We have built and tested a thin-film high temperature superconducting (HTS) surface coil for MRI at 0.064T. When placed as close as possible to a conductive sample, the 6.7-cm outer diameter HTS coil had a measured signal-to-noise ratio (SNR) 1.8 times higher than a room temperature copper coil of similar size and location. Our results predict that in some cases, SNR gains of about a factor of 2 can be attained in low-field MRI systems by substituting HTS surface coils for copper coils.

A chemical deposition process for the preparation of superconducting thin films of Tl2CaBa2Cu2O8 (2122) and Tl2Ca2Ba2Cu3O10 (2223) has been developed. Oriented, superconducting 2122 and 2223 thin films have been successfully fabricated on single-crystal yttria-stabilized zirconia and magnesium oxide substrates (〈100〉 orientation). Epitaxial films have been prepared on magnesium oxide. Chemical analysis of the film composition by energy dispersive x-ray analysis is in agreement (2122 vs 2223) with the phases indicated by powder x-ray diffraction. The thin films of these compounds exhibited superconducting transition temperatures above 105 K as determined by variable-temperature resistivity and ac magnetic susceptibility measurements. In addition, microwave surface resistance measurements at 150 GHz show that these films have very low losses at 77 K (1 mΩ).

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Detailed measurements have been made of the magnetic field (0<H<6 T) and temperature (10 K<T<100 K) dependencies of the critical current density jc in Tl2CaBa2Cu2O8 films before and after irradiation with incremental fluences (0<Φ<3×1016 cm−2) of 2 MeV protons. The results are interpreted quantitatively in terms of radiation-induced changes in (1) the critical temperature, (2) the rate of thermal flux creep, and (3) local scale superconductivity. Radiation-induced enhancements in jc are described by an expression which allows the fluence that maximizes jc to be predicted as a function of H, T, pinning energy, and particle type.

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