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In this work the flexibility requirements of a highly renewable European electricity network that has to cover fluctuations of wind and solar power generation on different temporal and spatial scales are studied. Cost optimal ways to do so are analysed that include optimal distribution of the infrastructure, large scale transmission, storage, and dispatchable generators. In order to examine these issues, a model of increasing sophistication is built, first considering different flexibility classes of conventional generation, then adding storage, before finally considering transmission to see the effects of each.
To conclude, in this work it was shown that slowly flexible base load generators can only be used in energy systems with renewable shares of less than 50%, independent of the expansion of an interconnecting transmission network within Europe. Furthermore, for a system with a dominant fraction of renewable generation, highly flexible generators are essentially the only necessary class of backup generators. The total backup capacity can only be decreased significantly if interconnecting transmission is allowed, clearly favouring a European-wide energy network. These results are independent of the complexity level of the cost assumptions used for the models. The use of storage technologies allows to reduce the required conventional backup capacity further. This highlights the importance of including additional technologies into the energy system that provide flexibility to balance fluctuations caused by the renewable energy sources. These technologies could for example be advanced energy storage systems, interconnecting transmission in the electricity network, and hydro power plants.
It was demonstrated that a cost optimal European electricity system with almost 100% renewable generation can have total system costs comparable to today's system cost. However, this requires a very large transmission grid expansion to nine times the line volume of the present-day system. Limiting transmission increases the system cost by up to a third, however, a compromise grid with four times today's line volume already locks in most of the cost benefits. Therefore, it is very clear that by increasing the pan-European network connectivity, a cost efficient inclusion of renewable energies can be achieved, which is strongly needed to reach current climate change prevention goals.
It was also shown that a similarly cost efficient, highly renewable European electricity system can be achieved that considers a wide range of additional policy constraints and plausible changes of economic parameters.
In this thesis we study strongly correlated electron systems within the Density Functional Theory (DFT) in combination with the Dynamical Mean-Field Theory (DMFT).
First, we give an introduction into the theoretical methods and then apply them to study realistic materials. We present results on the hole-doped 122-family of the iron-based superconductors and the transition-metal oxide SrVO3. Our investigations show that a proper treatment of strong electronic correlations is necessary to describe the experimental observations.
Zur effizienten Beschleunigung von Ionen wird meist nach deren Erzeugung in einer Ionenquelle ein Radio Frequenz Quadrupol verwendet. Die vorliegende Dissertation befasst sich mit Entwicklung, Bau und Messung des Prototyps eines neuartigen Leiter-RFQs, der bei 325 MHz betrieben wird. Der Leiter-RFQ verfügt über ein neuartiges mechanisches Design und versucht die Vorteile der beiden vorrangig im Betrieb befindlichen RFQ Typen, des 4-Rod und 4-Vane RFQs, zu verbinden. Die physikalischen Parameter sind der Spezifikation des RFQs für den geplanten Protonenlinac (p-Linac) am FAIR-Projekt an der GSI Darmstadt entnommen. Darüber hinaus wird der aktuelle Planungs- und Simulationsstand eines modulierten Prototyps mit der vollen Länge von ca. 3,5 m zur Durchführung von Strahltests dargestellt.
The Facility for Antiproton and Ion Research (FAIR) at GSI Darmstadt will provide unprecedented intensities of protons and heavy ions up to uranium at energies of up to 29 GeV for protons and 2.7 GeV/u for Uranium 28+. To achieve high intensities in the synchrotron accelerators, high beam currents have to be provided by the injector linear accelerators. High current heavy ion beams are provided by the Universal Linear Accelerator (UNILAC), which in its current state will not be able to provide the required FAIR beam currents. This thesis deals with the development of upgrades for the UNILAC to ensure its high current capability. The first improvement is a matching section (MEBT) for the interface between the RFQ and the IH-DTL of the existing high current injector HSI at the UNILAC. With this new MEBT section, particle losses are eliminated and the overall beam quality is improved. As a second improvement, a complete replacement of the existing Alvarez-DTL is presented. A combination of efficient IH-type cavities and KONUS beam dynamics results in a reduction of the linac length from about 60 m (Alvarez) to just 23 m (new IH-DTL) while providing the same energy and fulfilling FAIR requirements of a high beam current and beam quality. This thesis contains a detailed beam dynamics design of the new linac including some fundamental investigations of the KONUS beam dynamics concept. A cross-check of the beam dynamics design was performed with two independent multi-particle simulation codes. Detailed error studies were conducted to investigate the influence of manufacturing, alignment and operating errors on the beam dynamics performance. Additionally, all five linac cavities were designed, optimized, and their RF parameters including power requirements calculated to provide a comprehensive linac design.
