<p>The Large Hadron Collider (LHC) is presently under construction at CERN. The LHC is a circular accelerator that stores proton beams and accelerates them to a 7 TeV beam energy for high energy physics research. The required bending and focusing/defocusing fields are achieved with superconducting magnets.</p><p>Such a superconducting magnet-based accelerator can be controlled only when the field errors of production and installation of all magnetic elements are known to the required accuracy. The ideal way to compensate the field errors is to have direct diagnostics on the beam. For the LHC, however, a system solely based on beam feedback may be too demanding. The present baseline for the LHC control system hence requires an accurate forecast of the magnetic field and the multipole field errors to reduce the burden on the beam-based feedback. The field model is the core of this magnetic prediction system, also known as \emph{the Field Description for the LHC} (FIDEL). The model will provide the forecast of the magnetic field at a given time, magnet operating current, magnet ramp rate, magnet temperature, and magnet powering history. The model is based on the identification and physical decomposition of the effects that contribute to the total field in the magnet aperture of the LHC dipoles.</p><p>This thesis presents the tool that was constructed to ease the detection, identification and finally correction of errors in the raw data from the series measurements of the main dipoles of the LHC. The results after cleaning all measurement data for the over 240 dipoles measured at cold, using this tool, is also presented.</p><p>Another aspect of the Thesis is the presentation of a procedure devised to extract the model parameters for the main dipole magnets of the LHC by using the cleaned data. The procedure and the model are verified and validated by application to the magnets of the 7-8 sector of the LHC.</p>

This thesis studies the intrinsic disorder effects and the transport and magnetic properties of ring-shaped epitaxial thin films and superconducting tunnel junctions (STJs) of the high temperature superconductor YBa$_2$Cu$_3$O$_{7-delta}$. We used an unconventional contactless technique that allows us to directly measure the persistent current of superconducting rings. In order to study the disorder effects on the persistent current, we slowly increased oxygen vacancies in YBa$_2$Cu$_3$O$_{7-delta}$ by changing $delta$ from 0.03 to 0.55 in steps of $sim$0.021. Monitoring the corresponding changes in the temperature dependence of the persistent current revealed an anomaly in its flow within a certain range of disorder. We found that this anomaly is directly related to the occurrence of a spinodal decomposition of oxygen vacancies in YBCO, which we explain as a competition between two coexisting phases, oxygen rich and oxygen deficient. The analysis of the time dependence of the persistent current revealed that increasing oxygen vacancies transforms the vortex structure from quasi-lattice into a glass and subsequently into a pinned liquid phase. Our results also exhibited the first evidence of self-organization of the vortex structure with increasing disorder. We also performed the first direct measurement of the temperature dependence of the $c$-axis persistent current ($J_c$) that is purely due to tunnelling Cooper-pairs through intrinsic Josephson junctions (IJJs) of YBCO. This is made possible by incorporating IJJs of YBCO into ring-shaped films. Then, we studied the temperature dependence of the persistent current of YBCO nanowires embedded in SrTiO$_3$-barrier integrated between two semi-ring-shaped YBCO thin films and systematically varied the nanowires length. Our observations revealed that $J_c$ has two different temperature dependences: a GL-dependence ($J_c propto (T_c - T)^{3/2}$) at low temperatures which we found the same in all studied samples, and another power law dependence ($J_c propto (T_c - T)^{alpha > 3/2}$) at high temperatures which turned out to depend on the length of the nanowires. We attribute the cross-over between these two temperature dependences to the depinning and the dissipative motion of vortices. These experimental approaches and findings not only provide new information, but more importantly open new avenues of investigating the transport and magnetic properties of superconducting films, junctions, and nanowires.

