Current leads for superconducting magnets have been studied since 1960's. The technology of current leads may seem to have been established both in theory and experiment before the middle of 1970's. Nevertheless, a wide variety of superconducting magnets have been introduced in the last 15 years, and the demands for special current leads have increased in accordance to the variety. A steady advance has been made in the design theory and fabrication of current leads. This paper describes the recent current lead technology regarding the design theory, safety in accidents, and high current capability.
In recent studies of high temperature plasmas, an improvement of plasma confinement properties during auxiliary heating is the most important item. A solid hydrogen-isotope pellet injector is a useful tool for this purpose. This report reviewed a production method of a solid hydrogen-isotope and an acceleration technique of the pellet by pneumatic, electromagnetic and centrifugal forces.
The purpose of this paper is to give an experimental proof of the dynamic stability of face-cooled superconducting tapes presented by one of the authors (T. O). The specimens are made by stacking disk-shape Nb3Sn and stabilizing copper disk alternatively. Stability is estimated by observing flux jumps for specimens of different cooling conditions or different thicknesses of stabilizing copper. The experimental results agree well with the analysis. This work will offer a useful criterion for application of superconducting tapes.
With the stringent requirement from the user community for high-resolution multichannel detectors which cause much heat generation, a future space-borne infrared radiometer on an Earth observation satellite must incorporate a small closed cycle refrigerator instead of the passive radiator which has been used for rejecting heat from small size detectors of satellite radiometers in the past. The Vuilleumier cooler, one such refrigerator, is a heat engine which uses heat energy rather than mechanical energy to cyclically pressurize the working gas. This machine has the potential advantages of long lifetime and low mechanical vibration. This paper first describes the specifications required for the machine, and next the details of design and the test results. As typical specification values, the machine has cooling capacity of 1.5 watts at 80K under input heater power of 150W, charged working gas pressure of 2.5MPa and cycle speed of 4s-1. The limitation of total weight is 6kg. The performance of the machine has been mapped including off-design points. The results show that 1.6 watts was obtained, that the nominal cooling capacity was obtained under the input heater power of 146W, and that 2.2W was the maximum cooling capability. The efficiency as a figure of merit value defined as input power/cooling capacity at 80K was about 135 for cooling capacity of 1W, and 80 for cooling capacity of 2W. It can be concluded that the small Vuilleumier cooler satisfied the preliminary specifications imposed at the beginning.
In recent years, interest in the application of superconductivity to the electric power apparatuses has grown rapidly. In ac power apparatuses, loss induced by alternating current is a impeding problem which has to be reduced. A superconducting power cable is one of the promising ways for transmitting huge electric power efficiently in the future. We have proposed the new ac superconducting cable design with a similar electrical insulation structure to the conventional extruded cross-linked polyethylene cable (CV cable). The feature of this cable is to exploit the excellent electrical insulation capability of polymers at cryogenic temperature by separating helium coolant from the electrical insulation. The conductor of the superconducting cable consists of niobium clad over a copper flat wire and niobium tape, which are wound helically in the opposite direction each other on a copper pipe. In order to clarify the ac loss mechanism in this cable design, measurements and analysis of the ac loss of the superconductor have been carried out at the liquid helium temperature.
Boiling heat transfer characteristics have been experimentally investigated in a channel opened at both ends to a pressurized (1atm) He II bath. Different trends in temperature fluctuation in the channel were observed between the cases when a heat transfer surface is facing upward and downward. This difference in characteristics is considered to be caused by a flow of helium in the channel which is induced by a flow of bubbles. Values of overall heat transfer coefficient between the heat transfer surface and the He II bath indicate a cooling ability of the He II channel quantitatively.
We have successfully developed a technique to control fuel mass loaded in a cryogenic foam target for laser fusion research. An empty cavity is formed inside a spherical shell filled with liquid deuterium by heating the foam shell immersed in liquid deutrium. The foam shell target is then pulled out of the liquid. The liquid deuterium is frozen by increasing flow rate of liquid helium which cools the cryostat and reducing the pressure of surrounding gaseous deuterium. The target is irradiated by the laser beams from Gekko XII laser system. The detailed technique in this method and numerical evaluation on thermal balance in the target are presened.