Design of a conduction-cooled 9.4 T REBCO magnet for whole-body MRI systems

Abstract

A project on the development of REBa2Cu3O7−δ (REBCO) magnets for ultra-high-field magnetic resonance imaging (MRI) was started in 2013. Since REBCO-coated conductors feature high mechanical strength under tensile stress and high critical current density, use of REBCO coils would allow superconducting magnets to be made smaller and lighter than conventional ones. In addition, a conduction-cooled superconducting magnet is simpler to use than one cooled by a liquid helium bath because the operation and maintenance of the cryogenic system become simpler, without the need to handle cryogenic fluid. Superconducting magnets for MRI require homogeneous, stable magnetic fields. The homogeneity of the magnetic field is highly dependent on the coil shape and position. Moreover, in REBCO magnets, the screening-current-induced magnetic field, which changes the magnetic field distribution of the magnet, is one of the critical issues. In order to evaluate the magnetic field homogeneity and the screening-current-induced magnetic field, a 1 T model magnet and some test coils were fabricated. From an evaluation of the 1 T model magnet, it was found that the main reason for magnetic field inhomogeneity was the tolerances in the z-axis positions of the coils, and therefore, it is important to control the gap between the single pancakes. In addition, we have already demonstrated the generation of an 8.27 T central magnetic field at 10 K with a small test coil. The screening-current-induced magnetic field was 0.43 T and was predictable by using an electromagnetic field simulation program. These results were reflected in the design of a conduction-cooled 9.4 T REBCO magnet for whole-body MRI systems. The magnet was composed of six main coils and two active shield coils. The total conductor length was 581 km, and the stored energy was 293 kJ. The field inhomogeneity was 24 ppm peak to peak and 3 ppm volume-root-mean-square (VRMS) for a 500 mm diameter spherical volume (DSV). The axial and radial 5 gauss line locations were less than 5 m and 4.2 m respectively.

Engineering current density over 5 kA mm−2 at 4.2 K, 14 T in thick film REBCO tapes

“…Rare earth barium copper oxide (REBCO) coated conductors (CC) have a tremendous potential for numerous applications such as fusion reactor magnets, high energy particle accelerators, generators, motors, superconducting magnetic energy storage, and magnetic resonance imaging over a broad temperature range of 4-77 K in high magnetic fields of 2-30 T, due to their high critical temperature, high irreversibility field and high critical current density [1][2][3][4][5][6][7][8][9][10]. Several research and development projects are ongoing to develop high-field magnets with insert coils of REBCO, due to its high current carrying capability in high background fields [11][12][13][14].…”

A newly developed screening current simulation method for REBCO pancake coils based on extension of PEEC model

“…In Axi-FEM, currents in the axial component are neglected at the REBCO tape ends. And, it is impossible to consider the spiral pancake-winding structure and the inductive current by the time-varying axial field in (2). However, in [24], Mataira, et al have proposed a method to consider the spiral pancake-winding structure and the no-insulation (NI) winding based on the H-formulation.…”

Current Behaviors of NI REBCO Pancake Coil Wound With Multi-Bundled Conductors During Charging and Against Local Normal-State Transition

“…N recent years, higher magnetic fields are required for higher performance in various fields: medicine (magnetic resonance imaging; MRI) [1]- [3], pharmacy (nuclear magnetic resonance; NMR) [5], particle accelerators [5], [6], and fusion devises [7], [8]. In 2019, it was reported that an insert magnet called "LBC3" wound with Rare-Earth Barium Copper Oxide (REBCO) coated conductor (CC) generated 14.4 T inside a 31.1-T resistive background magnet [9].…”