Dielectric strength behaviour and mechanical properties of transparent insulation materials suitable to optical monitoring of partial discharges

[no abstract

Development of a SQUID magnetometry system for cryogenic neutron electric dipole moment experiment

A measurement of the neutron electric dipole moment (nEDM) could hold the key to understanding why the visible universe is the way it is: why matter should predominate over antimatter. As a charge-parity violating (CPV) quantity, an nEDM could provide an insight into new mechanisms that address this baryon asymmetry. The motivation for an improved sensitivity to an nEDM is to find it to be non-zero at a level consistent with certain beyond the Standard Model theories that predict new sources of CPV, or to establish a new limit that constrains them. CryoEDM is an experiment that sought to better the current limit of $|d_n| < 2.9 \times 10^{-26}\,e\,$cm by an order of magnitude. It is designed to measure the nEDM via the Ramsey Method of Separated Oscillatory Fields, in which it is critical that the magnetic field remains stable throughout. A way of accurately tracking the magnetic fields, moreover at a temperature $\sim 0.5\,$K, is crucial for CryoEDM, and for future cryogenic projects. This thesis presents work focussing on the development of a 12-SQUID magnetometry system for CryoEDM, that enables the magnetic field to be monitored to a precision of $0.1\,$pT. A major component of its infrastructure is the superconducting capillary shields, which screen the input lines of the SQUIDs from the pick up of spurious magnetic fields that will perturb a SQUID's measurement. These are shown to have a transverse shielding factor of $> 1 \times 10^{7}$, which is a few orders of magnitude greater than the calculated requirement. Efforts to characterise the shielding of the SQUID chips themselves are also discussed. The use of Cryoperm for shields reveals a tension between improved SQUID noise and worse neutron statistics. Investigations show that without it, SQUIDs have an elevated noise when cooled in a substantial magnetic field; with it, magnetostatic simulations suggest that it is detrimental to the polarisation of neutrons in transport. The findings suggest that with proper consideration, it is possible to reach a compromise between the two behaviours. Computational work to develop a simulation of SQUID data is detailed, which is based on the Laplace equation for the magnetic scalar potential. These data are ultimately used in the development of a linear regression technique to determine the volume-averaged magnetic field in the neutron cells. This proves highly effective in determining the fields within the $0.1\,$pT requirement under certain conditions

