This paper reports a study of HTS pancake coils without turn-to-turn insulation. Three no-insulation (NI) pancake coils were wound: each single and double pancake coil of Bi2223 conductor and one single pancake of ReBCO conductor. An equivalent electrical circuit for modeling NI coils was verified by two sets of test: 1) charge-discharge; and 2) sudden discharge. Also, an overcurrent test in which a current exceeding a coil's critical current by 2.3 times was performed, and analysed, to demonstrate that in terms of stability NI HTS coils outperform their counterparts. The new NI winding offers HTS coils enhanced performance in three key parameters: overall current density; thermal stability; and mechanical integrity.

HTS Pancake Coils Without Turn-to-Turn Insulation

Issues associated with the exposure of patients to strong, static magnetic fields during magnetic resonance imaging (MRI) are reviewed and discussed. The history of human exposure to magnetic fields is reviewed, and the contradictory nature of the literature regarding effects on human health is described. In the absence of ferromagnetic foreign bodies, there is no replicated scientific study showing a health hazard associated with magnetic field exposure and no evidence for hazards associated with cumulative exposure to these fields. The very high degree of patient safety in strong magnetic fields is attributed to the small value of the magnetic susceptibility of human tissues and to the lack of ferromagnetic components in these tissues. The wide range of susceptibility values between magnetic materials and human tissues is shown to lead to qualitatively differing behaviors of these materials when they are exposed to magnetic fields. Mathematical expressions are provided for the calculation of forces and torques.

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Safety of Strong, Static Magnetic Fields

PURPOSE: To develop a superconducting magnetic resonance (MR) imager that provides direct access to the patient and permits interactive MR-guided interventional procedures. MATERIALS AND METHODS: A 0.5-T superconducting magnet that allows a region of vertical access to the patient was designed and constructed. This magnet was integrated with newly designed shielded gradient coils, flexible surface coils, and nonmagnetic displays and with position-monitoring probes and device-tracking instrumentation. RESULTS: The magnet homogeneity was 12.3 ppm, and the gradient field was linear to within 1% over an imaging region 30 cm in diameter. The signal-to-noise ratio was 10% higher than in a comparable 0.5-T superconducting imager. Images were obtained in several anatomic regions with use of routine pulse sequences. Interactive image plane selection and near real-time imaging, with use of fast gradient-recalled echo sequences, were demonstrated at a rate of one image every 1.5 seconds. CONCLUSION: MR-guided interv...

Superconducting open-configuration MR imaging system for image-guided therapy.

Numerical modeling of superconductors is widely recognized as a powerful tool for interpreting experimental results, understanding physical mechanisms, and predicting the performance of high-temperature-superconductor (HTS) tapes, wires, and devices. This is particularly true for ac loss calculation since a sufficiently low ac loss value is imperative to make these materials attractive for commercialization. In recent years, a large variety of numerical models, which are based on different techniques and implementations, has been proposed by researchers around the world, with the purpose of being able to estimate ac losses in HTSs quickly and accurately. This paper presents a literature review of the methods for computing ac losses in HTS tapes, wires, and devices. Technical superconductors have a relatively complex geometry (filaments, which might be twisted or transposed, or layers) and consist of different materials. As a result, different loss contributions exist. In this paper, we describe the ways of computing such loss contributions, which include hysteresis losses, eddy-current losses, coupling losses, and losses in ferromagnetic materials. We also provide an estimation of the losses occurring in a variety of power applications.

Computation of Losses in HTS Under the Action of Varying Magnetic Fields and Currents

The wind turbine market is growing rapidly, and there has also been a trend toward ever increasing turbine rating. Most turbines to date has used geared high speed generators, but a history of gearbox reliability problems have turned many turbine manufacturers towards direct drive generators, which are very low speed, high torque, and therefore very large. Superconducting machines offer the possibility of much more compact machines, but the high cost of HTS wire to date has prevented their application to a cost sensitive market such as wind energy. A new generation of low cost HTS wire is being developed which will allow HTS machines to compete in such a market. Consequently, converteam are undertaking a project to design a full size direct drive HTS generator, including the manufacture and test of a scaled model generator. The 1st stage conceptual design phase, including economic assessment, has completed which has identified solutions to the anticipated challenges and risk.

A Direct Drive Wind Turbine HTS Generator

Superconducting magnets have become essential components of hadron accelerator/colliders and compact electron accelerators. Their technology has greatly progressed in recent years thanks to the Tevatron and HERA operation experience, the production of the RHIC magnets and the intense R&D programs for SSC, UNK and LHC. For the LHC, at present the most important and advanced project, dipoles, quadrupoles and corrector R&D magnets have been successfully built in industry and laboratories. Major milestones have been recently passed with test and measurement of several industry made, 10 m long, twin-aperture dipoles and the successful operation of a "string" test facility simulating the basic machine half-cell.

http://ieeexplore.ieee.org/iel3/3749/10949/00505200.pdf

R. Perin

Papers

Superconducting magnets