Fast and accurate electromagnetic modeling of non-insulated and metal-insulated REBCO magnets

REBCO high-temperature superconductors are promising for fully superconducting high-field magnets, including ultra-high field magnets. Non-insulated (NI) and metal-insulated (MI) windings are a good solution for protection against electro-thermal quench. Design and optimization requires numerical modelling of REBCO inserts for high-field magnets. Here, we detail a fast and accurate two-dimensional (2D) cross-sectional model for the electromagnetic response of NI and MI coils, which is based on the Minimum Electro Magnetic Entropy Production (MEMEP). Benchmarking with an $A-V$ formulation method on a double pancake coil shows good agreement. We also analyse a fully superconducting 32 T magnet with a REBCO insert and a low-temperature superconducing (LTS) outsert. In particular, we analyze the current density, the screening curren induced field (SCIF), and the AC loss. We have shown that metal-insulated coils enable transfer of angular current in the radial direction, and hence magnet protection, while keeping the same screening currents and AC loss of isolated coils, even at relatively high ramp rates of 1 A/s. Surprisingly, soldered coils with low resistance between turns present relatively low AC loss for over-current configuration, which might enable higher generated magnetic fields. The numerical method presented here can be applied to optimize high-field magnets regarding SCIF in MI or NI magnets. It also serves as the basis for future electro-thermal modelling and multi-physics modeling that also includes mechanical properties

A novel and coupled Electromagnetic and Electrothermal software for quench analysis of high field magnets

High-field REBCO magnets contain several coils with many turns. {For these magnets,} electro-thermal quench is an issue that magnet designers need to take into account. Thus, there is a need for fast and accurate software to numerically model the overall performance of full-scale magnets. High temperature superconductors can be modeled using different techniques for electro-magnetic (such as $H$-formulation and $A-V$ formulation) and thermal (finite element method) analysis. However, it takes a lot of time to model the electro-magnetic and electro-thermal behavior of superconductors simultaneously in a commercial software, especially for non-insulated or metal-insulated coils. We have developed a novel software programmed in C++, which performs coupled electro-magnetic and electro-thermal analysis using variational methods based on Minimum Electro-Magnetic Entropy Production (MEMEP) and Finite Difference, respectively. The developed software is applied to axi-symmetric fullscale magnets of more than 30 T field strength for transient design (thermal quench reliability), taking screening currents into account. We show that the magnets incorporating non-insulated coils {are more reiable against quench} than the metal insulated coils. Also, {realistic} cooling conditions at boundaries is essential for such simulations. The model developed can be used for a quick and complete electro-magnetic and electro-thermal analysis of superconducting high field magnets.Comment: Improved figures. Corrected tex

The Gut Microbiota Regulates Intestinal CD4 T Cells Expressing RORγt and Controls Metabolic Disease

SummaryA high-fat diet (HFD) induces metabolic disease and low-grade metabolic inflammation in response to changes in the intestinal microbiota through as-yet-unknown mechanisms. Here, we show that a HFD-derived ileum microbiota is responsible for a decrease in Th17 cells of the lamina propria in axenic colonized mice. The HFD also changed the expression profiles of intestinal antigen-presenting cells and their ability to generate Th17 cells in vitro. Consistent with these data, the metabolic phenotype was mimicked in RORγt-deficient mice, which lack IL17 and IL22 function, and in the adoptive transfer experiment of T cells from RORγt-deficient mice into Rag1-deficient mice. We conclude that the microbiota of the ileum regulates Th17 cell homeostasis in the small intestine and determines the outcome of metabolic disease

Experimental Measurement and Numerical Simulation of the Screening Current-Induced Field Decay in a Small ReBCO Coil

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Investigation on Two Techniques for the Reduction of Screening Current-Induced Field Effects in REBCO HTS Coils

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Experimental measurements of contact resistivity between superconducting HTS tapes with or without metallic co-wound tape

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Analytical formulation of mechanical stresses in no-impregnated, multi-layer solenoids

International audienceThis paper develops and summarizes analytical formulations of radial and tangential stresses of superconducting, no-impregnated solenoids, based on a multilayer model. The analysis takes into account the fabrication steps (pre-winding and reinforcement), cooling-down and energization of the coil (magnetic loading). Both isotropic and orthotropic cases are considered. Representative calculations for metal-as-insulation coils are presented and benchmarked against FEM computations with the CAST3M code

Full-Field Displacement Measurement within a Metal-as-Insulation HTS Pancake

International audienceIn situ measurement of metal-as-insulation (MI) high temperature superconductor (HTS) pancake magnet deformation gives insight to its actual mechanical state. Measurement of hoop strain for inner / outer turn of MI pancake is possible locally using strain gauges. Hence, to avoid this local measurement limit, non-contact full-field displacement measurement is adopted. This technique is based on digital image correlation (DIC), which derives the displacement field in specified region of interest (ROI) by correlation between the deformed state image and the reference state image