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The quantum properties of electromagnetic radiation at single photon level promise to offer what are classically inaccessible. Single photon sources and detectors are therefore on demand for exploiting these properties in practical applications, including but not limited to quantum information processing and communication. In this thesis, I advance Superconducting Nanowire Single Photon Detectors (SNSPD) both in terms of models describing their operation, and their performance. I report on characterization, semi-empirical modeling, quantum-optical modeling and detector tomography. The results provide more accurate methods and formulations to characterize and mathematically describe the detectors, valuable findings from both application and device points of views. I also introduce the concept of Gated SNSPDs, show how to implement and how to characterize them. Through series of theoretical and experimental investigations, I show performance advantages of Gated SNSPDs in terms of dead time and dark count rate, important figures for many applications like quantum key distribution. The ultimate limitations of gated operation are also explored by physical modeling and simulation steps.

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Superconducting microelectronics (SME) technology has the potential of realizing very high speed digital receivers capable of performing direct digitization of radio frequency signals with very low power consumption. The SME receiver is implemented on a single chip using Niobium based low temperature superconductive (LTS) Josephson Junction (JJ) technology by HYPRES. Analogue RF filters are still required at the receiver front end and are key components of the overall superconductor digital receiver. SME receivers usually require two types of RF filters; a wideband bandpass filter and a bandstop filter (a notch filter). The notch filter is required to eliminate interference and unwanted signals in the passband. In this thesis, design of highly miniaturized lumped element wideband and bandstop filters is investigated and some challenges are addressed. The filters are fabricated by the HYPRES process and therefore can be integrated with the SME receiver on the same chip. In a wideband filter, the coupling between the adjacent resonators is high. Achieving such a strong coupling is one of the challenges of designing wideband filters. The wideband filters realized with distributed elements usually suffer from very low spurious frequency. As the bandwidth of the filter becomes wider, the spurious peak of the second harmonic gets closer to the passband of the filter. In the first part of this work, the possibility of realizing lumped element superconducting bandpass filters (BPF) with a relative bandwidth of 80% is investigated. In the second part of the thesis, design and realization of lumped element superconducting bandstop filters (BSF) is discussed. The challenge for designing a bandstop filter is providing a good match over a wide frequency range. So narrowband inverters cannot be used. Instead, usually λ/4 matched transmission lines provide 90° phase shift between the resonators of a notch filter. The possibility of replacing the long transmission line with other means or eliminating the inverters and using both shunt and series resonators are investigated. Having both series and shunt resonators introduces some new challenges that are addressed in the thesis and discussed thoroughly. A tunable notch resonator is presented. The tunability is provided by a superconducting MEMS varactor that is realized in our group by doing some post processing on the device fabricated by HYPRES. The tunability range of the device at cryogenic temperatures is investigated. A 3-pole tunable BSF is also designed that uses the same tunable resonators. The tunability of the filter is investigated through simulation.

Fabrication of nanoscale Josephson junctions and Superconducting Quantum Interference Devices (SQUID) is very promising but challenging topic in the superconducting electronics and device technology. In order to achieve best sensitivity of SQUIDs and to reproduce them easily with a straightforward method, new fabrication techniques for realization of nanoSQUIDs needs to be investigated. This study concentrates on investigation of new fabrication methodology for manufacturing nanoSQUIDs with High Temperature Bi-Crystal Grain Boundary Josephson Junctions fabricated onto SrTiO3 bi-crystal substrates using YBa2Cu3O7-δ (YBCO) thin-films. In this process nanoscale patterning of YBCO was realized by using electron beam patterning and physical dry etching of YBCO thin films on STO substrates. YBCO thin films were deposited using RF magnetron sputtering technique in the mixture of Ar and O2 gases and followed by annealing at high temperatures in O2 atmosphere. Structural characterization of YBCO thin films was done by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). Superconducting properties of thin films was characterized by AC magnetic susceptibility measurements. Nanoscale structures on YBCO thin films were fabricated by one E-Beam Lithography (EBL) step followed by Reactive Ion Etching (RIE) and physical dry etching. First SiO2 thin film were deposited on YBCO by RF magnetron sputtering and it was patterned by EBL using Polystyrene (PS) as resist material and RIE. Then SiO2 was used as an etch mask for physical dry etching of YBCO and nanoscale structures on YBCO were formed.