Rayleigh Approximation to Ground State of the Bose and Coulomb Glasses

Glasses are rigid systems in which competing interactions prevent simultaneous minimization of local energies. This leads to frustration and highly degenerate ground states the nature and properties of which are still far from being thoroughly understood. We report an analytical approach based on the method of functional equations that allows us to construct the Rayleigh approximation to the ground state of a two-dimensional (2D) random Coulomb system with logarithmic interactions. We realize a model for 2D Coulomb glass as a cylindrical type II superconductor containing randomly located columnar defects (CD) which trap superconducting vortices induced by applied magnetic field. Our findings break ground for analytical studies of glassy systems, marking an important step towards understanding their properties

Development of HTS trapped field magnet using 2G HTS coated conductors

Compact High-Temperature Superconducting (HTS) trapped field magnets stand at the frontier of breakthroughs for advanced industrial equipment, medical devices, and transportation electrification, offering capabilities that conventional permanent magnets and electromagnets cannot achieve. While superconductors capitalize on zero resistance to uphold high currents, thus generating substantial fields, traditional HTS bulks and stacks have been limited by constraints such as geometry size and mechanical robustness. As second-generation (2G) commercial HTS coated conductors advance, there's a growing emphasis on utilizing these tapes to attain expansive and stable trapped field profiles. This thesis explores the innovative magnetization mechanisms and design optimizations of HTS trapped field magnets fabricated with 2G HTS tapes through a comprehensive analysis of HTS-stacked ring magnets, hybrid HTS-stacked ring design, their mechanical stress responses, and trapped field closed-loop HTS coil under field cooling magnetization. The research primarily investigated a novel hybrid HTS trapped field magnet, integrating HTS-stacked ring magnets with HTS bulks to surpass traditional size limitations and achieve a significant trapped field of 7.35 T. It further predicted their capability to generate a trapped field exceeding the applied field due to unique induced current distributions and flux redistribution. Additionally, the study addressed the mechanical challenges posed by Lorentz forces during magnetization, presenting 3D numerical models to analyze stress and strain in HTS-stacked ring magnets. A 90 % stress reduction was seen by proper impregnation and fixation methods. Lastly, a novel closed-loop HTS coil approach was introduced, achieving a compact high-field superconducting magnet that trapped a central field 4.59 T which was higher than the 4.5 T applied field, showcasing potential for diverse high-field applications. Above the inner edge of the HTS coil, the trapped field exceeded the applied field by 1.5 T. This thesis combines experimental findings and numerical modelling to advance the understanding of HTS magnetization processes, offering insights into designing more efficient and durable compact and portable HTS magnets for applications in nuclear magnetic resonance, Maglev transportation, and HTS machineryCompact High-Temperature Superconducting (HTS) trapped field magnets stand at the frontier of breakthroughs for advanced industrial equipment, medical devices, and transportation electrification, offering capabilities that conventional permanent magnets and electromagnets cannot achieve. While superconductors capitalize on zero resistance to uphold high currents, thus generating substantial fields, traditional HTS bulks and stacks have been limited by constraints such as geometry size and mechanical robustness. As second-generation (2G) commercial HTS coated conductors advance, there's a growing emphasis on utilizing these tapes to attain expansive and stable trapped field profiles. This thesis explores the innovative magnetization mechanisms and design optimizations of HTS trapped field magnets fabricated with 2G HTS tapes through a comprehensive analysis of HTS-stacked ring magnets, hybrid HTS-stacked ring design, their mechanical stress responses, and trapped field closed-loop HTS coil under field cooling magnetization. The research primarily investigated a novel hybrid HTS trapped field magnet, integrating HTS-stacked ring magnets with HTS bulks to surpass traditional size limitations and achieve a significant trapped field of 7.35 T. It further predicted their capability to generate a trapped field exceeding the applied field due to unique induced current distributions and flux redistribution. Additionally, the study addressed the mechanical challenges posed by Lorentz forces during magnetization, presenting 3D numerical models to analyze stress and strain in HTS-stacked ring magnets. A 90 % stress reduction was seen by proper impregnation and fixation methods. Lastly, a novel closed-loop HTS coil approach was introduced, achieving a compact high-field superconducting magnet that trapped a central field 4.59 T which was higher than the 4.5 T applied field, showcasing potential for diverse high-field applications. Above the inner edge of the HTS coil, the trapped field exceeded the applied field by 1.5 T. This thesis combines experimental findings and numerical modelling to advance the understanding of HTS magnetization processes, offering insights into designing more efficient and durable compact and portable HTS magnets for applications in nuclear magnetic resonance, Maglev transportation, and HTS machiner

