Effect on temperature dependence for long-term stable control of the magnetic field at sub-ppm using superconducting magnet for MRI

Sugita, Moe ; Abe, Mitsushi*; Iinuma, Hiromi*; Ogane, Chiori; Ogitsu, Toru*; Sasaki, Kenichi*; Mibe, Tsutomu*; Shimomura, Koichiro*

The MuSEUM experiment at J-PARC requires a long-term stability of less than 0.2 ppm time variation of magnetic field and less than 0.2 ppm (p-p) homogeneity for the ellipsoidal region of 20 cm in diameter and 30 cm in length. The superconducting magnet used in the MuSEUM experiment takes a method of shimming to adjust homogeneity by placing iron shims. The factors changing magnetic field with temperature is considered the location shift of shims due to the thermal expansion of the shimming structures and the temperature dependence of iron magnetization. Therefore, the magnetic field was measured during heating the shimming structure, and the temperature dependence of magnetic field was confirmed. In addition, location-shift and magnetization change were calculated by simulation. Based on the measurement and simulation results, it is necessary to control the room temperature within 0.2 K to keep long-term stability in the current experimental system.