Aspects on measuring electrical current utilizing magnetic zero-flux technique

The utilization of high accuracy measurements of electrical quantities is a prerequisite for the development of modern society. Generally, measurements serve different purposes and hence the criteria for the measurement equipment and method are different. For example, the demands are mild if the application is the continuous monitoring of the power grid, more finely tuned for measuring methods used in research and development, and often challenging in the case of certified measuring methods adequate for calibration and accreditation. RISE Research Institutes of Sweden (former SP Technical Research Institute of Sweden) is appointed the National Metrology Institute by the Swedish government for electrical quantities and continuously develops and provides measurement technology for the different needs governed by application.The magnetic zero-flux technique is a non-contact measurement method for electrical AC and DC current and its design principle enables accurate measurements over a large current range. Its advantages come however with the price of a complex but sophisticated design. The zero-flux technique has been utilized for many decades, and there are a number of manufacturers providing commercial systems with somewhat different features.This project is devoted to the further investigation and advancement of some metrological aspects of the magnetic zero-flux technique for AC. Practical laboratory tests on a state-of-the-art zero-flux system are used to create a picture of its properties at higher frequencies than its manufacturer has provided detailed specifications for. Focus is to determine how sensitive the measurement results are to practical arrangements and limitations of the measurement setup. A method and guide to how different configurations of the measurement setup affect the measured results in different frequency ranges is provided. Utilizing this characterization, practical set-ups can be made, as optimal as possible for the frequency range of interest, avoiding time-consuming focus on aspects not relevant for the specific application.The identified aspects of interest are: (i) identifying the source of the measurement error in the zero-flux system’s design and, if possible, minimizing this error by design adjustments, (ii) measurement error and measurement uncertainty of a zero-flux system in presence of geometric asymmetry and disturbance from return or nearby conductors, (iii) simultaneous measurements of sinusoidal signals of different amplitudes, frequencies and phase angles, (iiii) detection of sub-synchronous events, and (v) non-steady state phenomena, like for example transients in the drive line of electrical vehicles. In this thesis, aspects (i) and (ii) above are in focus. Some conclusions can be drawn based on the performed study concerning aspect (iiii), whereas aspects (iii) and (v) remain out of its scope.The initial step of this project was the choice of a generally applicable method for characterization and evaluation of a zero-flux system. The method chosen is the combination of a coaxial primary current path, or as near coaxial as was practically convenient, and a Digital Sampling Watt Meter (DSWM). The method can be utilized for the characterization and evaluation of other zero-flux systems. An investigation was performed to decide from which part of the construction the phase angle error stems. The performed characterization allowed compensating for the errors, making the measurement accuracy greatly improved. Two modifications to the circuitry of the zero-flux systems were introduced and evaluated, both of which yielded improvement of its high frequency characteristics up to 100 kHz. Also the accuracy within the low frequency range (from 10 – 50 Hz) was improved by one of the modifications.The error of a zero-flux measuring system depends on the positioning of its sensor around the conductor carrying the measured current and the geometry of the primary current path. The total error increases with frequency, but which geometric factor that is the most important one varies with frequency. In this study, utilizing sinusoidal primary current, it was found that for 50 Hz, tilt of the sensor and positioning of the connection point for the measurement and zero-flux control cable (rotation) caused the largest effects on the scale factor. De-centring and the distances to different parts of the return conductor were less important in the 50 Hz case. For 25 kHz, de-centring and rotation were the main contributors to scale factor change, while tilt had the smallest measured effect. The total contribution from sensor positioning in the magnetic field to the expanded measurement uncertainty was estimated to 0.0024 % in the 50 Hz case, to 0.0040 % for 1 kHz, to 0.14 % for 10 kHz, and to 0.41 % for 25 kHz

Hardware and Methods for Scaling Up Quantum Information Experiments

Quantum computation promises to solve presently intractable problems, with hopes of yielding solutions to pressing issues to society. Despite this, current machines are limited to tens of qubits. The field is in a state of continuous scaling, with groups around the world working on all aspects of this problem. The work of this thesis aims to contribute to this effort. It is motivated by the goal of increasing both the speed and bandwidth of experiments conducted within our laboratory. Low-loss radio-frequency multiplexers were characterised at cryogenic temperatures, with some shown to operate at below 7mK. The Analog Devices ADG904 was one of these, and its insertion loss was measured at <0.5dB up to 2GHz. Their heat load was measured, and it was found that a switching speed of 10 MHz with an RF signal power of -30dB dissipates 43uW. Installing these switches yields a benefit over installing extra cabling in our cryostat for a switching speed of up to 2MHz and RF power of -30dBm. A switch matrix was prototyped for cryogenic operation, enabling re-routing of wiring inside a cryostat with a minimally increased thermal load. This could be used to significantly increase the scale of high frequency experiments. This switch has also been embedded within a calibration routine, facilitating measurement of a specific feature of interest at millikelvin temperatures. As the field of quantum engineering scales, such measurements will be crucial to close the loop, providing feedback to fabrication and semiconductor growth efforts. Finally, a rapid-turnaround test rig has been developed which has 32 high frequency and 100 DC lines, enabling tests of significant scale in liquid helium. This reduces the time per experiment at 4.2 K to hours rather than days, enabling tests such as thermal cycling, as well as the evaluation of on-chip structures or active electronics and classical computing hardware; which are all necessary elements of any solid state quantum computing architecture

