published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Cette thèse traite de la compensation magnétique de pesanteur. Tout d’abord, des expériences de lévitation magnétique de fluides sont interprétées à l’aide d’un potentiel magnéto-gravitationnel SL. Puis, l’utilisation d’une méthode générale d’analyse de la force magnétique grâce aux harmoniques du champ magnétique est développée. Elle souligne l’importance et le rôle de chacun des trois premiers harmoniques du champ magnétique sur les configurations de forces résultantes inhérentes à la compensation magnétique de pesanteur. En géométrie cylindrique (invariante par translation) diverses combinaisons de forces d’origines magnétique, gravitationnelle et centrifuge offrent des perspectives nouvelles pour la lévitation magnétique. Une combinaison judicieuse des forces magnétiques et centrifuges permet de compenser exactement la pesanteur sur des matériaux diamagnétiques. En géométrie axisymétrique (invariante par rotation), le dimensionnement de stations de lévitation d’oxygène, techniquement réalisables (NbTi@4,2K), est présenté. Ces stations permettent de léviter des volumes d’oxygène supérieurs à 1 litre avec des inhomogénéités inférieures à 1%. La constitution de ces stations rend possible les variations spatiales et temporelles des configurations d’accélérations résultantes. Enfin, la compensation magnétique dynamique de gravité, à l’aide d’une station de lévitation réelle, est étudiée afin de simuler des phases d’accélération ou de décélération d’engins spatiaux / The thesis deals with magnetic gravity compensation. First of all magnetic levitation experiments are explained with the help of a magneto-gravitational potential SL. Next, a general analysis method of the magnetic force is developed which employs magnetic field harmonics. The method underlines both the significance and role of the first three magnetic field harmonics on the resulting forces inherent in magnetic gravity compensation. In cylindrical geometry – with translational invariance – various combination of magnetic, gravitational and centrifugal forces open new possibilities for the magnetic levitation. A suitable combination of both magnetic and centrifugal forces allows exactly compensating gravity on diamagnetic materials. In axisymmetric geometry – with rotational invariance – designs of feasible oxygen magnetic levitation stations are introduced (NbTi@4,2K). Levitation of oxygen volumes more than one litre with inhomogeneities less than 1% can be accomplished within these magnetic levitation facilities. The constitution of the stations makes possible both spatial and temporal variations of the resulting acceleration configurations. At last the dynamic magnetic compensation of gravity with a real coil system is studied so as to simulate both acceleration and deceleration of spaceships

The Swiss Free Electron Laser (SwissFEL) at the Paul Scherrer Institute is a national prestige project that will enable ground breaking new x-ray scattering experiments in areas such as biology, chemistry and physics. A plannedactivity is to generate possibility for x-ray diffraction under high pulsed magnetic fields to explore quantum mattermaterials. In fact, an entire beam line (CristallinaQ), dedicated to extreme sample environment (vacuum, electro-magnetic field, low temperature).This Master’s thesis project concerns the development of a magnet system for pulsed magnetic fields to be synchronised with the free electron laser pulses. The system is based on small-sized coils. This makes the systemtransportable and avoids the huge financial challenges and power requirements of the magnets at pulsed fields laboratories at Toulouse, Dresden or Tallahassee. Ultimately the magnet shall provide large pulsed fields of more than 30 T under conditions very similar to space, i.e. vacuum, low-temperature.The thesis presents the development of a complete coil manufacture and testing setup including a capacitor bank topower the magnet. With planned upgrades of the equipment, the coil manufacturing process is reaching reproduceable levels. I produce a first iteration of magnet coils. They follow a classical copper conductor design reinforcedwith an epoxy-Zylon matrix. During testing we produced 15 Tesla fields without degradation of the coils. At lastI analyse the observations from the tests and propose improvements and future steps for the further developmentof the magnet.

This thesis describes a portfolio of work aimed at the high field applications of superconductors and can be split into four main topics: The thermal stability of technical superconductors. This section investigates the effects of thermal perturbations on technical superconducting wire used in MRI scanner construction. The ultimate aim of this section is to predict how the architecture of the wire may affect its thermal stability. To this end a detailed finite element analysis model was constructed, verified by detailed experimental data, which could then be used to quickly and easily vary the wire’s parameters. Design of a high field pulsed electromagnetic coil for flux trapping in superconductors. This section details the design, construction and testing of a novel pulsed high field magnet. The design uses finite element analysis to predict the electromagnetic, thermal and structural properties of the coil. Explosive testing of high tensile fibres used in the construction of the high field coil. This section describes the refinement and use of a novel method for testing the mechanical properties of high tensile fibres in cylindrical geometries by using highly pressurized copper vessels. Pulsed field magnetization of bulk high temperature superconductors. This section discusses the process of magnetizing bulks of high temperature superconductors by using pulsed magnetic fields. It investigates how the trapped field varies with the magnitude and rise-time of the magnetizing field, sample temperature and time after magnetization.