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In this thesis the feasibility of using superconductors to generate a magnetic field in an actuator is studied. The first objective of the thesis is to determine the achievable magnetic fields with commercially available superconductors. Second a superconducting actuator and its cryostat are designed. Finally the superconducting actuator is evaluated on its electromechanical, thermal and commercial feasibility.

In this Master thesis I report results on a route to find Majorana fermions in indium antimonide nanowires in contact with a superconductor. Theoretically Majorana fermions appear in one-dimensional nanowires with strong spin-orbit coupling, in proximity with a superconductor and an external magnetic field applied parallel to the nanowire. The nanowires are deposited by a deterministic method, in this way the external magnetic field is perfect aligned with the nanowires up to a few degrees. Results we observed are a possible magnetic field tunable pi-junction, measurements of an induced gap in the nanowire and a robust zero-bias peak that persist in both gate and magnetic field scans. This zero-bias peak can be split and recombine with varying the applied magnetic field and the local gate potential.

We demonstrate an increased quasiparticle recombination time in superconducting resonators on a SiNx membrane, compared to identical resonators on a SiNx/Si wafer. An interpretation is given using a thermal model of the membrane. Using an array of tunnel junctions to cool or heat the membrane, we show that the resonators on the membranes are extremely sensitive to small changes of the phonon temperature, which renders them excellent phonon thermometers with a noise level equivalent to 5μK/√Hz. The experimental set-up is in principle an ideal platform to study the interplay of quasiparticles and phonon populations in superconductors.

We describe the optimization of transition edge superconducting (TES) detectors for use in a far-infrared (FIR) Fourier transform spectrometer (FTS) mounted on a cryogenically cooled space-borne telescope (e.g. SPICA). The required noise equivalent power (NEP) of the detectors is approximately 10−19 W/ √Hz in order to be lower than the photon noise from astrophysical sources in octave wide bands in the FIR. The detector time constants must be less than 10 ms in order to allow fast scanning of the FTS mechanism. The detectors consist of superconducting thermometers suspended on thin legs of thermally isolating silicon nitride and operate at a temperature of approximately 100 mK. We present the design of the detectors, a proposed focal plane layout and optical coupling scheme and measurements of thermal conductance and time constant for low NEP prototype TES bolometers.

We have studied the sensitivity of a superconducting NbN hot electron bolometer mixer integrated with a spiral antenna at 4.3 THz. Using hot/cold blackbody loads and a beam splitter all in vacuum, we measured a double sideband receiver noise temperature of 1300 K at the optimum local oscillator (LO) power of 330 nW, which is about 12 times the quantum noise (hν/2kB). Our result indicates that there is no sign of degradation of the mixing process at the superterahertz frequencies. Moreover, a measurement method is introduced which allows us for an accurate determination of the sensitivity despite LO power fluctuations.

The ALMA Band 9 receiver cartridge (600-720 GHz) based on Dual Sideband (DSB) superconductor-insulatorsuperconductor (SIS) mixer is currently in full production. In the case of spectral line observations, the integration time to reach a certain signal-to-noise level can be reduced by about a factor of two by rejecting an unused sideband. The goal is to upgrade the current ALMA band 9 cartridge to a full dual-polarization sideband separating (2SB) capability, with minimal-cost upgrade path. A new compact and modular sideband separating mixer was designed, and a prototype manufactured. The individual SIS mixer devices in the 2SB block are implemented as conventional Band 9 DSB mixers, so that existing devices can be reused and tested individually. Any ALMA DSB developments contribute to the 2SB upgrade. The first experimental results demonstrate noise temperature from 300K to 500K over 80% of the band, which will be improved to fit the ALMA requirements. Nevertheless, the frequency response for 2SB is the same as for DSB, showing that the RF design is still valid, even with different SIS mixer devices. The quality of the RF and IF design is confirmed by a sideband rejection ratio of about 15 dB, which is within the ALMA spec (>10dB ).

