Electrical Characteristics of Soldered Metal Insulation REBCO Coil

In this article, we summarize what we have learned about Metal-as-Insulation (MI) winding behavior and technical challenges. Bailey et al. first proposed the use of Metallic Insulation (MI) for superconducting magnet in 1988 through a U.S. patent. High Temperature Superconductor (HTS) materials are highly thermally stable. This feature compared to classical Low Temperature Superconductor (LTS) enables the use of MI technology to improve the protection against quenches. Gupta was the first to propose the use of a metallic tape in an HTS winding to avoid too much radial currents in No Insulation (NI) in 2011. Hahn et al. presented preliminary results on a pancake sample the same year. We are proposing here to come back on the work done for about 10 years by research groups worldwide and will focus on the turn-to-turn contact resistivity Rct parameter. We will also give details of our LNCMI-CEA-Néel Institute MI HTS insert built in 2018 in the framework of the French National Research Agency (ANR) funding through the NOUGAT project. We tested this magnet many times between 2018 and 2021 and learnt a lot on this technology. This magnet is the first REBCO solenoid of this size using this technology and tested intensively at such high magnetic field (up to 32.5 T) so far. In this magnet, we firstly include a magnetic shielding technology consisting of REBCO NI turns inside the overbanding of each pancake. We give some details and effect of such technology inside an HTS MI insert in case of a fast discharge, a quench or an outsert failure. Finally, we discuss about the self-protection feature of MI coils and we propose a passive protection way for high Rct values.

Section: The Contact Resistivity: a Key Parameter For Transient Behaviorsupporting

confidence: 64%

Metal-as-insulation HTS coils

Lécrevisse¹,

Chaud

Fazilleau³

et al. 2022

“…To advance the development of metal-insulation coils, it is necessary to systematically examine their thermoelectromagnetic properties. At present, considerable studies have been carried out [21][22][23][24][25], but most of them were qualitative and experimental [21][22][23], being insufficient to characterize the redistribution of the current and the thermal distribution in the coil. In addition, the continuous changing of the contact resistance to obtain an optimal value is mostly inaccessible from the experiments.…”

Section: Introductionmentioning

confidence: 99%

Thermo-electromagnetic modeling of coated superconductor coils with metal insulation

Wang

Zhou

et al. 2021

The use of metallic sheets as the insulator in a coated superconductor coil is able to increase its turn-to-turn contact resistance for shortening the charging/discharging delay while preserving the self-protection ability. To theoretically understand and predict the properties of the metal-insulation coils, we developed a thermo-electromagnetic model, in which a modified equivalent circuit for electrically representing the metal-insulation coils is built to take the effect of insulator into account. The effectiveness and versatility of this model are verified by different experimental scenarios, e.g., charging, sudden-discharging, and overcurrent. Enabled by the validated model, we carried out a set of case studies and observed that, (a) the metal-insulation coil with a low resistivity and high thermal conductivity metallic insulator is preferable to achieve a better thermal stability; (b) there exists an optimal insulator thickness for realizing the shortest charging delay, but a thicker insulator is superior for realizing a stronger thermal stability; (c) contact resistivity of over 104 μΩ· cm2 can weaken the current sharing in the radial direction, which would deteriorate the thermal stability of the metal-insulation coils, although it can significantly suppress the charging delay, implying that a tradeoff is always needed to balance the charging delay and thermal stability when determining the contact resistivity. These findings, mostly being inaccessible from the experiments, provide guidance toward practical applications of metal-insulated coated superconductor coils.

“…The average resistance of individually measured six inner joints was 176.3 nΩ with a standard deviation of 1.8 nΩ and the average characteristic resistance, R c , representing an average radial-direction resistance of the NI DP coil, was 4.3 mΩ with a standard deviation of 0.3 mΩ.After finishing the initial liquid nitrogen test, we have applied In 52 Sn 48 solder on the top and bottom surfaces of each DP coil as an extra shunting for the extreme NI coil. This extra shunting reduces the contact resistance between turns and provides additional current paths if any defective part appears inside the coil[17,18].…”

mentioning

confidence: 99%

Construction and test result of an all-REBCO conduction-cooled 23.5 T magnet prototype towards a benchtop 1 GHz NMR spectroscopy

Lee¹,

Park²,

Bascuñán³

et al. 2022

A compact benchtop high-ﬁeld REBCO NMR is one of the most promising HTS applications. An all-REBCO, conduction-cooled magnet is a very attractive design option for demonstrating the unique potential of REBCO for forefront magnets. In this research, we have successfully constructed and tested a prototype all-REBCO, conduction-cooled, 23.5 T magnet operating at 10 K. We have applied the concept of an extreme No-Insulation (NI) winding technique, coupled with a solder-shunting procedure to improve magnet performance. We have also used a temperature-controlled charging sequence (TCCS) to reduce the screening current. The magnet was energized to 23.6 T at 14 K; it was further operated to 25 T at 10 K for nearly 60 hours.