The preparation of superconducting generator has been in steady progress, the construction of 70MW model machine has been carried on as planned in the NEW SUNSHINE PROJECT. The R & D of NbTi field windings is the key technology, and the test codes has been developed. It is necessary to standardize the evaluation of superconductors used in generators. The test codes of NbTi superconductors has been considered. The following test codes have been developed to standardize the test methods; (1) pretreatment of sample, (2) form of sample, (3) test conditions, (4) test method, and (5) analyzation of test results. This paper will show an outline of the test codes and several analyzed results in 70MW generator.
In the present paper we have investigated the method to produce the high efficient regenerator by using the magnetic regenerator materials in the He temperature range. These days, the magnetic materials with low magnetic phase transition temperature Tc are thought to be the promising regenerator materials below 10K. However, the very sharp peak of the magnetic specific heat CJ appears near Tc in the temperature dependence curve and, moreover, its value is almost same order of the value of the specific heat of the He gas. Therefore, it is difficult to make the efficient regenerator by using only a kind of a magnetic material. In the present investigation, in order to produce the highly efficient regenerator, we selected two kinds of magnetic materials whose Tc's are different, and produced the layered type regenerator in which the magnetic material with the high Tc piled up that with the low Tc. In the computer simulation and experiment it is verified that the layered type regenerator (Er0.9Yb0.1Ni+Er3Ni) is more efficient than that with only Er3Ni. Moreover, we have made new double-layered regenerator with Er0.9Yb0.1Ni and Er3Co, where Tc of Er3Co is almost twice Tc of Er3Ni. Applying this regenerator to the GM refrigerator, we have succeeded to obtain the fairly large refrigeration capacity of 1.05W at 4.2K. Finally, on the basis of the above results, we discussed the direction of the development of the magnetic regenerator in future.
On the development of the superconducting helical coil, it is important to examine the mechanical behavior of the coil and the evaluation of the coil rigidity at liquid helium temperature. The helical coils in the Large Helical Device are subjected to high electromagnetic force of about 10MN/m. This paper deals with the mechanical behavior and the compressive rigidity of the superconducting coil pack under compressive load at liquid helium temperature. Finite element method is used for the numerical analysis of the composite structure of the coil pack. The numerical results of displacements and strains are obtained and compared with the experimental results. The validity of numerical techniques for evaluating the rigidity of the coil pack is also examined.
Field operation and cooling test of high Tc coil made of Bi-based pancake coil were carried out. By the measurement of critical current distribution inside the high Tc coil, we found that the critical current of the edge pancake coil is lower than that of the center pancake coil. This result is explained quantitatively in consideration of field and field angle dependence of critical current for the tape-shaped conductor and field distribution inside the coil. Magnet system assembled GM-refrigerator, high Tc current lead and the high Tc coil was tested. As a result, it was found that thermal load into the coil was low and field operation up to 90% of critical current of the high Tc coil was stable.