Development of the timing system for the Bunch-to-Bucket transfer between the FAIR accelerators
(2017)
The FAIR project is aiming at providing high-energy beams of ions of all elements from hydrogen to uranium, antiprotons and rare isotopes with high intensities. The existing accelerator facility of GSI and the future FAIR facility employ a variety of circular accelerators like heavy ion synchrotrons (SIS18 and SIS100) and storage rings (ESR, CRYRING, CR and HESR) for the preparation of secondary beams and experiments. Bunches are required to be transferred into rf buckets among GSI and FAIR ring accelerators for different purposes. Without the proper transfer, the beam will be subject to various beam quality deterioration and even to beam losses. Hence, the proper bunch-to-bucket (B2B) transfer between two rings is of great importance for FAIR and is the topic, which has been investigated in this thesis.
These circular accelerators of GSI and FAIR have different ratios in their circumference. For example, the circumference ratio between SIS100 and SIS18 is an integer and between SIS18 and ESR is close to an integer and between CR and HESR is far away from an integer. The ring accelerators are connected via a complicated system of beam transfer lines, targets for the secondary particle production and the high energy separators mentioned above. For FAIR, not only the primary beams are required to be transferred from one ring to another, but also the secondary beams, e.g. the antiproton or rare isotope beams produced by the antiproton (pbar) target, the fragment separator (FRS) or the superconducting fragment separator (Super-FRS). An important topic for this system of accelerators is the proper transfer of beam between the different circular accelerators. Bunches of one ring must be transferred into buckets of another ring within an upper bound time constraint (e.g. 10 ms for most FAIR use cases) and with an acceptable B2B injection center mismatch +-1 degree for most FAIR use cases). Hence, a flexible FAIR B2B transfer system is required to realize the different complex B2B transfers between the FAIR rings in the future. In the focus of the system development and of this thesis is the transfer from SIS18 to SIS100, which can be tested at GSI on the transfer from SIS18 to ESR and from ESR to CRYRING. The system is based on the existing technical basis at GSI, the low-level radio frequency (LLRF) system and the FAIR control system. It coordinates with the Machine Protection System (MPS), which protects SIS100 and subsequent accelerators and experiments from damage caused by high intensity primary beams in case of malfunctioning. Besides, it indicates the beam status and the actual beam injection time for the beam instrumentation and diagnostics.
The conceptual realization of the FAIR B2B transfer system was introduced in this thesis for the first time. It achieves the most FAIR B2B transfers with a tolerable B2B injection center mismatch (e.g. +-1 degree) and within an upper bound time (e.g. 10 ms). It supports two synchronization methods, the phase shift and frequency beating methods. It is flexible to support the beam transfer between two rings with different ratios in their circumference and several B2B transfers running at the same time, e.g. the B2B transfer from SIS18 to SIS100 and at the same time the B2B transfer from ESR to CRYRING. It is capable to transfer beam of different ion species from one machine cycle to another and to transfer beams between two rings via the FRS, the pbar target and the Super-FRS. It allows various complex bucket filling pattern. In addition, it coordinates with the MPS system, which protects the SIS100 and subsequent accelerators or experiments from beam induced damage.
A list of criteria for the preservation of beam qualities during the rf frequency modulation of the phase shift method was analyzed. As an example the beam reaction on three different rf frequency modulation examples were analyzed for SIS18 beams. According to the beam dynamic analysis, there is a maximum value for the rf frequency modulation. The first derivative of the rf frequency modulation must be continuous and small enough and the second derivative must be small enough.
In addition to the analysis from the viewpoint of beam dynamics, two test setups were built. The first test setup was used to characterize the FAIR timing network – white rabbit network for the B2B transfer. In the second test setup, the firmware of the FAIR B2B transfer system was evaluated, which was running on the soft CPU, LatticeMico32, of the Scalable Control Unit - the FAIR standard Front End Controller. Besides, the boundary conditions of the different trigger scenarios of the SIS18 extraction and SIS100 injection kicker magnets were investigated. Finally, the application of the FAIR B2B transfer system for all FAIR use cases was demonstrated.
