For the first time in nuclear magnetic resonance (NMR) magnet development, a magnet configuration comprising an insert wound with high-temperature superconductor (HTS) and a background-field magnet wound with low-temperature superconductor (LTS) has been proven viable for NMR magnets. This new LTS/HTS magnet configuration opens the way for development of 1 GHz and above NMR magnets. Specifically, a 700 MHz LTS/HTS NMR magnet (LH700), consisting of a 600 MHz LTS magnet (L600) and a 100 MHz HTS insert (H100), has been designed, built, and successfully tested, and its magnetic field characteristics were measured and analyzed. A field homogeneity of 172 ppm in a cylindrical mapping volume of 17 mm diameter by 30 mm long was measured at 692 MHz and corresponding 1 H NMR signal with 1.9 kHz half-width was captured. Two techniques, room-temperature and ferromagnetic shimming, were analytically examined to investigate if they would be effective for further improving spatial field homogeneity of the LH700. This paper reports on a world-first low-/high-temperature superconductor (LTS/HTS) 700 MHz nuclear magnetic resonance (NMR) magnet (LH700), designed, built, and successfully tested at the MIT Francis Bitter Magnet Laboratory (FBML). In the LH700, a 100 MHz HTS insert (H100) was placed in the cold bore of a 600 MHz LTS magnet (L600). Although a 950 MHz all-LTS NMR magnet is the latest achievement, 1 it is generally agreed among magnet engineers that 1 GHz is the practical frequency limit for all-LTS NMR magnets. We believe that the HTS capable of functioning at magnetic fields substantially greater than those of the LTS will play an increasingly prominent role in NMR magnets with operating frequency of 1 GHz and above.The key design philosophy adopted for the H100 includes (1) use of Bi2223-Ag composite tape and (2) a magnet configuration of stacked double-pancake (DP) coils-both for the first time in the history of NMR magnet development. Advantages of the DP coil-based HTS insert include (1) a conductor length typically required, <~200 m, for one DP coil is much less than that necessary, >5000 m, for its layer-wound counterpart, because it is much easier to obtain HTS tape meeting design specifications in short rather than long lengths; (2) DP-coil assembly permits placement of each DP coil, at an axial position within the insert assembly, according to the B ext versus I c characteristics of an individual DP coil that are most favorable to its currentcarrying capacity, thereby maximizing the overall critical current density; (3) axial space between adjacent DP coils may be varied for field profiling with spacers of different thicknesses between DP coils; and (4) in a DP-coil assembly, only defective DP coils need to be replaced rather than the entire insert, as it would be with a layer-wound insert.The H100 consisted of 48 DP coils, each wound with stainless steel reinforced Bi2223-Ag three-ply tape manufactured by American Superconductor Corp. (AMSC). Every DP coil in the H100 was wound in house, with a windi...
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