(1) Relationship between Vibration of the Superconducting Coil and Mechanical Heating
      One of the tasks to be tackled in the development of superconducting magnets when adopting simplified ground coils is heating of the superconducting coils during running. The relationship between vibration of the superconducting coils and the resultant heating was therefore examined. In particular, the relationship between yawing vibration of the superconducting coils (which becomes more pronounced when simplified ground coils are adopted) and heat generation was investigated by mechanical oscillation tests independent of electromagnetic influence. A simulated external basin with an incorporated superconducting coil was put into a mechanical oscillation testing device, and the heating value was measured based on helium evaporation when agitated laterally by external hydraulic pressure (Fig. 6). Comparison of the results with heat generation under torsional deformation (the cause of heating in the conventional superconducting coil) showed that heat generation from yawing vibration is significantly smaller than that of torsional vibration at equivalent vibration speeds (Fig. 7). The verification that heat generation by rigid body vibration such as yawing is very small suggests possible reductions in heating of the superconducting magnet compliant with the simplified ground coil during a run.

      A conceptual design of the basic structures such as coil shape was first made, based on the basic specifications of the PLG coil. A prototype of a coil-connecting portion was then built with emphasis on higher reliability through size reduction and the omission of screws (Fig. 9). In addition, endurance tests were performed, including long-term outdoor conduction tests and long-term vibration tests of the coil-connecting portion. The results showed the new design to be safe for use as a ground coil.