The dissertation plays a significant important role for the realization of the FAIR B2B transfer system and the further practical application of the system to all FAIR use cases.
Compact stars can be treated as the ultimate laboratories for testing theories of dense matter. They are not only extremely dense objects, but they are known to be associated with strong magnetic fields, fast rotation and, in certain cases, with very high temperatures. Here, we present several different approaches to model numerically the signatures and properties of these stars, namely:
•The effects of strong magnetic fields on hybrid stars by using a fully general relativistic approach. We solved the coupled Maxwell-Einstein equations in a self-consistent way, taking into consideration the anisotropy of the energy-momentum tensor due purely to the magnetic field, magnetic field effects on equation of state and the interaction between matter and the magnetic field (magnetization). We showed that the effects of the magnetization and the magnetic field on the equation of state for matter do not play an important role on global properties of neutron stars (only the pure magnetic _eld contribution does). In addition, the magnetic field breaks the spherical symmetry of stars, inducing major changes in the populated degrees of freedom inside these objects and, potentially, converting a hybrid star into a hadronic star over time.
•The effects of magnetic fields and rotation on the structure and composition of proto-neutron stars. We found that the magnetic field not only deforms these stars, but also significantly alters the number of trapped neutrinos in the stellar interior, together with the strangeness content and temperature in each evolution stage from a hot proto-neutron star to a cold neutron star.
•The influence of the quark-hadron phase transitions in neutron stars. In particular, previous calculations have shown that fast rotating neutron stars, when subjected to a quark-hadron phase transition in their interiors, could give rise to the backbending phenomenon characterized by a spin-up era. In this work, we obtained the interesting backbending phenomenon for fast spinning neutron stars. More importantly, we showed that a magnetic field, which is assumed to be axisymmetric and poloidal, can also be enhanced due to the phase transition from normal hadronic matter to quark matter on highly magnetized neutron stars. Therefore, in parallel to the spin-up era, classes of neutron stars endowed with strong magnetic fields may go through a `magnetic-up era' in their lives.
•Finally, we were also able to calculate super-heavy white dwarfs in the presence of strong magnetic fields. White dwarfs are the progenitors of supernova Type Ia explosions and they are widely used as candles to show that the Universe is expanding and accelerating. However, observations of ultraluminous supernovae have suggested that the progenitor of such an explosion should be a white dwarf with mass above the well-known Chandrasekhar limit ~ 1.4 M. In corroboration with other works, but by using a fully general relativistic framework, we obtained also strongly magnetized white dwarfs with masses M ~ 2:0 M.
Terahertz (THz) physics are an emerging field of research dealing with electromagnetic radiation in the far-infrared to microwave region. The development of innovative technologies for the generation and detection of THz radiation has only in the recent past led to a tremendous rise of both fundamental research as well as investigation of possible fields of application for THz radiation. The most prominent reason has long been the scarce accessibility of the THz region of the electromagnetic spectrum - commonly loosely located between 0.1 and 30 THz - to broad research, and it was mostly limited to astronomy and high energy physics facilities. Over the recent years, numerous novel concepts on both the source and detector side have been proposed and successfully implemented to overcome this so-called THz gap. New technology has become available and paved the way for wide-spread experimental laboratory work and accompanying theoretical investigations. First application studies have emerged and in some cases even commercial development of the field of THz physics is on the rise. Despite these enormous progresses, a continuing demand for more efficient THz detectors still impels current technological research. Relatively low source powers are often a major limiting factor and the request for new detection concepts, their understanding and implementation, as well as the optimization on a device basis has been and still remains in place. One of these concepts is the use of field-effect transistors (FETs) high above their conventional cut-off frequencies as electronic THz detectors. The concept has been proposed in a number of theoretical publications by M. Dyakonov and M. Shur in the early 1990's, who pioneered to show that under certain boundary conditions, non-linear collective excitations of the charge carrier system of a two-dimensional electron gas (2DEG) by incident THz radiation