The Environment and Interactions of Electrons in GaAs Quantum Dots

At the dawn of the twentieth century, the underpinnings of centuries-old classical physics were beginning to be unravelled by the advent of quantum mechanics. As well as fundamentally shifting the way we understand the very nature of reality, this quantum revolution has subsequently shaped and created entire fields, paving the way for previously unimaginable technology. The quintessential instance of such technology is the quantum computer, whose building blocks - quantum bits, or qubits - are premised on the uniquely quantum principles of superposition and entanglement. It is predicted that quantum computers will be capable of efficiently solving certain classically intractable problems. To build a quantum computer, it is necessary to find a system which exhibits these uniquely quantum phenomena. The success of silicon-based integrated circuits for classical computing made semiconductors an obvious architecture in which to focus experimental quantum computing efforts. The two-dimensional electron gas which forms at the interface of GaAs/AlGaAs heterostructures constitutes an ideal platform for isolating and controlling single electrons, encoding quantum information in their spin and charge states. This thesis broadly addresses three key challenges to quantum computing with GaAs qubits: scalability, particularly in the context of readout, unwanted interactions between fragile quantum states and their environment, and the facilitation of controllable, strong interactions between separated qubits as a means of generating entanglement. These significant, unavoidable challenges must be addressed in order for a future solid-state quantum computer to be viable

Highly-sensitive measurements with chirped- pulse phasesensitive OTDR

Distributed optical fiber sensing is currently a very predominant research field, which perceives optical fibers as the potential nervous system of the Earth. Optical fibers are understood as continuous densely-packed sensing arrays, able of retrieving physical quantities from the environment of the fiber. Some of the most prominent distributed sensing implementations nowadays rely on performing interferometric measurements using the Rayleigh backscattered light, resorting to a technique called Phase-sensitive Optical Time-Domain Reflectometry (CP-ϕOTDR). A variant to this technique has been recently proposed in 2016, known as Chirped-Pulse Phase-Sensitive OTDR, which allowed to overcome most of the limitations of traditional ϕOTDR implementations while retaining a simple setup, yielding remarkably high sensitivities. In this thesis, we aim to optimize the stability and performance of chirped-pulse ϕOTDR systems over long-term measurements, and develop novel paradigm changing applications benefiting from the high sensitivity provided by the technique. We reach a mK-scale long-term stability in ϕOTDR systems, and perform highly sensitive strain, temperature, and refractive index measurements, demonstrating new photonic applications such as distributed bolometry, electro-optical reflectometry, or distributed underwater seismology. We discuss how these applications might be able of increasing the efficiency in the energy field, paving the way towards the development of self-diagnosable grids (smart-grids), and also of revolutionizing next-generation seismological networks, allowing to overcome some of the greatest limitations faced in modern seismology today.Distributed optical fiber sensing is currently a very predominant research field, which perceives optical fibers as the potential nervous system of the Earth. Optical fibers are understood as continuous densely-packed sensing arrays, able of retrieving physical quantities from the environment of the fiber. Some of the most prominent distributed sensing implementations nowadays rely on performing interferometric measurements using the Rayleigh backscattered light, resorting to a technique called Phase-sensitive Optical Time-Domain Reflectometry (φOTDR). A variant to this technique has been recently proposed in 2016, known as Chirped-Pulse Phase-Sensitive OTDR, which allowed to overcome most of the limitations of traditional φOTDR implementations while retaining a simple setup, yielding remarkably high sensitivities. In this thesis, we aim to optimize the stability and performance of chirped-pulse φOTDR systems over long-term measurements, and develop novel paradigm changing applications benefiting from the high sensitivity provided by the technique. We reach a mK-scale long-term stability in φOTDR systems, and perform highly sensitive strain, temperature and refractive index measurements, demonstrating new photonic applications such as distributed bolometry, electro-optical reflectometry, or distributed underwater seismology. We discuss how these applications might be able of increasing the efficiency in the energy field, paving the way towards the development of self-diagnosable grids (smart-grids), and also of revolutionizing nextgeneration seismological networks, allowing to overcome some of the greatest limitations faced in modern seismology today. We finally conclude and summarize the objectives achieved in this thesis, commenting on the potential of the novel applications shown, and proposing future lines of research based on the results

On the modelization of optical devices: from dielectric cavities to radiating structures

