Magnetic Field Stability Control of HTS-MRI Magnet by Use of Highly Stabilized Power Supply

Low-temperature superconducting MRI magnets are usually cooled by a large amount of liquid helium (LHe); however, LHe is getting scarcer and its price has been rising. Therefore, the development of helium free high-temperature superconducting (HTS)-MRI magnet is expected. HTS-MRI magnet fabricated by REBCO tape superconductors has mainly two problems for producing a highly stabilized magnetic field for MRI imaging. One problem is current fluctuation of a power supply, which is necessary for excitation because the permanent current operation of HTS-MRI magnet is difficult. Another is a screening current in REBCO tapes, which affect the magnetic field stability. The MRI magnetic field feedback control test was carried out, that is, the overshooting and the current feedback control, using 32 H HTS-MRI test magnet and the highly stabilized power supply. The magnetic field was evaluated under the current feedback control at 1.5 T (66 A). By the overshooting and the current feedback control, the magnetic field stability was improved to 0.7 ppm/ h which is enough for MRI imaging.