A Feasibility Study of High-Strength Bi-2223 Conductor for High-Field Solenoids

Fabrication and Testing of a Bi-2223 Test Coil for High Field NMR Magnets

In 2005 the Committee on Opportunities in High Magnetic Fields (COHMAG) issued a challenge to develop a 30 T high-resolution NMR magnet. In response, the National High Magnetic Field Laboratory (NHMFL) is investigating all three commercially available high-temperature superconductors (HTS) including REBCO, Bi-2212 and most recently, a reinforced Bi-2223 conductor supplied by Sumitomo Electric, designated Type HT-NX. Recent investigations of Type HT-NX conductor at the NHMFL and by others suggest that operation at hoop stress above 400 MPa, and total strain above 0.7% may be feasible. We have fabricated a test coil from a single 240 m length of HT-NX. The coil was successfully operated to 19.5 T in a 14 T background field, with a total applied strain of 0.8% and coil current density of 243 A/mm2. The coil was cycled 20 times from half the design current to full current without observed degradation.

Bi-2223 Test Coils for High Resolution NMR Magnets

Recently, significant improvement in the strain tolerance of Bi-2223 conductor has been achieved by lamination with high strength nickel alloy. The conductor, supplied by Sumitomo Electric and designated Type HT-NX, is now commercially available in lengths sufficient for manufacture of high-homogeneity solenoids. A program to fully exploit the improved conductor properties is now underway at the National High Magnetic Field Laboratory (NHMFL). Five coils are being made, the last of which is to demonstrate an NMR measurement approaching 1 GHz and 1 ppm over 10 mm volume. In so doing, we expect to demonstrate critical current fraction, and strain similar to that expected in 30 T NMR magnets. The coils will be tested inside an existing 16 Tesla large-bore background magnet at the NHMFL. The design of the NMR demonstration coil is presented first, with expected values for field, homogeneity and strain given. A technology development program is then outlined, which includes fabrication of four test coils to test various design features, develop fabrication tooling and train personnel.