High-magnetic-field transport properties of Bi2Sr2CaCu2O8 single crystals

Gradient coil design using Bi-2223 high temperature superconducting tape for magnetic resonance imaging

Bi-2223 tape is a low-cost, long-length high temperature superconducting material. The new application of Bi-2223 tape for gradient coils for magnetic resonance imaging (MRI) is studied in this paper. Because Bi-2223 tape has a much higher critical current density and a much lower power loss than copper, a Bi-2223 high temperature superconductor (HTS) gradient coil shows great advantages in high gradient strengths, long continuous gradient rating, and free of cooling system over a copper gradient coil. The power losses of Bi-2223 tapes at working frequencies of gradient coils are compared to copper. The critical current degradation of tapes is also discussed. A prototype of HTS tape gradient coil is fabricated and its gradient field distributions are measured. Technical issues of resistance, gradient strength, continuous gradient rating, and cryostat are also discussed.

Investigation of Bi-2223 high temperature superconducting tape as the material for gradient coil in MRI

The use of Bi-2223 high temperature superconducting (HTS) tape as a material for gradient coils in MRI is evaluated in this paper. Bi-2223 tapes have a very high critical current and a very low power loss. A HTS tape gradient coil is expected to provide much higher gradient strength and generate much lower heating than a copper coil. Measurements of the AC power loss of Bi-2223 tapes at typical operating frequencies for gradient coils are presented. The degradation of the critical current and its effect on the increase of AC power loss is analyzed. Practical technical issues such as resistance, gradient strength and mechanical performance are also discussed. A prototype Bi-2223 HTS tape gradient coil is evaluated to verify the concept.

High-field quasiparticle tunneling in Bi2Sr2CaCu2O(8+delta): negative magnetoresistance in the superconducting state

We report on the c-axis resistivity rho(c)(H) in Bi(2)Sr(2)CaCu(2)O(8+delta) that peaks in quasistatic magnetic fields up to 60 T. By suppressing the Josephson part of the two-channel (Cooper pair/quasiparticle) conductivity sigma(c)(H), we find that the negative slope of rho(c)(H) above the peak is due to quasiparticle tunneling conductivity sigma(q)(H) across the CuO2 layers below H(c2). At high fields (a) sigma(q)(H) grows linearly with H, and (b) rho(c)(T) tends to saturate ( sigma(c) not equal0) as T-->0, consistent with the scattering at the nodes of the d-wave gap. A superlinear sigma(q)(H) marks the normal state above T(c).