High-temperature superconducting ring magnet

Many electrical engineering applications such as motors and generators use permanent magnets which approximately account for 45% of their electricity consumption. The conventional magnets in use have a maximum field of around 1.5-2 T. High performance superconducting materials such as REBCO have facilitated the development of superconducting magnets. Superconducting bulk magnets and stacks of tapes have already demonstrated the extraordinary potential to trap magnetic fields of very high order with very compact sizes. This has significantly increased the efficiency of rotating machines and improved power/torque density, while having low synchronous reactance with large overloading capacity, high transient stability with low noise and harmonic content with the additional cost of cooling. This thesis focuses on a new type of superconducting magnet which uses superconducting tape as the field source. The most significant limiting factor for superconducting magnets is their size.;This new superconducting magnet has made possible the development of HTS magnets with flexible sizes by splitting the 2G HTS tapes to form the persistent current rings. By stacking HTS closed loop rings into a compact magnet, our HTS ring magnet has been proven to generate a trapped magnetic field higher than 5 T. The main advantage of the new magnet compared to existing trapped field HTS magnets is that the magnetic field lies parallel to the ab plane of the HTS, leading to higher critical currents in the same magnetic field. This thesis reports our key findings so far. Two different stacking configuration magnet samples were tested using the field cooling magnetization at 25 K and 4.2 K, with magnet diameter 90 mm and 150 mm, respectively. Over 4.6 T of the trapped field has been reported by using Super Power tapes with a field cooling process at 25 K, which is the highest field trapped in the ring magnets for first configuration. A new stacking design was proposed to improve magnetic field distribution within the magnet and has the potential to trap more magnetic field with the estimated trap field of 9.4 T at 4.2 K. A three dimensional model was developed to simulate the performance of the ring magnets, and good agreements between experiment and simulation have been achieved. The new HTS permanent magnet with improved field homogenisation and large diameter is promising for medical imaging applications, as well as propulsion applications.Many electrical engineering applications such as motors and generators use permanent magnets which approximately account for 45% of their electricity consumption. The conventional magnets in use have a maximum field of around 1.5-2 T. High performance superconducting materials such as REBCO have facilitated the development of superconducting magnets. Superconducting bulk magnets and stacks of tapes have already demonstrated the extraordinary potential to trap magnetic fields of very high order with very compact sizes. This has significantly increased the efficiency of rotating machines and improved power/torque density, while having low synchronous reactance with large overloading capacity, high transient stability with low noise and harmonic content with the additional cost of cooling. This thesis focuses on a new type of superconducting magnet which uses superconducting tape as the field source. The most significant limiting factor for superconducting magnets is their size.;This new superconducting magnet has made possible the development of HTS magnets with flexible sizes by splitting the 2G HTS tapes to form the persistent current rings. By stacking HTS closed loop rings into a compact magnet, our HTS ring magnet has been proven to generate a trapped magnetic field higher than 5 T. The main advantage of the new magnet compared to existing trapped field HTS magnets is that the magnetic field lies parallel to the ab plane of the HTS, leading to higher critical currents in the same magnetic field. This thesis reports our key findings so far. Two different stacking configuration magnet samples were tested using the field cooling magnetization at 25 K and 4.2 K, with magnet diameter 90 mm and 150 mm, respectively. Over 4.6 T of the trapped field has been reported by using Super Power tapes with a field cooling process at 25 K, which is the highest field trapped in the ring magnets for first configuration. A new stacking design was proposed to improve magnetic field distribution within the magnet and has the potential to trap more magnetic field with the estimated trap field of 9.4 T at 4.2 K. A three dimensional model was developed to simulate the performance of the ring magnets, and good agreements between experiment and simulation have been achieved. The new HTS permanent magnet with improved field homogenisation and large diameter is promising for medical imaging applications, as well as propulsion applications

Complex magnetism in noncentrosymmetric magnets

Broken inversion symmetry in a crystal lattice allows an extra term called the Dzyaloshinskii-Moriya (DM) interaction in the magnetic Hamiltonian. The DM interaction tends to align spins in perpendicular orientation and therefore competes with the exchange interaction that favors collinear spins. This competition results in different modulated chiral magnetic structures depending on the relative strength of the two interactions. Skyrmion, soliton and magnetic blue phases are some of the anticipated structures. This dissertation extends the search for these exotic magnetic structures using various techniques to study the magnetism in the noncentrosymmetric magnets Cr11Ge19 [chromium eleven germanium nineteen], Cr1/3NbS2 [chromium one-third niobium disulphide] and K2V3O8 [fresnoite-type potassium vanadate]. Experimental investigations of magnetic, thermal, structural and elastic properties of Cr11Ge19 indicate complex itinerant ferromagnetism, evidence of spin wave excitations, and strong magnetoelastic coupling in this material. First principles calculations support the presence of itinerant ferromagnetism and suggest a noncollinear ground state may be expected. In the chiral helimagnet Cr1/3NbS2 the magnetic transition is found to strongly affect the electrical transport. Spin reorientation from the helimagnetic ground state to the commensurate ferromagnetic state is evident in the magnetoresistance. Neutron scattering is used to demonstrate the change in the periodicity of the incommensurate structure and the eventual incommensurate to commensurate transition, in accordance with the theoretical prediction of the soliton model. The tetragonal easy axis antiferromagnet K2V3O8 has been investigated by DC magnetization, AC susceptibility and heat capacity measurements. Based on the comparison of the behaviors observed in these measurements with other well-studied chiral helimagnets, the existence of two different spiral structures - one parallel and one perpendicular to the c axis - is proposed