can exhibit rectifying behaviour - a detection principle, which has become known as plasma wave or plasmonic mixing. Up until this day, the concept has been successfully implemented in many device realizations - most advanced in established silicon CMOS technology - and stands on the edge of becoming commercially available on a large scale. The main direction of the work presented in this thesis was the modeling and experimental characterization of antenna-coupled FETs for THz detection - termed TeraFETs in this and the author's previous works - which have been implemented in different material systems. The materials presented in this thesis are AlGaN/GaN HEMTs and graphene FETs. In a number of scientific collaborations, TeraFETs were designed based on a hydrodynamic transport model, fabricated in the respective materials, and characterized mainly in the lower THz frequency region from 0.2 to 1.2 THz. The theoretical description of the plasma wave mixing mechanism in TeraFETs, as initiated by Dyakonov and Shur, was based on a fluid-dynamic transport model for charge carriers in the transistor channel. The THz radiation induces propagating charge density oscillations (plasma waves) in the 2DEG, which via non-linear self-mixing cause rectification of the incident THz signals. Over the course of this work, it became evident in the on-going detector characterization experiments that this original theoretical model of the detection process widely applied in the respective literature does not suffice to describe some of the experimental findings in TeraFET detection signals. Thorough measurements showed signal contributions, which are identified in this work to be of thermoelectric origin arising from an inherent asymmetric local heating of charge carriers in the devices. Depending on the material, these contributions constituted a mere side effect to plasmonic detection (AlGaN/GaN) or even reached a comparable magnitude (graphene FETs). To include these effects in the detector model, the original reduced fluid-dynamic description was extended to a hydrodynamic transport model. The model yields at the current stage a reasonable qualitative agreement to the measured THz detection signals. This thesis presents the formulation of a hydrodynamic charge carrier transport model and its specific implementation in a circuit simulation tool. A second modeling aspect is that the transport equations cover only the intrinsic plasmonic detection process in the active gated part of the TeraFET's transistor channel. In order to model and simulate the behavior of real devices, extrinsic detector parts such as ungated channel regions, parasitic resistances and capacitances, integrated antenna impedance, and others must be considered. The implemented detector model allows to simulate THz detection in real devices with the above influences included. Besides presentation of the detector model, experimental THz characterization of the fabricated TeraFETs is presented in this work. Careful device design yielded record detection performance for detectors in both investigated materials. The respective results are shown and the experimental observations of the thermoelectric effect in TeraFETs are compared to modeling results. It is the goal of this work to provide a framework for further theoretical and experimental studies of the plasmonic and thermoelectric effect in TeraFETs, which could eventually lead to a new type of THz detectors particularly exploiting the thermoelectric effect to enhance the sensitivity of today's plasmonic TeraFETs.
In this doctoral thesis the transformation from relativistic hydrodynamics to transport and vice versa is studied. Approximations made by hybrid (hydrodynamics + transport) simulations of relativistic heavy ion collisions are discussed and their reliability is assessed at intermediate collision energies. A new method to simulate heavy ion collisions is suggested, based on the forced thermalization in high-density regions.
Diese Doktorarbeit widmet sich der Untersuchung von Systemen von Quarks und der Wechselwirkung zwischen ihnen mit Hilfe von Lattice QCD. Aus Quarks zusammengesetzte Objekte heißen Hadronen. Ein bestimmter Typ von Hadronen ist das sogenannten Tetraquark. In Teilchendetektoren wie dem LHCb in der Schweiz oder Belle in Japan wurden in jüngerer Zeit Zustände gefunden, die als Kandidaten für Tetraquarks gelten. Diese Arbeit befasst sich mit der Beschreibung und Untersuchung solcher Tetraquark-Zustände. Die Systeme, um die es in dieser Arbeit hauptsächlich geht, enthalten vier Quarks unterschiedlicher Masse. Zwei Quarks wird im Großteil der Arbeit eine unendlich große Masse zugeordnet. Zwei Quarks haben eine endliche Masse. In dieser statisch-leichten Näherung ist es möglich, das Potential der schweren Quarks in Anwesenheit der leichten Quarks zu bestimmen und zu überprüfen, ob es attraktiv genug dazu ist, einen gebundenen Zustand der vier Quarks zu bilden. Dieses Vorgehen ist als Born-Oppenheimer-Approximation bekannt. Die Observable, die berechnet werden muss, ist also das Vier-Quark-Potential.