Premièrement, nous allons explorer la modélisation des cavités diélectriques bidimensionnelles. Plus spécifiquement, nous allons développer différentes méthodes de modélisation valides pour des cavités diélectriques à géométrie et profil d’indice de réfraction arbitraires. Ce degré de liberté supplémentaire pourra être utilisé dans le design de microcavités pour des applications spécifiques. Un formalisme de diffusion permettra de définir les modes caractéristiques de ce type de structure et d’en calculer les résonances. Une analyse numérique des équations résultantes montrera que les méthodes intégrales sont possiblement meilleures que les méthodes différentielles. Deuxièmement, nous discuterons de la modélisation de structures radiatives. Nous utiliserons les méthodes développées dans la section précédente pour modéliser les propriétés lasers des microcavités bidimensionnelles prédites par la théorie SALT. Nous aborderons aussi la modélisation de fibres-antennes RF, plus particulièrement les câbles coaxiaux à perte radiative, dans le but d’intégrer des fonctionnalités radio dans un textile de manière transparente à l’utilisateur.In this essay, we will develop different modelization techniques valid for bidimensional dielectric cavities having arbitrary geometries and refractive index profiles and provide a way to accurately compute the resonances of such structures. The refractive index thus becomes an additional design variable for dielectric cavities. A numerical analysis of of the underlying equations of the theory will reveal that perhaps it is best to forego differential equations in favour of integral ones for the scattering problem. In the second part, we will discuss the modelization of radiating structures. Using the formalism developed in the previous section, we will study the lasing properties of bidimensional cavities using the newly developed self-consistent ab initio laser theory (SALT). We will also touch on the modelization of the class of antenna known as leaky coa

M-sequenze based ultra-wideband radar and its application to crack detection in salt mines