Influence of Defects on Critical Parameters in High Temperature Superconductors

Bismuth cuprate high temperature superconductors are currently the only ceramic material that can be successfully processed in kilometer length wires. Bismuth cuprates form three compositions that can be represented with the generic formula Bi2Sr2CanCun+1O8+d n = 0, 1, 2 (with critical temperatures Tc = 20K, 85-94K and 110K respectively). With critical temperatures above 77K (liquid nitrogen boiling point) the only property inhibiting a widespread use is the infield performance, that is, insufficient critical current densities in high magnetic fields. The infield critical current is intimately related to the pinning of the flux vortices that form under the influence of a magnetic field. The intrinsic pinning of flux vortices, is still not well understood in these quaternary systems. The influence of SrCuO2 second phase additions as well as internal cation nonstoichiometry was investigated as a viable way to control the flux pinning properties in the Bi2Sr2CaCu2O8+d (Bi-2212) system. The compositions of Bi2Sr2+xCaCu2+xO8+y (x = 0.0001-0.6) as well as Nd substituted Ca samples were prepared via freeze-drying. Phase pure stoichiometric Bi-2212 was synthesized via freeze-drying in a reduced oxygen atmosphere. It was further determined that up to 20mol% additions of SrCuO2 can be accommodated in the Bi-2212 structure and that the additions increase critical current. The incorporation of SrCuO2 into Bi-2212 results in change of both lattice parameters and modulation vector

Conductor Architecture and Self-Field of Superconducting Strands

Three standard reference material Nb-Ti strands, manufactured for the ITER poloidal field magnets, were extensively characterised using both transport and magnetisation techniques, with a focus on the behaviour of the material in a magnetic field. To quantify the effect of magnetic self-field, the field generated by current flow, the critical current density was measured as a function of the applied magnetic field, temperature, current polarity, and geometry. A high capacity probe was designed and commissioned for the transport measurements. The characterisation in different measurement geometries was possible with custom-built sample holders (i.e., barrels). As the titanium alloy Ti-6Al-4V used in the standard ITER VAMAS barrel is superconducting at 4.22 K, an alternative titanium alloy (Ti-6Al-2Sn-4Zr-2Mo-0.2Si) was identified that is not superconducting at 4.22 K and used to manufacture the barrels. The transport measurements at low applied magnetic-fields resulted in high current densities, and the effect of self-field being large. To investigate the self-field both finite element analysis (FEA) and semi-analytic methods were employed. The H-formulation of Maxwell’s equations was implemented using Comsol Multiphysics, a commercial FEA software. The model input for the superconductors properties were defined using a number of experimental J_C (B) relationships. The architecture of the strand was approximated with different degrees of complexity. The FEA models considered the cross-section of the strand as circular, annular, and as three nested cylinders (i.e., tubes-within-tubes). The probability distribution of the magnetic field components in the superconducting domain was calculated and analysed. The changes in the field distribution due to the geometry of the measurement barrels and the current orientation, (resulting in opposite Lorentz force orientation), were used to quantify the magnitude and orientation of the self-field. A semi-analytic method was used to derive a the magnetic field distribution data from the FEA and the experimental data. The resultant piecewise J_C (B) calculated for the Nb-Ti strand, can be considered a universal J_C (B) relationship

Proceedings of the 4th International Conference and Exhibition: World Congress on Superconductivity, volume 1

The papers presented at the 4th International Conference Exhibition: World Congress on Superconductivity held at the Marriott Orlando World Center, Orlando, Florida, are contained in this document and encompass the research, technology, applications, funding, political, and social aspects of superconductivity. Specifically, the areas covered included: high-temperature materials; thin films; C-60 based superconductors; persistent magnetic fields and shielding; fabrication methodology; space applications; physical applications; performance characterization; device applications; weak link effects and flux motion; accelerator technology; superconductivity energy; storage; future research and development directions; medical applications; granular superconductors; wire fabrication technology; computer applications; technical and commercial challenges, and power and energy applications

Electron-tunneling studies on CeCoIn5 heavy-fermion thin films and microstructures

Investigation of low-temperature electronic properties of MBE grown CeCoIn5 and CeIn3 thin films by means of electron tunneling and quantum electron interference effects