Keeping HIP treatment in mind, diffusion bonding conditions of 316L-type austenitic steels for a low-temperature damper were investigated. It was found that diffusion bonding of 316L with high-content nitrogen onto 316L with high-content nitrogen was difficult. It was tentatively concluded that the martensite formation near the bonding surface induced during the cooling process was most likely responsible for reducing the bonding strength at -196°C. Complete diffusion bonding properties at -196°C were attained by adopting a combination of 316L with high-content nitrogen and 316L with low-content nitrogen under the following bonding conditions: nitrogen content less than 0.017% in 316L with low-content nitrogen, bonding temperature above 1039°C, surface roughness below 0.07 μm, pressure above 130 MPa and pressing time above 4 h.
Although high-Tc superconductors (HTS) are very promising for high-field generation over 25 T, it is difficult to apply them to NMR magnets because of their low index values and the difficulty caused by superconducting joints. It appears that the present properties of HTS cause poor magnetic-field stability in persistent-mode operation. We applied drift compensation based on flux-pump technology to a 600 MHz NMR magnet that had a poor magnetic-field stability of about -0.7 ppm/h. The drift compensation unit consisted of nested inner (secondary) and outer (primary) coils. The inner coil was connected in series to the main coil circuits, and the outer coil was connected to the auxiliary power supply to sweep the output current very slowly. While the current of the outer coil was changed at an adequate sweep rate by the power supply, a current was induced in the inner coil by inductive coupling. The induced current canceled out the decay of the main coil current that caused by the poor drift of the magnet.