Im ersten Teil der Arbeit werden verschiedene Vier-Quark-Potentiale aufgeführt und die zugehörigen Quantenzahlen genannt. Jeder der geeigneten Kanäle wird auf seine Fähigkeit untersucht, einen gebundenen Zustand zu bilden. Eine ausführliche systematische und statistische Analyse liefert den eindeutigen Befund, dass Bindung nur für Isospin I = 0 und nichtstatistsche u- und d-Quarks möglich ist. Im Falle von I = 1 oder nichtstatistschen s- und c-Quarks ist kein gebundener Zustand zu erwarten. Schließlich wird für den Fall der u- und d-Quarks eine Extrapolation zu physikalischen Quarkmassen durchgeführt. Die Bindung wird mit abnehmender Quarkmasse stärker. Am physikalischen Punkt wird eine Bindungsenergie von −90(+43−36) MeV festgestellt. Somit wird für Quantenzahlen I(J^P) = 0(1^+) ein gebundener b̄b̄ud-Zustand postuliert. Im zweiten Teil der Arbeit wird die statisch-leichte Näherung aufgehoben. So kann der Spin der schweren Quarks einbezogen werden. Dies führt unter anderem dazu, dass B- und B* -Mesonen unterscheidbar werden. Ein Nachteil dessen, dass vier Quarks endlicher Masse verwendet werden, ist der, dass es nun nicht mehr möglich ist, das Potential der schweren Quarks in Gegenwart der leichten zu bestimmen. Stattdessen wird aus der Korrelationsfunktion des Vier-Quark-Zustands direkt die Masse bestimmt. Zur Beschreibung der schweren Quarks wird der Ansatz der Nichtrelativistischen QCD (NRQCD) gewählt. Es wird der aus dem ersten Teil bekannte gebundene b̄b̄ud-Zustand mit Quantenzahlen I(J^P) = 0(1^+) weiter untersucht. Wir nehmen an, dass die Quantenzahlen durch ein BB*-Molekül realisiert werden. Wir bestimmen mithilfe des generalisierten Eigenwertproblems (GEP) den Grundzustand. Die Masse des Grundzustands ist ein Hinweis auf die Existenz eines gebundenen Zustands. Insgesamt bekräftigt der Befund das im ersten Teil der Arbeit gefundene Resultat, die Vorhersage eines bisher nicht gemessenen Tetraquark-Zustandes, qualitativ. Im dritten Teil der Arbeit geht es um Vier-Quark-Systeme, die ein schweres Quark und ein schweres Antiquark sowie ein leichteres Quark und ein leichteres Antiquark enthalten. Neben einem gebundenen Vier-Quark-Zustand ist u.a. die Bildung eines Bottomonium-und-Pion-Zustands möglich. Dies macht die theoretische Beschreibung dieses Systems ungleich schwieriger als die Beschreibung des im ersten und zweiten Teil der Arbeit untersuchten Systems. Seine experimentelle Untersuchung hingegen ist weniger aufwändig. So wurden bereits Kandidaten für einen solchen Zustand gemessen: Z_b(10610) und Z_b(10650). Zunächst wird ein Szenario beschrieben, in welcher Reihenfolge die zu den verschiedenen Strukturen gehörenden Potentiale vorliegen. So handelt es sich bei dem Grundzustandspotential des Systems um das Potential eines unangeregten Bottomonium-Zustands mit einem Pion in Ruhe. Darüber liegen zahlreiche Bottomonium-Zustände mit Pionen mit endlichem Impuls. Inmitten dieser Potentiale liegt gegebenenfalls das gesuchte Tetraquark-Potential. Ziel ist, einen Weg zu finden, die Bottomonium-und-Pion-Potentiale und das Tetraquark-Potential voneinander zu unterscheiden. Im ersten Schritt wird der Bottomonium-und-Pion-Grundzustand mithilfe des GEP aus dem System entfernt. Der erste angeregte Zustand ist im Anschluss daran weitgehend frei von Einflüssen des Grundzustands. Man findet, dass das Potential des ersten angeregten Zustandes attraktiv ist, sodass die Bildung eines Tetraquark-Zustandes nicht ausgeschlossen ist. Um den ersten angeregten Zustand weiter zu untersuchen, wird ein quantenmechanisches Modell verwendet, das die Volumenabhängigkeit des Überlapp eines Testzustands mit den verschiedenen Strukturen beschreibt. Es damit prinzipiell möglich, unter Zuhilfenahme mehrerer Gittervolumina eine Aussage über die Struktur des ersten angeregten Zustands zu treffen.