Present status of a pressurized superfluid helium cooling and its related high field superconducting magnet is reviewed. The research and development of high field superconducting magnets employing multifilamentary superconducting wires have been performed so far. NbTi alloy and Nb3Sn compound superconducting wires have indicated their own properties enough to be high field superconductors and have been practically applied for high field superconducting magnets. In order to construct high field superconducting magnets, the optimization of a coil structure which enables us to stand a huge electromagnetic force and effectively to generate a magnetic field is needed. It is desired that the pressurized superfluid helium cooling will contribute to the optimization of superconducting magnets and will improve their performances in high fields.
There is presently an urgent need in space cryogenics for the development of highly efficient and reliable, and light weight cooling systems as well as the development of high performance heat pipes and radiation heat rejection systems. This article describes infrared sensors and cooling system requirements, and representative cryocooler systems developed since the 1970's for on board satellite use.
The development and applications of high resolution magnet system in National Research Institute for Metals are reported. The high resolution magnet system consists of three different sub-systems to cover various types of experiments under high resolution magnetic fields. The three sub-systems are designed for the detection of the quantum oscillations, for broad band solid state NMR experiments and for high resolution solid state NMR experiments, respectively. The purpose and specifications of each sub-system are described together with a brief introduction to each experiment. Typical examples of applications such as the de Haas-van Alphen effect of heavy Fermion compound UGe2, broad band solid state NMR of high Tc oxide and high resolution solid state NMR of 17O in Glycine are given to demonstrate the potentiality of the sub-systems.
We are now developing a 70MW class superconducting generator with low response excitation (hereafter we call it simply 70MW class machine). The field windings for the 70MW class machine require high current density to achieve low reactance and low a. c. losses to resist the magnetic flux variation at the power system fault. To develop such field windings with high current density and low a. c. losses, it is important to select proper superconducting cables and to find appropriate cable supporting and cooling system. Therefor we constructed model coils of the field windings for the 70MW class machine and investigated these performance. This paper describes at first the configuration of the model coils and then the test apparatus and the test method for these model coils. This paper also describes the test results and the applicability of these test results to the field windings for the 70MW class machine. We have found the superconducting cable and the cable supporting and cooling system which are applicable to the field windings for the 70MW class machine.
In the present paper, a model for the temperature take-off condition of superconductors cooled in a liquid coolant is presented to estimate the maximum operating current and allowable thermal disturbance in the critical current-margin design criterion for high performance magnet stability. In the model, the take-off time of conductor temperature is estimated as the sum of transient heat conduction and macrolayer evaporation periods. The former is estimated by a transient heat conduction analysis and an activation criterion of pre-existing nuclei. To estimate the latter, the macrolayer model proposed by Haramura and Katto for steady-state critical heat flux is extended to transient states. Prediction from the present model is in good agreement with the experimental data of the take-off time.
Oscillating motions of inviscid fluid are discussed using linearized forms of Euler and continuity equations. Differential equations for the spatial variations of pressure and displacement become simple at a limit of small wave-number. At this limit some methods of calculating distributions of temperature, energy fluxes, displacement amplitudes and phase are discussed using these equations and results of semilocal thermoacoustic theory. Examples of numerical calculations are given for a regenerator of refrigerator and for a basic pulse tube. Results of the calculations are so satisfactory that this method of calculation is going to be a tool for better understanding of thermoacoustic phenomena and for developing devices associated with oscillationg fluid.
New types of oil free Helium refrigerators, using centrifugal compressors are now under development to cool the superconducting electric power generators. Because of their low efficiency, not much attention has been paid to regenerative compressors up to now. But, their compression characteristics, for example, higher pressure ratio and no surging vibrations, are desirable for Helium refrigerators which require perfect reliability for cooling practical superconducting machines. This report describes the merits expected by adaption of regenerative compressors to new type Helium refrigerators, construction of the trial compressor equipped with 5-axis controlled magnetic bearings and results of the basic test operation of the magnetic bearings.
A theoretical and experimental study on the mechanical behavior of the coil structure of a superconducting magnet have been performed to evaluate the coil rigidity. A two-dimensional finite element analysis of the composite structure is used to interpret the experimental results. It was found that the sample coil received the bending moments, so the bending effect should be considered. The validity and limitations of analytical and numerical techniques for evaluating the coil rigidity was examined.
In order to discuss energy flows in a regenerator, distributions of temperature, energy flows, amplitude of displacement and phase angle are calculated using thermoacoustic theory of inviscid fluid. Although function of the regenerator varies depending on the phase at the cold end, the regenerator behaves as a converter between heat and work flows. Enthalpy flow for the refrigeration mode is a part of energy flow, which remains unconverted, and it corresponds to regenerator loss. Regarding the regenerator as an amplifier of energy flows, the regenerator of work-amplifier mode amplifies work-flow by using heat flowing in at the hot end as an energy source. The amplification coefficient is smaller than a ratio of temperature at the hot end to one at the cold end, TH/Tc. The regenerator of refrigeration mode amplifies heat flow by using work flowing in at the hot end as an energy source. The amplification coefficient is larger than TH/Tc. Regarding the regenerator as a converter of energy flows, it converts work flow to heat flow of the inverse direction for the refrigeration mode, and it converts heat flow to work flow for the work-amplifier mode and the self-sustained oscillation mode. Efficiencies of these conversions are COP of the regenerator for the refrigeration mode and thermodynamic efficiency of the regenerator for the work-amplifier mode and the self-sustained oscillation one.
The authors have been studying the fabrication conditions of long silver-sheathed Tl-series oxide superconducting wires. A multi-layered pancake coil was fabricated by piling 12 single pancake coils wound with the 17.5m long tape shaped wires. It was confirmed by the criterion of 10-13Ωm that the multi-layered pancake coil was superconducting on the whole length. This multi-layered coil generated a maximum magnetic field of 510G at 77K and 1, 410G at 4.2K, respectively. The Jc of this coil was restricted by the local Jc properties of the tape where the maximum self-magnetic field of the coil was induced.