Superconducting magnets have become essential components of large accelerators/colliders. Their technology has greatly progressed because of the production of Tevatron, HERA, and RHIC magnets and the intense R&D programs for SSC and LHC. In KEK superconducting quadrupole magnets, which are the first superconducting accelerator magnets in Japan, were developed in the 1980s and installed into the interaction regions of the TRISTAN collider. Since commissioned in February 1991, the magnets had operated five years without serious trouble and contributed to double the luminosity. This paper describes the features and the construction history of the magnet systems.
In the Engineering Design Activities of the International Thermonuclear Experimental Reactor (ITER), a Central Solenoid Model Coil (CSMC) and a CS Insert Coil (CSIC) have been tested successfully. The CSIC conductor consists of 1, 152 superconducting strands bundled on a central cooling channel. As interesting phenomena in the CSIC experiment, it was observed that a pressure drop of the CSIC decreased by about 12% during a current-carrying operation at 40kA, and coupling losses indicated an operating current dependence. It is considered as a hypothesis that an electromagnetic force causes a compressive deformation of superconducting cable in a jacket and that a new flow path was then generated between cable and jacket. Therefore it is also considered that the decreasing of contact resistance between strands as a result of the electromagnetic force derives an increase of coupling losses in the conductor. A pressure drop calculation model with a gap generated by electromagnetic force is constructed. The gap is estimated to be about 1.4mm at nominal operating conditions (13T, 44.3kA). From this calculation, a void fraction as a function of electromagnetic force is evaluated during the current-carrying operation of CSIC. The coupling time constant (nτc) as a function of void fraction is then calculated from the coupling loss measurement result during the pulsed operation of CSMC and CSIC. The evaluated nτc is about 24ms and is close to nτc of 20-30ms of a heat treated short sample having a history of exposure to the electromagnetic force. We used the evaluated nτc as a function of electromagnetic force to calculate the coupling losses, which varied from 24ms to about 50ms during pulsed current operation. These results show a good agreement with measured coupling losses, depending on coil current. To reduce the possibility of strand damage as a result of cable movement, we also here proposed that the void fraction of real ITER conductor should be smaller than that of CSIC, and it is preferable that the void fraction is about 34.5%. In this paper, the quantitative explanation of coupling loss change under the electromagnetic force is described from the viewpoint of the pressure drop change.
This paper describes the results of a visualization study of the phase transition process and heat transport phenomenon in supercritical air near the maxcondentherm point. The phase transition from the vapor/liquid equilibrium state to the supercritical state is observed by the use of a shadowgraph technique. On the other hand, the heat transport phenomenon in supercritical air is investigated by the use of a laser holographic interferometer. The initial temperature gradient, which suppresses the generation of convection, is made in the experiment, and heat is applied in step functions from the planar heater. We can successfully observe the heat transport phenomenon in supercritical air, and the experimental results are compared with that of supercritical nitrogen, We report the difference of the heat transport phenomenon between the supercritical air and the supercritical nitrogen.
Although protein crystals of high integrity in a microgravity environment have been reported, the actual implementation of these experiments are very limited. The use of magnetic force is among the most promising methods of simulating the virtual microgravity environment on earth. We have been carrying out the development of superconducting magnets for generating uniform magnetic force fields since 1997. It was not clear at the beginning of this study what configuration of superconducting coils could generate high and uniform magnetic force fields most effectively. We used a nonlinear programming method to reach an optimized design. We constructed a superconducting magnet for generating uniform magnetic force fields, whose coil parameters were based on the optimization result. The superconducting magnet was wound with NbTi conductors and designed to generate 240T2/m of the magnetic force field and 9T of the central magnetic field. This magnetic force field can cancel 17% of the gravity force for pure water. The variation of the magnetic force field is less than 1.0% in the axial component and less than 2.0% in the radial component. The uniformity of the axial component was experimentally confirmed. The magnet has now been in operation for protein crystal growth experiments.