Strain Dependence of Critical Current in Bi2212 W & R Wires Under Magnetic Field Up to 30 T

We developed a Walters spring (WASP) type apparatus to investigate the strain dependence of critical current for relatively long superconducting wires under magnetic field. A 72 cm long Bi2212 wind-and-react (W & R) wire was soldered over the whole length on the Cu-Be spring jig and tensile strain was applied by twisting the spring. The probe was inserted in the variable temperature cryostat with He gas flow. Temperature at the current electrodes was controlled by flowing He gas and the heater, in order to reduce heating up during V-I measurement. The probe and cryostat were inserted in the bore of a hybrid magnet in Tsukuba Magnet Laboratory which can generate magnetic field up to 30 T. The result at 6 K under 30 T showed that critical current does not change largely up to a tensile strain of 0.50% at which 95% of critical current compared to its original value is maintained. Thermal expansion measurement was carried out between 290 K and 5 K to consider influence of additional pre-strain from the Cu-Be spring. It was confirmed that the difference in thermal expansion between the Bi2212 composite wire and Cu-Be plate is within 0.01% and this ensures that the Cu-Be spring has little influence on the obtained strain dependence of critical current for the Bi2212 wire