Mechanism of the High-Tc Superconducting Dynamo: Models and Experiment

High-Tc superconducting (HTS) dynamos are experimentally proven devices that can produce large, >kA, DC currents in superconducting circuits, without the thermal leak associated with copper current leads. However, these DC currents are theoretically controversial, as it is not immediately apparent why a device that is topologically identical to an AC alternator should give a DC output at all. Here, we present a finite-element model, and its comparison with experiment, which fully explains this effect. It is shown that the DC output arises naturally from Maxwell’s laws, when time-varying overcritical eddy currents are induced to circulate in an HTS sheet. We first show that our finite-element model replicates all of the the experimental electrical behavior reported so far for these devices, including the DC output characteristics, and transient electrical waveforms. Direct experimental evidence for the presence of circulating eddy currents is also obtained through measurements of the transient magnetic field profile across the HTS tape, using a linear Hall array. These results are also found to closely agree with predictions from the finite-element model. Following this experimental validation, calculated sheet current densities and the associated local electric fields are examined for a range of frequencies and net transport currents. We find that the electrical output from an HTS dynamo is governed by the competition between transport and eddy currents induced as the magnet transits across the HTS tape. These eddy currents are significantly higher (∼1.5X) than the local critical current density J_c, and hence experience a highly non-linear local resistivity. This non-linearity breaks the symmetry observed in a normal ohmic material, which usually requires the net transport current to vary linearly with the average electric field. The interplay between local current densities and non-linear resistivities (which both vary in time and space) is shown to systematically give rise to the key observed parameters for experimental HTS dynamo devices: the open-circuit voltage V_oc, the internal resistance R_int, and the short-circuit current I_sc. Finally, we identify that the spatial boundaries formed by each edge of the HTS stator tape play a vital role in determining the total DC output. This offers the potential to develop new designs for HTS dynamo devices, for which the internal resistance is greatly reduced and the short circuit current is substantially increased.New Zealand (NZ) MBIE Endeavour Grant No. RTVU1707 NZ Royal Society Marsden Grant No. MFP-VUW1806

A Trapped Field of 17.6 T in Melt-Processed, Bulk Gd-Ba-Cu-O Reinforced with Shrink-Fit Steel

The ability of large grain, REBa$_{2}$Cu$_{3}$O$_{7-\delta}$ [(RE)BCO; RE = rare earth] bulk superconductors to trap magnetic field is determined by their critical current. With high trapped fields, however, bulk samples are subject to a relatively large Lorentz force, and their performance is limited primarily by their tensile strength. Consequently, sample reinforcement is the key to performance improvement in these technologically important materials. In this work, we report a trapped field of 17.6 T, the largest reported to date, in a stack of two, silver-doped GdBCO superconducting bulk samples, each of diameter 25 mm, fabricated by top-seeded melt growth (TSMG) and reinforced with shrink-fit stainless steel. This sample preparation technique has the advantage of being relatively straightforward and inexpensive to implement and offers the prospect of easy access to portable, high magnetic fields without any requirement for a sustaining current source.Comment: Updated submission to reflect licence change to CC-BY. This is the "author accepted manuscript" and is identical in content to the published versio

Saquinavir Loaded Acetalated Dextran Microconfetti – a Long Acting Protease Inhibitor Injectable

Since the adoption of highly active antiretroviral therapy, HIV disease progression has slowed across the world; however, patients are often required to take multiple medications daily of poorly bioavailable drugs via the oral route, leading to gastrointestinal irritation. Recently, long acting antiretroviral injectables that deliver drug for months at a time have moved into late phase clinical trials. Unfortunately, these solid phase crystal formulations have inherent drawbacks in potential dose dumping and a greater likelihood for burst release of drug compared to polymeric formulations

Numerical optimisation of mechanical ring reinforcement for bulk high-temperature superconductors

The finite element method has been used extensively in recent years to solve various problems related to applied superconductivity and provides a useful tool for analysing and predicting experimental results. Based on a recently-developed modelling framework, implemented in the finite element software package COMSOL Multiphysics, investigations on the minimum ring reinforcement required to prevent mechanical failure in bulk high-temperature superconducting magnets have been carried out. Assuming homogeneous J$_{c}$(B,T) across the bulk sample irrespective of its dimensions, the maximum magnetic stresses experienced, and the minimum ring thickness required to prevent the hoop and radial stresses from exceeding the tensile strength of the bulk superconductor have been determined for varying values of the Young\u27s modulus, radius, height and temperature of a representative single-grain Ag-containing Gd-Ba-Cu-O bulk sample. This comprehensive analysis details the influence each of these key parameters has on the magnetic stress and hence their impact on the necessary ring thickness to prevent mechanical failure in any given system, i.e., for any combination of material properties and sample dimensions

Numerical optimisation of mechanical ring reinforcement for bulk high-temperature superconductors

Abstract: The finite element method has been used extensively in recent years to solve various problems related to applied superconductivity and provides a useful tool for analysing and predicting experimental results. Based on a recently-developed modelling framework, implemented in the finite element software package COMSOL Multiphysics, investigations on the minimum ring reinforcement required to prevent mechanical failure in bulk high-temperature superconducting magnets have been carried out. Assuming homogeneous Jc (B,T) across the bulk sample irrespective of its dimensions, the maximum magnetic stresses experienced, and the minimum ring thickness required to prevent the hoop and radial stresses from exceeding the tensile strength of the bulk superconductor have been determined for varying values of the Young’s modulus, radius, height and temperature of a representative single-grain Ag-containing Gd-Ba-Cu-O bulk sample. This comprehensive analysis details the influence each of these key parameters has on the magnetic stress and hence their impact on the necessary ring thickness to prevent mechanical failure in any given system, i.e., for any combination of material properties and sample dimensions

Reliable 4.8 T trapped magnetic fields in Gd-Ba-Cu-O bulk superconductors using pulsed field magnetization

Abstract A robust and reliable in-situ magnetization method is essential for exploiting the outstanding magnetic flux trapping ability of bulk superconductors in practical applications. We report a 4.8 T peak trapped magnetic field, B T, achieved at 30 K in a 36 mm diameter GdBa2Cu3O7-δ –Ag bulk superconductor using pulsed field magnetization (PFM). To realize this, we have developed a reliable two-step multi-pulse PFM process based on understanding and exploiting the avalanche-like flux jump phenomenon observed in these materials. The magnitude of the applied pulsed magnetic field (B a) necessary to trap 4.8 T was merely 5.29 T, corresponding to a remarkable magnetization efficiency (B T/B a) of 90%.This study was supported by the Engineering and Physical Sciences Research Council (No. EP/P00962X/1), the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB25000000), the National Key R&D Program (2016YFF0101701) and the project (6140923050202). M D Ainslie would like to acknowledge financial support from an Engineering and Physical Sciences Research Council (EPSRC) Early Career Fellowship, EP/P020313/

Off the Couch and Onto the Streets: Toward an Ethnographic Psychoanalysis

Psychoanalysis has much to gain by incorporating ethnographic methods into its repertoire. Recent works in ethnographic psychoanalysis demonstrate how psychoanalysis stands to function better as both community intervention and participatory action research. This article describes the historical convergence between psychoanalysis and cultural anthropology and situates ethnographic psychoanalysis within interdisciplinary theory and practice