Process to densify Bi2Sr2CaCu2OX round wire with overpressure before coil winding and final overpressure heat treatment. (7th January 2020)

• Record Type: Journal Article
• Authors: Matras, M R; Jiang, J; Trociewitz, U P; Larbalestier, D C; Hellstrom, E E
• Is Part Of: Superconductor science & technology. Volume 33:Number 2(2020:Feb.)
• Publication Date: 2020-01-07
• Subjects: Bi2Sr2CaCu2OX (2212) round wires -- partial-melt process -- high temperature superconductor -- overpressure -- wire densification -- solenoid magnets; Superconductivity -- Periodicals; Superconductors -- Periodicals; 537.623
• DOI: 10.1088/1361-6668/ab5ad6
• Languages: English
• ISSNs: 0953-2048

Abstract

Abstract: Overpressure (OP) processing of wind-and-react Bi2 Sr2 CaCu2 O x (2212) round wire compresses the wire to almost full density, decreasing its diameter by about 4% without change in wire length and substantially raising its J C . However, such shrinkage can degrade coil winding pack density and magnetic field homogeneity. To address this issue, we here present an overpressure predensification (OP-PD) heat treatment process performed before melting the 2212, which greatly reduces wire diameter shrinkage during the full OP heat treatment (OP-HT). We found that about 80% of the total wire diameter shrinkage occurs during the 50 atm OP-PD before melting. We successfully wound such pre-densified 1.2 mm diameter wires onto coil mandrels as small as 10 mm diameter for Ag–Mg-sheathed wire and 5 mm for Ag-sheathed wire, even though such small diameters impose plastic strains up to 12% on the conductor. A further ∼20% shrinkage occurred during a standard OP-HT. No 2212 leakage was observed for coil diameters as small as 20 mm for Ag–Mg-sheathed wire and 10 mm for Ag-sheathed wire, and no J C degradation was observed on straight samples and 30 mm diameter coils.