The electromagnetic response of infinitely long, thin wires over a flat earth is presented for two different applications: the shielding properties of an ensemble of parallel wires excited by a plane wave and the electromagnetic coupling of two perpendicular wires excited by a dipole. The shielding study begins with the formulation of the boundary value problem for N wires over a lossy half space. A suitable axial impedance operator is applied to obtain a system of equations whose unknowns are the currents flowing on each wire. Once the currents are determined, the aggregate field produced by the ensemble can be computed by summing N Fourier type integrals. For the specialized case of the infinite planar grid, Floquet's Theorem and Poisson's Summation Formula are invoked, transforming the linear system of equations into a closed form expression for the current flowing on each wire. We show that the electromagnetic response of the planar grid of finite extent and the grid of infinite extent are similar. For non-planar configurations, such as the semi-circular shell, shielding values of 60 dB are possible when the structure is of non-resonant dimensions; otherwise, the performance can degrade to 20 dB. In the case of the crossed wire configuration, the starting point is the development of the integral equations that govern the coupling between wires and the source; the unknowns are the spectral currents flowing in each wire. The equations are given in terms of generalized impedance functions for the situation where the wires are over a stratified earth. However, for the numerical work, only the case where the wires are in an unbounded, homogeneous medium is considered. Two numerical methods, with overlapping regions of validity, are applied: the method of moments and the method of multiple scatterers. By using the method of moments, we can obtain a matrix equation that will determine the spectral currents for any wire spacing. The multiple scatterer method leads to a more convenient matrix series solution and shows that the coupling strength is proportional to 1/d², where d is the wire separation, plus higher order inverse terms.

Thesis (M.S.)--California Polytechnic State University, 2009. / Mode of access: Internet. Title from PDF title page; viewed on July 10, 2009. Major professor: Dr. Eric Mehiel. "Presented to the faculty of California Polytechnic State University at San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Aerospace Engineering with specialization in Space Systems Engineering." "April 2009." Includes bibliographical references (p. 48).

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 111-113).

Particle accelerators produce beams of high-energy particles, which are used for both fundamental and applied scientific research and are critical to the development of accelerator driven sub-critical reactor systems. An effective magnetic shield is very important to achieve higher quality factor (Qo) of the cryomodule of a particle accelerator. The allowed value of field inside the cavity due to all external fields (particularly the Earth’s magnetic field) is ~15 mG or less. The goal of this PhD dissertation is to comprehensively study the magnetic properties of commonly used magnetic shielding materials at both cryogenic and room temperatures. This knowledge can be used for the enhanced design of magnetic shields of cryomodes (CM) in particle accelerators. To this end, we first studied the temperature dependent magnetization behavior (M-H curves) of Amumetal and A4K under different annealing and deformation conditions. This characterized the effect of stress or deformation induced during the manufacturing processes and subsequent restoration of high permeability with appropriate heat treatment. Next, an energy based stochastic model for temperature dependent anhysteretic magnetization behavior of ferromagnetic materials was proposed and benchmarked against experimental data. We show that this model is able to simulate and explain the magnetic behavior of as rolled, deformed and annealed amumetal and A4K over a large range of temperatures. The experimental results for permeability are then used in a finite element model (FEM) in COMSOL to evaluate the shielding effectiveness of multiple shield designs at room temperature as well as cryogenic temperature. This work could serve as a guideline for future design, development and fabrication of magnetic shields of CMs.

No description available.

The neutron Electric Dipole Moment Experiment at the Spallation Neutron Source requires an overall magnetic shielding factor of order 105 to attenuate external background magnetic fields. At present, the shielding design includes an external (room-temperature) multi-layer μ-metal magnetic shield, a cryogenic (4 Kelvin) Pb superconducting shield, and a cryogenic (4 Kelvin) ferromagnetic shield composed of Metglas ribbon. This research determined how to construct a Metglas shield using minimal material that produced axial and transverse shielding factors of ~267 and ~1500. In addition, the μ-metal and Metglas shields were modeled using finite element analysis. The FEA model includes external coils and their effect on the residual magnetic fields. This study will help with the design of the shielding.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This work discusses the design of a 3-axis Geomagnetometer SQUID System (GSS), in which HTS SQUIDs are used unshielded. The initial GSS installed at SANSA was fully operable, however the LN2 evaporation rate and SQUID orientation required improving. Magnetic shields were also developed in case the SQUIDs would not operate unshielded and to test the system noise with geomagnetic variations removed. To enable removing the double layer shield from the probes while the SQUIDs remain submerged in LN2, the shield was designed to disassemble. The shields proved to be effective, however due to icing the shields could not be removed without removing the SQUIDs from the LN2. / AFRIKAANSE OPSOMMING: Hierdie werk bespreek die ontwerp van 'n 3-as Geomagnetometer SQUID Sisteem (GSS), waarin HTS SQUIDs sonder magnetiese skilde aangedryf word. Die aanvanklike GSS geïnstalleer by SANSA was ten volle binnewerking, maar die LN2 verdamping en SQUID oriëntasie benodig verbetering. Magnetiese skilde was ook ontwikkel vir die geval dat die SQUIDs nie sonder skilde wou werk nie en om die ruis te toets na geomagnetiese variasies verwyder is. Die dubbele laag skild was ontwerp om uitmekaar gehaal te word terwyl die SQUIDs binne die LN2 bly. Die skild was doeltreffend, maar ys het verhoed dat die skild verwyder kon word vanaf die LN2 sonder om die SQUIDs ook te verwyder.

