‘Defect-irrelevant-winding’ no-insulation (RE)Ba 2 Cu 3 O 7 − x pancake coil in conduction-cooling operation

This study is a sequel to our previous study on a 38 mm diameter cold bore metal-as-insulation (MI) HTS insert that reached 32.5 T in a 18 T background magnetic field. For refurbishing, 7 MI double-pancake (DP) coils were re-wound with used REBCO tapes to just replace the damaged HTS pieces by new ones at inner junctions. 2 DP coils were fully fabricated using new REBCO tapes. The new assembled insert was then tested under various background magnetic fields at 4.2 K. The key focuses of this paper are: 1) the damages in the DP coils; 2) their repair; 3) the characteristics resistance change of the insert; 4) the resistance value of each DP coil; 5) the maximum field of the HTS-resistive hybrid magnet; and 6) the field stability estimation of the hybrid by NMR characterization.

Section: A Investigation Of Conductor and Joints After Two Quench Eventsmentioning

confidence: 99%

Metal-as-Insulation HTS Insert for Very-High-Field Magnet: A Test Report After Repair

Song

Chaud

Debray

et al. 2022

“…Further studies in development of REBCO magnet technology should account for this behavior. In addition, heat generation due to current sharing in a no-insulation coil or cable should be considered, in particular for conduction-cooled magnet applications [22]. The model may be used to study the impact of electrical contact resistances between conductor turns to regulate current sharing [18].…”

Section: Discussionmentioning

confidence: 99%

Analysis of Defect Irrelevancy in a Non-Insulated REBCO Pancake Coil Using an Electric Network Model

Webb-Mack

Wang

2022

High-temperature superconducting REBCO coated conductor is one of the main candidates for next-generation high field magnets in fusion reactors and particle accelerators owing to their high current-carrying capability. Although these materials can operate at higher temperatures and generate higher magnetic fields than their counterparts with lower critical temperatures, protecting the REBCO magnet against quench is challenging. A variety of candidate technologies that may be able to enable self-protection, including no-insulation technology and insulative coatings with temperature-dependent resistance, are in development. In order to understand current sharing and thermal processes during a quench, we model a REBCO pancake coil as an electrical circuit, considering power generation and heat transfer along conductor turns, and study the current distribution around a local defect with lower critical current. The magnetic field and coil terminal voltage predicted by the simulation was compared to published experimental results. Our results provide useful insights into how current sharing occurs around defects.

“…NTRINSICALLY, local defects reduce local critical currents and are not avoidable in a coated conductor even by using the most advanced manufacturing technology [1][2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Thermal Runaway of Conduction-Cooled Monofilament and Multifilament Coated Conductors

Luo

Zhao

Sogabe

et al. 2022

We experimentally studied the thermal runaway initiating at a low critical current (Ic) part. This low Ic part is determined by the combination of two reasons in a real coil: (a) the unavoidable defects caused by the manufacturing process, which reduce local critical currents (and might not be uniform across the width of a coated conductor) and (b) the magnetic field distribution along the coated conductor. To simulate the thermal runaway using a short monofilament/multifilament REBa2Cu3Oy (RE-123) coated conductor, we artificially created a local defect (low Ic part) in a short sample by pressing using a drill bit (creating a defect close to one edge of a coated conductor) or bending (creating a uniform defect across the width of a coated conductor). The sample of the coated conductor was conduction-cooled to 30 K, and a magnetic field was applied (µ0H up to 2 T) perpendicular to the wide face of the conductor to control its critical current. Transverse voltages in a multifilament coated conductor were measured to obtain the transverse currents among the filaments through the copper layer. Thermal runaway currents (operating currents above which thermal runaway initiates) of the monofilament sample and those of the multifilament sample with additional Joule loss due to the transverse currents were determined and compared to study the effect of the transverse currents on the initiation of thermal runaway in the multifilament coated conductor. Experiments on the protection against thermal runaway were conducted. When a normal voltage (over a preset threshold) was detected, the supplied current would be decreased exponentially. The thresholds for protecting monofilament and multifilament coated conductors from degradation after thermal runaway were compared.