Recent instruments for the celestial far-infrared observations are reviewed with some examples. They are loaded on airplanes, balloons, rockets, and satellites because of the atmospheric absorption and emission. Furthermore, some of these are cooled down below 10 degree K by liquid helium cryogen to be free from the thermal radiation noise generated by warm instruments, for example, mirrors, filters. IRAS, which is a cooled and satellite-borne telescope, had been able to detect the extremely weak far-infrared radiation from many celestial objects. It was demonstrated by IRAS that the cryogenic technique is indispensable for the far-infrared observation of high sensitivity.
Large superconducting solenoid magnets are used in high energy physics experiments with colliding beam accelerators. Since solenoids are surrounded with other detectors, they are required to be thin in terms of radiation length in order for particles produced by interactions to pass through the coils with minimal absorption. Various techniques have been developed for construction of large, thin superconducting solenoids. First, heavier materials of solenoid components are substituted by lighter materials of aluminum alloys. Second, the forced flow cooling method of two-phase helium is applied since the pool cooling requires a substantially thicker cryostat arrangement. Since such solenoids are not cryogenically stable and since they hold large stored magnetic energies of about 10×106J or more, it is essential to make them intrinsically safe against quenches. The CELLO solenoid used pure aluminum as the stabilizer of the NbTi/Cu superconductor, while the TPC solenoid used the conductive bore tube for diverting the magnetic current from the superconducting coil to protect the coil against quenches. The CELLO-type aluminum stabilized conductor can be fabricated intrinsically stable and it has the advantage that the maximum voltage and temperature at the coil during quenches can be easily controlled by optimizing the amount of aluminum stabilizer. The aluminum-stabilized NbTi/Cu superconductor with the EFT method is used in the CDF solenoid (3mφ×5m, 1.5T, 30×106J). Two solenoids for TRISTAN experiments (TOPAZ and VENUS) also use conductors fabricated essentially with the same method as in the CDF solenoid. All the three solenoids do not possess permanent inner bobbins in order to reduce the coil material thickness. The shrink-fit method is used for the CDF solenoid, while the inner winding method is used for the TOPAZ solenoid. Various technical difficulties with construction of large, thin superconducting solenoids will be described.
Measurements of length change in glass-cloth laminates FRP insulator of superconducting magnets for fusion reactors were made after reactor irradiation at 5K in directions both parallel and perpendicular to the fibre axis and during subsequent annealings in the temperature range of 10-320K. Measurements of the length change were carried out by changes in capacity using a ac ratio bridge. The fractional changes of length induced from the irradiation in the direction perpendicular to the fibre axis Δl/l was estimated to be 2.3×10-3 for a dose of 4.5×108 Rad and this corresponds to about 40 times larger than that of pure Al after reactor irradiation at 5K and also to 70% magnitude of thermal contraction of pure copper between room temperature and 4.2K. A small recovery of length change in the direction parallel to the fibre axis below 100K was followed by a large recovery around 200K. Reverse recovery of the length change in the direction perpendicular to the fibre axis was found above 200K. When those insulators are exposed by the irradiation under the operating condition of the superconducting magnet for fusion reactor, they experience two kinds of stress, one is due to the magnetic field itself and the other to the effect of the irradiation. The length change introduced by the irradiation will give rise to mechanical disturbances, for example, slip, debond and crack, and to deleterious changes in the engineering properties of the magnet. These disturbances due to length change in the insulator and the reverse recovery of length change are discussed.
The High Field Laboratory for Superconducting Materials was established in April 1981 at Tohoku University in order to provide research facilities for the development of superconducting materials suitable for superconducting magnets for the plasma confinement in fusion reactors. Main facilities of this laboratory are three hybrid magnets up to 30 Tesla dc magnetic fields with inner bores from 32 to 52mm in diameter. The magnets consist of superconducting outer solenoids and water-cooled inner ones with a maximum steady power dissipation of 8MW. The design and construction of these three hybrid magnets have finished in last three years, and two of them (HM-3; 20T, 32mm bore and HM-2; 23T, 52mm bore) have already opened to scientists and engineers in the superconductivity and other fields. The rated field of the third hybrid magnet (HM-1) is 31 (or 29) Tesla in a bore of 32 (or 52)mm in diameter. By this hybrid system we have succeeded to produce 29.3 Tesla on April 21, 1984. Detailed descriptions are presented on the superconducting magnets, power supplies and cooling systems for them, water-cooled magnets, dc-high power source and water-cooled system for them, the monitoring and control system for the hybrid magnets including a super-minicomputer system, a hard-wired interlock system for the safety of human beings and machines, and so on. The fourth hybrid magnet system which aims at 35 Tesla as the next phase is also discussed.