Small-scale Coil Research Articles

Optimal Design and Performance Evaluation of Dual-Capacitor Switching (DCS) Quench Protection System for Superconducting Magnet

In recent years, a new quench protection system using capacitor and switches has been announced to rapidly extract energy from high temperature superconducting (HTS) magnets. When a quench occurs, the quench protection system activates four metal oxide-semiconductor field-effect transistor switches in sequence, and the energy stored in the magnet is extracted by a capacitor to an external resistor. To verify the feasibility of the proposed dual-capacitor switching (DCS) quench protection system, DCS system was tested using a small-scale coil with a 3.3 mH self-inductance. The experimental results show that the energy extraction of the magnet is faster than the quench protection system using a conventional dump resistor. However, as the system is sensitive to the capacitance, inductance, and four resistances, it is necessary to analyze and optimize the design parameters for an application to various magnet systems. In this study, a modified DCS system is introduced to remove the constraints of capacitance, and the effect of all the design parameters on DCS protection performance is analyzed. The optimal design of modified DCS protection system for the best performance is determined. The performance of the system is also evaluated by applying a design that is optimized for the scale-up HTS coil with a 30 mH self-inductance.

Insulation system for high temperature superconductor cables

Large-scale superconductor applications, like fusion magnets, require high-current capacity conductors to limit system inductance and peak operating voltage. Several cabling methods using high temperature superconductor (HTS) tapes are presently under development so that the unique high-field, high-current-density, high operating temperature characteristics of 2nd generation REBCO coated conductors can be utilized in next generation fusion devices. Large-scale magnets are generally epoxy impregnated to support and distribute electromagnetic stresses through the magnet volume. However, the present generation of REBCO coated conductors are prone to delamination when tensile stresses are applied to the broad surface of REBCO tapes; this can occur during epoxy cure, cooldown, or magnet energization. We present the development of an insulation system which effectively insulates HTS cabled conductors at high withstand voltage while simultaneously preventing the intrusion of the epoxy impregnant into the cable, eliminating degradation due to conductor delamination. We also describe a small-scale coil test program to demonstrate the cable insulation scheme and present preliminary test results.

Effects of surface coating and water retention on frost formation in microchannel evaporators (ASHRAE RP-1589)

This study experimentally investigated frost growth on louvered folded fins in outdoor microchannel heat exchangers when used in air-source heat pump systems. The effects of five surface coatings on the thermal and hydraulic performance of the microchannel heat exchangers under frosting conditions were studied. The overall aim was to provide some guidelines about frosting behavior of microchannel heat exchangers with hydrophilic and hydrophobic coatings. The approach taken was to perform laboratory experiments on small-scale coils and several sample fins that were cut out from commercially available heat exchangers. The sample fins were tested in controlled laboratory conditions that replicated those in actual heat pump systems in the winter season. A better estimation of the fin surface temperature was achieved with the methodology developed in the present study. The experimental value of air pressure drop across the coils, time of frost–defrost cycles, and heat transfer rates were recorded for heat exchangers operating in actual transient frosting conditions. Data showed that the frosting time and frost growth rates depended mainly on the local fin surface temperature. Five surface coatings were investigated, and the data show that the hydrophobic coating had slightly lower frosting performance after a few defrost cycles with respect to hydrophilic surface coating.

5T級DI-BSCCO小型コイルの特性評価 (1) -コイルの交流損失-

5T級DI-BSCCO小型コイルの特性評価 (1) -コイルの交流損失-

Formation of sheet plumes, current coils, and helical magnetic fields in a spherical magnetohydrodynamic dynamo

Aiming at understanding of magnetic field generation process in rapidly rotating stars and planets represented by the Earth, computer simulations of magnetohydrodynamic (MHD) dynamo were performed in a rotating spherical shell geometry. Thermal convection and dynamo process with Ekman number of the order of 10−7 were studied. New structures of convection motion, dynamo-generated electrical current, and magnetic field are found. The flow is organized as a set of thin, sheet-like plumes. The current is made of small-scale coil structure with magnetic flux tubes within each of the coil. These flux tubes are connected each other to form a large scale helical magnetic field structure.