The demand for electric power keeps on growing and electrical power networks are becoming more interconnected. This is a trend in many countries of the world that is caused by increased customer requirements and advanced technological improvements. In order to meet the ever-increasing energy demand, the integration of new power sources in the grid is necessary. This is a big challenge due to bottlenecks such as transport capacity, voltage fluctuations, fault levels and reactive power. The great challenge lies in the design of a network, with a smooth voltage profile and limited short circuit currents. The smart-grid vision and the newest High Temperature Superconducting (HTS) cable technologies, can offer solutions for these issues. HTS cables will have a smart behavior, because they have an improved non-linear voltage-current characteristic. This innovative characteristic is caused by the non-linear resistance of the HTS cable. During normal operation the cable resistance is very low, resulting in low energy losses and smoother voltage profile. While the non-linear resistance increases very fast during short circuits, a significant reduction is caused in the fault currents. This physical Fault Current Limiting (FCL) cable property is analyzed for the connection of a power plant with a 150 kV FCL HTS cable. An EMTP-ATP draw model is developed by using MODELS language based on the R ~ It characteristics of FCL HTS cable. Short-circuit current analysis are carried out for this model, with and without the FCL HTS cable. When a fault occurs and the results are compared, the FCL HTS cable is capable of limiting the fault current. For this model the generator terminal voltage and the Transient Recovery Voltage (TRV) have been analyzed. When a three-phase to ground fault occurs, the generator terminal voltage stays within the specified limits. The results of the TRV analysis are compared with the standard value that is allowed by the IEC.

The electromagnetic waves are considered in this article as the mediators of interaction in the Meissner Effect or the diamagnetic property of the superconductors. During the cooling of a superconductor electromagnetic waves may be released when the electrons occupy lower states of the energy. These electromagnetic waves may combine in circularly, elliptically and spherically rotating ways, being called in this article the rounded electromagnetic fields. The application of the Lorentz transformation of the Special Theory of Relativity to the magnetic vectors of the mediating electromagnetic fields implies the magnetic orthogoniopedic effect inside the bulk of a superconductor in the Meissner Effect.

Integrating NbTiN-based microstrip tuning circuits with traditional Nb superconductor-insulator-superconductor (SIS) junctions enables the low-noise operation regime of SIS mixers to be extended from below 0.7 to 1.15 THz. In particular, mixers incorporating a NbTiN/SiO2/NbTiN microstrip tuning circuit offer low-noise performance below 0.8–0.85 THz, although their sensitivities drop significantly at higher frequencies. Furthermore, a microstrip geometry in which NbTiN is used as the ground plane material only (NbTiN/SiO2/Al) yields significant improvements in the sensitivities of SIS mixers operating up to 1.15 THz, with an upper operating frequency that depends upon the quality of the NbTiN layer, and thus its deposition process. Films deposited at room temperature have Tc = 14.4 K and ρn,20 K ∼ 60 μΩ cm, and offer low-noise performance up to 1 THz, whereas films deposited at 400 °C have Tc = 16 K and ρn,20 K ∼ 110 μΩ cm, and offer low-noise performance up to 1.15 THz. Taken together, these results demonstrate that the high-frequency surface resistance of a NbTiN layer depends upon the film’s structural properties. Most significantly, the drop in performance that is seen at F>1 THz in mixers incorporating NbTiN ground planes deposited at room temperature is attributed to nonhomogeneities in the structural and electrical properties of these films, as is the poor performance of mixers that incorporate NbTiN wiring layers at F>0.85 THz. The development of these NbTiN-based microstrip tuning circuits will enable the production of low-noise SIS mixers for the 0.8–0.96- and 0.96–1.12-THz frequency bands of the Heterodyne Instrument for the Far Infrared on board the European Space Agency’s Herschel Space Observatory.

Carbon Nanotubes are molecules with exceptional physical properties that are most useful for applications in the growing field of nanotechnology. In addition, because of its special electrical properties, they are extremely useful for experiments on the fundamental properties of one-dimensional electronic systems. This thesis describes a series of experiments and a short numerical study aimed at a further understanding of the low-temperature electrical transport of single-walled carbon nanotubes. In this work we perform the first experimental study on the effect of quantum interference in single-wall nanotubes in the presence of disorder, leading to the observation of a weak localization effect and conductance fluctuations. Shifting the focus to systems with superconducting or ferromagnetic contacts, we first propose a phenomenological model to describe the experimental results from a former study with superconducting contacts. We also contact single-wall nanotubes with the large-gap superconductor NbTiN to study the rich interplay between Coulomb blockade, level quantization and superconductivity. And finally, the experimental study of nanotubes with highly transparent ferromagnetic contacts shows that the spin-dependent magnetoresistance is due to quantum interference.