton's weak charge with 4% combined statistical and systematic errors. The experimental apparatus includes a longitudinally polarized electron beam, a liquid hydrogen target, a room temperature toroidal magnetic spectrometer, and a set of precision detectors for the scattered electrons. The toroidal magnetic spectrometer, which will deflect away the inelastic scattered electrons and focus the elastic scattered electrons onto the detectors, plays a crucially important role in the experiment. In this thesis, in order to meet the requirements for the installation and calibration of the toroidal magnetic spectrometer, the numerical simulation of the spectrometer's magnetic field based on a realistic magnet model is discussed, a precise 3D field mapping is introduced, and some simulation results are provided. The zero-crossing analysis technique, which can be used to precisely infer the individual coil locations of the toroidal magnet, is presented and explored in detail.

The existence of a Fisk-type heliospheric magnetic field (HMF) is one of the most debated questions in cosmic-ray modulation. Recently, Burger and Hitge [2004] developed a divergence-free Fisk-Parker hybrid magnetic field model to demonstrate the behaviour of cosmic rays in the heliosphere due to such a field. This approach has been refined and the properties of the consequent field are investigated. It is found that randomly directed magnetic field diffusion in and above the photosphere significantly influences the solar magnetic field both at the solar poles and near the polar coronal hole boundary. The solar cycle dependence of this field is investigated, a study which is of particular importance for studies of the long-term behaviour of cosmic rays, such as those undertaken at the SANAE base in Antarctica. The amplitudes of the 26-day recurrent cosmic-ray variations are modelled as function of both latitudinal gradient and heliolatitude and are found to agree qualitatively and in some cases quantitatively with the observational results reported by Zhang 119971 and Paizis et al. 119991. Although magnetic field data do not clearly indicate the existence of the Fisk field [see, e.g., Fursyth et al., 20021, this study supports the existence of a Fisk-type HMF. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2006.

Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2008.