Les propulseurs de Hall sont l’une des techniques de propulsion fusée par plasma les plus utilisés. Ils possèdent une impulsion spécifique moyenne et un haut rapport poussé sur puissance qui les rend idéal pour une grande partie des applications commerciales et scientifiques. Une de leurs limitations principales est l’érosion des parois du propulseur par le plasma qui réduit leur durée de vie. La topologie dite “d’écrantage magnétique” est une solution proposée pour prolonger cette durée de vie. Elle est ici appliquée à un petit propulseur de Hall de 200W. Dans cette thèse les règles de mise à l’échelle pour les propulseurs de Hall de la gamme de 100 à 200W sont testées expérimentalement. Un propulseur écranté de 200W est comparé avec un propulseur standard similaire. Le comportement des ions dans ces deux moteurs est extrêmement différent. Des mesures de performance ont été réalisées avec des parois en BN-SiO2 et graphite. Le courant de décharge augmente de 25% avec le graphite dans le propulseur non-écranté. Le résultat et un rendement maximum de 38% avec le nitrure de bore mais de seulement 31% pour le graphite. Le propulseur écranté quant à lui n’atteint que 25% de rendement quel que soit le matériau.Cette baisse de performance dans les petits moteurs écrantés peut être attribuée à un mauvais rendement d’utilisation de l’ergol. Analyses des résultats expérimentaux ainsi que la conduite de simulations suggèrent que cela est dû au fait que la zone d’ionisation ne couvre pas l’ensemble du canal de décharge. Un nouveau design pour un petit propulseur de Hall écranté est proposé. / Hall thrusters are one of the most used rocket electric propulsion technology. They combine moderate specific impulse with high thrust to power ratio which makes them ideal for a wide range of practical commercial and scientific applications. One of their limitations is the erosion of the thruster walls which reduces their lifespan.The magnetic shielding topology is a proposed solution to prolong the lifespan. It is implemented on a small200W Hall thruster.In this thesis the scaling of classical unshielded Hall thrusters down to 200 and 100W is discussed. A 200W low power magnetically shielded Hall thruster is compared with an identically sized unshielded one. The ion behavior inside the thruster is measured and significant differences are found across the discharge channel.Both thrusters are tested with classical BN-SiO2 and graphite walls. The magnetically shielded thruster is not sensitive to the material change while the discharge current increase by 25% in the unshielded one. The result is a maximum efficiency of 38% for boron nitride in the unshielded thruster but only 31% with graphite.The shielded thruster achieves a significantly lower efficiency with only 25% efficiency with both materials.Analysis of the experimental results as well as simulations of the thrusters reveal that the performance difference is mostly caused by low propellant utilization. This low propellant utilization comes from the fact that the ionization region doesn’t cover all of the discharge channel. A new magnetically shielded thruster is designed to solve this issue.

Abstract The subjects of this thesis are the dynamics of liquid crystals in external electric and magnetic fields as well as the magnetic properties of small molecules, both studied by liquid crystal nuclear magnetic resonance (LC NMR) spectroscopy. Director dynamics of a liquid crystal 5CB in external magnetic and electric fields was studied by deuterium NMR and spectral simulations. A new theory was developed to explain the peculiar oscillations observed in the experimental spectra collected during fast director rotation. A spectral simulation program based on this new theory was developed and the outcome of the simulations was compared with the experimental results to verify the tenability of the theory. In the studies on the properties of small solute molecules, LC NMR was utilised to obtain information about anisotropic nuclear magnetic interaction tensors. The nuclear magnetic shielding tensor was studied in methyl halides, the spin-spin coupling tensor in methyl mercury halides and the quadrupolar coupling tensor in deuterated benzenes. The effects of small-amplitude molecular motions and solvent interactions on the obtained parameters were considered in each case. Finally, the experimental results were compared to the corresponding computational NMR parameters calculated in parallel with the experimental work.

La propulsion électrique est à un tournant de son histoire. La récente mise en oeuvre de satellites de télécommunication "tout-électrique" se traduit par l’ouverture d’un nouveau marché, et par une évolution des besoins opérationnels. L’identification de ces nouvelles missions nécessite l’amélioration des performances de nos moteurs. La première partie de ces travaux rapporte l’utilisation d’un outil de spectroscopie laser destiné à caractériser la distribution en vitesse des ions. Les différentes méthodes de calcul du champ électrique dans les propulseurs de Hall ont été exposées. Deux instabilités ioniques ont été observées et analysées. Les sources d’erreurs liées aux mesures par sondes électrostatiques ont été analysées, et un exemple de sonde plane étudié. Une analyse paramétrique de l’influence des paramètres de champ magnétique sur les performances des propulseurs de Hall a été conduite. Le concept de moteur "sans parois" est présenté. L’identification de ce concept constitue une avancée porteuse de promesses pour l’avenir de la propulsion électrique. / Electric propulsion is facing new challenges. Recently, the launch of "all-electric" satellites has marked the debut of a new era. Going all-electric now appears as an interesting alternative to conventional systems for telecom operators. A laser spectroscopy technique was used during this research to investigate the ion velocity distribution dynamics. The different methods for determining the electric field in Hall thrusters were exposed. Two unstable ion regimes were identified and examined. Measurement uncertainties using electrostatic probes were assessed. Planar probed have been designed and tested. A thorough investigation of the influence of the magnetic field parameters on the performance of Hall thrusters was performed. The wall-less Hall thruster design was presented, and preliminary experiments have revealed its interest for the electric propulsion community.