Solenoidal Coils Made from Monofilamentary and Multifilamentary MgB2 strands

TL;DR

This study demonstrates the fabrication and testing of MgB2 solenoids made from monofilamentary and multifilamentary strands, showing promising transport properties and homogeneity at cryogenic temperatures.

Contribution

First comprehensive evaluation of MgB2 solenoids with different strand types, including detailed transport measurements and performance comparison.

Findings

Achieved 222 A at 4.2 K in a 7-strand coil

Reached a Jc of 300 kA/cm2 at 4.2 K

Generated magnetic fields up to 1.5 T at 4.2 K

Abstract

Three solenoids have been wound and with MgB2 strand and tested for transport properties. One of the coils was wound with Cu-sheathed monofilamentary strand and the other two with a seven filament strand with Nb-reaction barriers, Cu stabilization, and an outer monel sheath. The wires were first S-glass insulated, then wound onto an OFHC Cu former. The coils were then heat treated at 675C/30 min (monofilamentary strand) and 700C/20 min (multifilamentary strand). Smaller (1 m) segments of representative strand were also wound into barrel-form samples and HT along with the coils. After HT the coils were epoxy impregnated. Transport Jc measurements were performed at various taps along the coil lengths. Measurements were made initially in liquid helium, and then as a function of temperature up to 30 K. Homogeneity of response along the coils was investigated and a comparison to the short sample results was made. Each coil contained more than 100 m of 0.84-1.01 mm OD strand. One of the 7 strand coils reached 222 A at 4.2 K, self field, with a Jc of 300 kA/cm2 in the SC and a winding pack Je of 23 kA/cm2. At 20 K these values were 175 kA/cm2 and 13.4 kA/cm2. Magnet bore fields of 1.5 T and 0.87 T were achieved at 4.2 K and 20 K, respectively. The other multifilamentary coil gave similar results.