Industrialization of Radiation-Resistant Cyanate Ester Magnet Insulation

Future magnet systems require electrical insulation that can withstand high levels of incident radiation, while also providing the necessary mechanical robustness and dielectric strength to operate these devices. Moreover, the insulation must also be compatible with industrial fabrication processes to enable their efficient, large-scale manufacture. Cyanate ester-based insulations provide the necessary electro-mechanical performance and radiation resistance for these applications, but more information is needed to demonstrate application-specific issues related to magnet production. To accomplish this, a series of tests were performed to validate the long-term processing behavior of cyanate ester resins, their adhesion to Kapton, and the fabrication of small-scale coils. The results of this work demonstrated a working time of greater than 85 hours, good adhesion to Kapton, and the successful fabrication of test coils. Larger-scale industrial trials are ongoing at various sites to further demonstrate the use of cyanate ester insulation for the ITER TF coils, as well as commercial applications.

Design of a Radiation Resistant Quadrupole Using CICC

High acceptance fragment separators for secondary beam facilities require large aperture quadrupoles close to the production targets. These quadrupoles are exposed to high levels of radiation. We present designs for superferric quadrupoles based on radiation tolerant Cable-In-Conduit-Conductor (CICC) coils that have lifetime limits set by the superconducting materials. CICC coils using both stainless steel and aluminum conduits are described and small-scale coil fabrication presented

曲げと引張り歪印加時におけるＮｂ３Ｓｎ線材のＩｃ劣化率の導出

Because Nb3Sn superconducting wires have strong strain-sensitivity, it is desired that we can grasp Ic degradation rate analytically when bending and tensile strains are applied to these wires. We fabricated Nb3Sn coils through the react and wind technique in which the wires, processed by our internal-tin method, were primarily reacted, then coated with formal insulation and finally wound to a coil, and we also succeeded in passing the current, which is equivalent to the case of short length wires. An estimate of the Ic degradation rate is needed when bending and tensile strains are applied to the wire for examining the above-mentioned experimental result. Therefore we theoretically analyzed it by considering the shift of neutral axis when the wire was bended, taking the plastic deformation of composite materials into account, and also numerically calculated it. The results were that the neutral axis shifts from the center of the wire toward 72μm inside; the strain range of the Nb3Sn filaments are from 0.40% of maximum value to -0.06% of minimum one when winding the coil; the strain of the filaments increases 0.14% when the coil is cooled to 4.2K; and the additional Hoop's strain of 0.033% is applied to the wire for passing current to the coil. It was estimated that the Ic degradation rate based on the Ic-strain characteristics of the wire becomes 8.5%. This value agrees substantially with the experimental data of our small-scale coil; thus the validity of the calculation on Ic degradation rate can be verified.

Construction and normal zone propagation analysis of high-T/sub c/ superconducting Bi(Pb)-2223/Ag class II coils and magnets

Once the production of high quality long length Bi(Pb)-2223/Ag tapes have been achieved considerations such as fabrication into practical applications without degrading the performance of the tape become the major issues. Here, the application involves the construction of class II coils and magnets. The main problems concerned are usually related to the winding procedures (e.g. wind-react and react-wind), the insulating material, the construction or stacking of coils if they are pancake-shaped and the study of quench propagation parameters. This paper investigates these issues in coil design and construction by means of measurement techniques from small scale coils and magnets made from high-T/sub c/ superconducting Bi(Pb)-2223/Ag composite tapes.

Processing and fabrication of Bi2Sr2CaCu2Ov/Ag tapes and small scale coils

Abstract Optimipation of heat treatment conditions for a Bi2Sr2CaCu2Op(Bi-2212)/Ag melt-solidified tape was carried out. Effects of the maximum temperature for partial melting, cooling rate in solidifying process, cooling rate after the melt-solidification and partial pressure of oxygen on Jc were examined. A tape prepared under optimized conditions showed a high Jc value of 2.4 × 105 A/cm2 at 4.2 K in 12 T. Small pancake coils were fabricated using Bi-2212/Ag long tapes prepared by a continuous dip-coating method. The generated field of a coil was higher than 1 T at 4.2 K in bias fields less than 4 T and its critical current remained greater than 200 A even at 20 K under zero bias field. This means that the Bi-2212/Ag coil has sufficient potential for practical use as a superconductng magnet at 20 K.