The IRTS (Infrared Telescope in Space) was launched on March 18th UT by the H-II rocket as a part of the Space Flyer Unit (SFU), which is a re-usable free flyer designed as a multi-purpose common facility for scientific and engineering experiments. The IRTS, cooled by He II at 1.91K, had successfully completed the whole infrared astronomical observation mission for 37 days, and every detector for the observation in the whole infrared region worked quite satisfactorily. A tremendous amount of observation data was obtained which is now being analyzed. On January 27th, 1996, the SFU was retrieved by a US Space Shuttle. In this report, the flight data of the thermal performance of the cryogenic system is discussed and the development of the IRTS is also briefly described.
Both high critical current densities and low hysteresis-losses are needed for Nb3Sn strands used for poloidal coils in a nuclear fusion experimental reactor. Since our internal-tin route Nb3Sn wires have many advantages except for hysteresis-loss, it is important to improve the loss immediately. The reason why the loss gets large with our internal-tin process is pointed out to be the bridging of filaments with one another. Hence, it is necessary to elucidate the growth mechanism of the bridging by all means in order to greatly decrease the loss. We investigated the mechanism through the cross-sectional observations and analyses of the wires at each step in an annealing pattern. According to the results, we found out that the mechanism was based on the phenomena that Cu matrix near the boundary of ε-phase bronze was lost in the pre-annealing at 450°C. As a result, the filaments in that region were approaching each other, finally leading to the occurrence of bridging. The phenomena of the disappearance of Cu matrix and the movements of the filaments were able to be explained consistently from the different diffusion rate between Cu and Sn.
Both high critical current densities and low hysteresis-losses are needed for Nb3Sn strands used for poloidal coils in a nuclear fusion experimental reactor. It is important for our internaltin route Nb3Sn wires to improve the loss immediately. Recently, we have successfully elucidated the growth mechanism of the bridging, which was the cause of generating the large losses in the internal-tin processed wires. Hence, we tried to improve the loss by means of re-forming the wire construction based on the mechanism. The bridging was completely suppressed by decreasing the diameter of the tin core to 82% and the losses in those wires were decreased to 172-193kJ/m3, which corresponded to 66-59%, comparing with one in a conventional wire. Furthermore, good agreement between estimations from a calculation and actual cross-sectional observations was obtained at the growth position of the bridging, by which we could verify the hypothesis of the growth mechanism of the bridging.
Understanding of basic physical properties of oxide superconductors is very important for the development of electric power apparatus. A lot of studies have been mainly carried out with DC or AC. However, the frequency dependence of physical properties of oxide superconductors seems not to have been reported except for AC loss. In the present study, a power source was constructed which can supply 10A up to 150kHz. The frequency dependence of the quenching current of bulk and thin-film oxide superconductors was measured using this power source. The results are discussed in terms of heat balance between generation due to hysteresis loss and dissipation to coolant.