The upgrade project of the 25T-CSM to 30 T is on-going at HFLSM, IMR, Tohoku University. The goal is to obtain 30 T in a 32 mm warm bore by replacing the present Bi2223 insert coil with one wound using REBCO. In order to develop a robust REBCO high field insert, we adopt a two-tape bundle conductor with a face-to-back configuration. We confirmed that this conductor configuration mitigates effectively the risk posed by local defects in an R&D coil: a stable operation was achieved with negligible degradation in coil I _c even with a severe local defect on one of the two tapes. Quench protection from possible hotspot in the REBCO insert using an early detection method is made possible by the two-tape bundle configuration and the thick Cu stabilizer. Other R&D coils using such conductor were tested with large hoop stresses up to 460 MPa with no degradation. On the basis of these R&D studies, a robust REBCO insert is designed for the upgrade. The designed REBCO insert has a capability to achieve 35 T with enough I _c margin if we accept a maximum hoop stress of 500 MPa.

A superconducting joint and a persistent current switch are the key technologies in persistent current operation for MRI and NMR magnets to obtain higher resolution and sensitivity. We prepared a persistent current system including a superconducting joint, a persistent current switch, and a double pancake coil, which were fabricated with a REBCO tape. The magnetic field decay behavior in persistent current operation were observed in a self-field and the external magnetic field of 1 T at 20 K. In the self-field, the decay rate of persistent current excited up to 170 A reached to 1.7 ppm/h after five days operation. This means that the practical persistent current operation has been achieved successfully using the REBCO superconducting joint. From the voltage-current characteristics estimated from the magnetic field decay, it was found that the decay behavior of persistent current is dominated by the joint resistance in 1 T, but by the shielding current in the self-field.

A 33 T cryogen-free superconducting magnet (33 T-CSM) project is now in progress at HFLSM, IMR, Tohoku University. The 33 T-CSM consists of a φ 68 mm–19 T REBCO (HTS) insert and a φ 320 mm-14 T CuNb/Nb₃Sn and NbTi Rutherford (LTS) magnets. The 33 T-CSM system has been installed and tested without the HTS insert in March 2024. The LTS outsert magnet consists of three CuNb/Nb₃Sn Rutherford cable coils and two NbTi Rutherford cable coils with an epoxy impregnation. It can generate 14 T in a 320 mm bore with 879 A. This winding makes use of advanced high strength CuNb/ Nb₃Sn strands specifically developed for the 33 T-CSM project, enabling high stress design with about 275 MPa in the Nb₃Sn coil at 14 T. The 19 T-HTS insert is designed based on the robust REBCO coil technology we proposed in previous works. For the cooling system, a 9 W GM/JT cryocooler is used for the LTS coils, four 4 K-GM cryocoolers cool the REBCO coils (1.5 W each at 4.2 K) and two single-stage cryocoolers are used for the radiation shield and current leads. Helium circulation with compressors ensure the thermal connection between the coils and the cryocoolers. The initial cooling is about 7.3 days from room temperature. The test of the 14 T LTS magnet was successfully completed up to 839 A with the nominal maximum electromagnetic stress of 275 MPa after one training quench.

Magnetic field stability and hysteresis can be serious problems in a high-field high-temperature superconducting magnet, because of the large shielding current effect. Accordingly, the field stability of a 25 T cryogen-free superconducting magnet (25T-CSM) was investigated. This particular system can generate a central field of 24.6 T in a 52-mm room-temperature bore. It was found that the magnetic field relaxation rate of the 25T-CSM with a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _y (Bi2223) insert was due to the flux creep effect, and was small enough to allow nuclear magnetic resonance (NMR) experiments. Based on these experiences in the development of the 25T-CSM, primitive designs for a 30 T cryogen-free superconducting magnet (30T-CSM) were suggested based on upgrading the present Bi2223 insert to a REBa ₂ Cu ₃ O _y (RE123, RE: rare earth and Yttrium) insert incorporating two co-wound RE123 tapes. It was confirmed that the prototype test coil could be operated at 4.2 K under large electromagnetic stresses of up to 540 MPa without experiencing degradation.

Poly-l-lactic acid (PLLA) has biocompatibility and unique characteristics such as piezoelectric properties. This attracts attention not only in the environmental field but also in the biomedical and electronic materials fields. In recent years, the literature about orienting PLLA crystals has been promoting new applications for PLLA such as high strength fiberization and piezoelectric properties. This paper presents a new technique to orient the PLLA crystalline through casting under magnetic irradiation. The advantage of this technique is that it is possible to radiate the magnetic field to the PLLA crystalline in an extremely low viscosity environment. Moreover, the heat treatment condition was optimized in order to improve the low crystallinity of casting, and it succeeded in producing a PLLA film with a high degree of orientation and high crystallinity. Furthermore, PLLA/1-butyl-3-methylimidazolium dibutylphosphate (bmimjdbp) composite films were prepared under the same conditions, and this also succeeded in the further improvement of crystallinity.

The upgrade to 30 T of the existing 25 T cryogen-free magnet (25 T CSM) at the High Field Laboratory for Superconducting Materials, Tohoku Univ., will consist in replacing the existing High Temperature Superconductor insert made of Bi-2223 by one wound using REBCO tape. The new insert is designed to produce 16 T instead of 11 T. In order to have good dynamics and allow sweeping mode experiment, the insert will be conventionally isolated, as it was the case for the previous Bi-2223 version. In previous work we modelled thermal runaway phenomenon and showed that a sensitive dissipative voltage detection technique can give sufficient warning to protect an HTS coil using external dump resistor even in the case of sharp local critical current drop. For the 30 T insert, the conductor will consist of a two tape bundle so as to reduce the chance of such sharp Ic drop due to tape performances inhomogeneities or local damage. We simulate the quench dynamics in the LTS outsert coupled with the HTS insert to demonstrate that the existing detection/protection system of the 25 T CSM can be re-used and determine the current dumping dynamics. We then use our thermal runaway modelling tool to study the behavior of the future 16 T REBCO insert in case of local sharp defect and determine realistic detection threshold for its safe protection.