Die vorliegende Dissertation beschreibt einen innovativen ultra-breitband (UWB)elektromagnetischen Sensor basierend auf einem Pseudo-Rauschverfahren.Der Sensor wurde für zerstörungsfreies Testen in zivilen Anwendungen entwickelt.Zerstörungsfreies Testen entwickelt sich zu einem immer wichtiger werdenden Bereich in Forschung und Entwicklung. Neben unzähligen weiteren Anwendungen und Technologien, besteht ein primäres Aufgabenfeld in der Überwachung und Untersuchung von Bauwerken und Baumaterialien durch berührungslose Messung aus der Ferne.Diese Arbeit konzentriert sich auf das Beispiel der Auflockerungszone im Salzgestein.Der Hintergrund und die Notwendigkeit, den Zustand der oberflächennahen Salzschichten in Salzminen kennen zu müssen, werden beleuchtet und die Messaufgabe anhand einfacher theoretischer Überlegungen beschrieben. Daraus werden die Anforderungen für geeignete UWB Sensoren abgeleitet. Die wichtigsten Eigenschaften sind eine sehr hohe Messband breite sowie eine sehr saubere Systemimpulsantwort frei von systematischen Gerätefehlern. Beide Eigenschaften sind notwendig, um die schwachen Rückstreuungen der Auflockerungen trotz der unvermeidlichen starken Oberflächenreflexion detektieren zu können.Da systematische Fehler bei UWB Geräten technisch nicht von vorne herein komplett vermeidbar sind, muss der Sensor eine Gerätekalibrierung erlauben, um solche Fehler möglichst gut zu unterdrücken.Aufgrund der genannten Anforderungen und den Nebenbedingungen der Messumgebung unter Tage, wurde aus den verschiedenen UWB-Technologien ein Prinzip ausgewählt, welches pseudozufällige Maximalfolgen als Anregungssignal benutzt. Das M-Sequenzkonzept dient als Ausgangpunkt für zahlreiche Weiterentwicklungen. Ein neues Sendemodul erweitert dabei die Messbandbreite auf 12~GHz. Die äquivalente Abtastrate wird um den Faktor vier auf 36~GHz erhöht, ohne den geringen Abtastjitter des ursprünglichen Konzepts zu vergrössern.Weiterhin wird die Umsetzung eines Zweitormesskopfes zur Erfassung von S-Parametern sowie einer automatische Kalibriereinheit beschrieben. Etablierte Kalibrierverfahren aus dem Bereich der Netzwerkanalyse werden kurz rekapituliert und die Adaption des 8-Term Verfahrens mit unbekanntem Transmissionsnormal für das M-Sequenzsystem beschrieben. Dabei werden Kennwerte vorgeschlagen, die dem Bediener unter Tage einfach erlauben, die Kalibrierqualität einzuschätzen und Hinweise auf mögliche Gerätefehler oder andere Probleme zu bekommen. Die Kalibriergenauigkeit des neuen Sensors im Labor wird mit der eines Netzwerkanalysators verglichen. Beide Geräte erreichen eine störungsfreie Dynamik von mehr als 60~dB in den Systemimpulsantworten für Reflexion und Transmission.Der neu entwickelte UWB Sensor wurde in zahlreichen Messungen in Salzminen in Deutschland getestet. Zwei Messbeispiele werden vorgestellt - ein sehr alter, kreisrunder Tunnel sowie ein ovaler Tunnelstumpf, welcher kurz vor den Messungen erst aufgefahren wurde. Messaufbauten und Datenverarbeitung werden beschrieben. Schließlich werden Schlussfolgerungen und Vorschläge für zukünftige Arbeiten mit dem neuen M-Sequenzsensor sowie der Messung von Auflockerungen im Salzgestein diskutiert.This dissertation describes an innovative ultra-wideband (UWB) electromagnetic sensor device based on a pseudo-noise principle developed in the context of non-destructive testing in civil engineering.Non-destructive testing is becoming a more and more important fieldfor researchers and engineers alike. Besides the vast field of possibleapplications and testing technologies, a prime and therefore typical topic is the inspection and monitoringof constructions and materials by means of contactless remote sensing techniques.This work focuses on one example the assessment of the disaggregation zone in salt rock tunnels.The background and relevance of knowing the state of salt rock layers near a tunnel's surface are explainedand simple theoretical considerations for requirements of suitable UWB sensor devices are shown. The most important sensor parameters are a very large measurement bandwidth and a very clean impulse response. The latterparameter translates into the mandatory application of calibration techniques to remove systematic errors of the sensor system itself. This enables detection of weak scattering responses from near-surface disaggregation despite the presence of a strong surface reflection.According to the mentioned requirements and other side conditions in salt mine environments an UWB sensor principlebased on pseudo-noise stimuli namely M-Sequences is selected as a starting point for system development. A newtransmitter frontend for extending the stimulus bandwidth up to 12~GHz is presented. Furthermore, a technique for increasing the (equivalent) sampling rate while keeping the stable and low-jitter sampling regime of the M-Sequencesapproach is introduced and its implementation is shown. Moreover, an automatic calibration unit for full two-port coaxial calibration of the new UWB sensor has been developed. Common calibration techniques from the area of vector network analysers are shortly reviewed and a reasonablealgorithm the 8-term method with an unknown line standard - is selected for the M-Sequences device. The 8-term method is defined in the frequency domain and is adapted for use with time domain devices. Some performance figures and comparisonwith calibration results from network analysers are discussed to show the effectiveness of the calibration.A spurious-free dynamic range of the time domain impulse responses in excess of 60~dB has been achieved for reflection as well as transmission measurements.The new UWB sensor was used in various real world measurements in different salt mines throughout Germany. Two measurementexamples are described and results from the disaggregation zone of a very old and a freshly cut tunnel will be presented. Measurement setup and data processing are discussed and finally some conclusions for future work on this topic are drawn

High-Density Digital Links: Optimization of Signal Integrity and Noise Performance of the High-Density Digital Links of the ATLAS-TRT Readout System

The Transition Radiation Tracker (TRT) is a sub detector of the particle detector ATLAS (A Toroidal LHC ApparatuS). About 420,000 detecting elements are distributed over 22 m3. They produce each second approximately 20 Tbit of data which has to be transferred from the front-end electronics inside the detector to the back-end electronics outside the detector for further processing. The task of this thesis is to guarantee the integrity of the signals and the electromagnetic compatibility inside the TRT as well as to the aggressive surroundings. The electromagnetic environment of particle detectors in high-energy physics adds special constraints to the high data rates and the high complexity: high sensibility of the detecting elements and their pre amplifiers, confined space, limited material budget, a radioactive environment, and high static magnetic fields. Thus many industrial standard measures have to be abandoned. Special design is essential to compensate this disadvantage