Hideto Yoshimura

Helium Liquefaction by a Gifford-Mcmahon Cycle Cryocooler

This paper describes the principal design features and performance test results of a three-stage Gifford-McMahon cycle cryocooler by which the authors have achieved no-load temperature of 3.3 K and succeeded in helium liquefaction. The key point of the success is the selection of GdχEr1-χRh compounds as a regenerator material. The refrigeration capacity was 20 mW at 4.2 K and the helium liquefaction rate was 10 cm3/h. This is the first success that a Gifford-McMahon cycle cryocooler has liquefied helium without precooling.

Helium liquefaction by a Gifford-McMahon cycle cryogenic refrigerator

This article describes the principal design features and performance test results of a three‐stage Gifford–McMahon cycle cryogenic refrigerator by which the authors have achieved a no‐load temperature of 3.3 K and succeeded in helium liquefaction. The refrigeration capacity was 20 mW at 4.2 K and the helium liquefaction rate was 10 cm3/h. The key point of the success is the selection of GdxEr1−xRh compounds as a regenerator material. This is the first time that a Gifford–McMahon refrigerator has liquefied helium without the use of a Joule–Thomson stage.

Large aperture superconducting magnet (benkei)

Abstract Benkei, which was a large window frame conventional magnet at KEK has been converted to a superconducting magnet. In the conversion, the pole gap has been doubled from 0.5 m to 1.0 m retaining an analysing power at 2 T m. Several new techniques were applied to coil windings and cryostat fabrication. The superconducting Benkei has shown satisfactory performances for long term operation.

Design parameters influencing non-uniform current distributions in superconducting multi-stage stranded cables

We have suggested that non-uniform currents occur due to certain design parameters, for example a combination of cabling pitches, in a previous study. In the present study, we evaluate the occurrences of non-uniform current distributions in terms of design parameters, i.e., the combination of cabling pitches, winding methods (solenoidal and pancake winding) and cross-sectional shape of the cable by numerical analyses. Finally, some basic design concepts to solve this problem are proposed.

4K Three-Stage Gifford-McMahon Cycle Refrigerator for MRI Magnet

The authors have succeeded in the development of a 4K Gifford- McMahon cycle cryogenic refrigerator capable of eliminating the evaporation of helium from a superconducting MRI magnet. We installed this refrigerator in a superconducting MRI magnet and established that it actually eliminated evaporation and was capable of stable operation.

Normal propagation velocity and quench energy of the rotor model for a 70 MW class superconducting generator

A rotor model was fabricated to estimate the performance of the 70 MW class superconducting generator. The normal propagation velocity and quench energy for the rotor model in the rotational field are measured at various rotating speeds. An analytical model is proposed in order to explain the experimental data. In the calculation, the heat transfer and the temperature rise of liquid helium in the rotational field are considered. The calculated results are compared with the experimental data, and these agree well. Therefore it becomes possible to precisely design field windings of superconducting generator.

A 30 L/H HELIUM LIQUEFIER FOR A 30 MVA SUPERCONDUCTING SYNCHRONOUS CONDENSER

A 30 1/h helium liquefier for use in a 30 MVA superconducting synchronous condenser has been developed, and successfully tested in combination with a 6 MVA superconducting synchronous generator which had been previously developed and installed at MELC0 Central Research Laboratory. A 30 MVA superconducting synchronous condenser has already been installed and is going to be tested in combination with the 30 1/h helium liquefier. The principal design features of the liquefier are described and the test results are presented.

Numerical analyses for ramp rate limitation from the standpoint of heat generation during current redistribution [in superconducting cables]

The ramp rate limitation (RRL) must be improved for large applications, for instance fusion machines. In superconducting multi-strand cables, adding to the coupling loss, the heat generation during current redistribution (moderation of a nonuniform current) causes temperature rises. Especially for cables in conduit-type conductors (CICC), the relation between the heat capacity of the coolant and the total heat dissipation determines the temperature rise. When this rises above the current sharing temperature, the conductor must quench. To establish stability against nonuniform current distribution, a small contact resistance between strands is preferable. However a smaller contact resistance results in a larger inter-strand coupling loss. Therefore, the contact resistance must be optimally designed to prevent the cable from RRL. In this study, the authors analyzed the current redistribution in a three-strand cable with electrical contact between strands. The heat generation due to: (1) normal resistance; (2) contact resistance between strands; and (3) terminal joint resistance were evaluated in the cases of a variety of contact resistances and cooling conditions. Finally, some of the particular phenomena reported as being found in experiments with multi-strand cables were simulated by analyses and then discussed.

Thermofluid Analysis of Shuttle Loss on Regenerative Cryocoolers

Shuttle loss is one of major losses of regenerative cryocoolers. In order to improve the efficiency of the cryocoolers, we have to estimate the shuttle loss precisely and reduce it. However, it has been difficult to calculate shuttle loss precisely because the hydrodynamic behavior of the working fluid has not been considered in the analyses and the temperature gradient of the working fluid was given as linear. Therefore, using a general purpose thermofluid analysis software STAR-CD1, we made a model in which the hydrodynamic behavior of the working fluid was considered. By using this model we did a thermofluid analysis which calculated the movement of the working fluid and the temperature change. From this, we calculated the shuttle loss. As a result of these calculations, the preciseness of the calculation model was confirmed by comparing with previous analyses. This means that acceptable analysis is possible with general purpose software, and various models. This paper reports on the analysis model and the results.

A Conceptual Design of a Superconducting Magnet for a Magnetic Levitated Train Using a High Tc Oxide Superconducting Wire

A conceptual design of a superconducting magnet for magnetic levitated train (MAGLEV) using a silver sheathed wire of high Tc oxide superconductor is studied. In the conceptual design, the superconducting magnet is operated by persistent current at 20K. The efficiency and the reliability of refrigerator are high at 20K. The critical current density of 6x104 A/cm2 is required at 5T for the conductor. The coil is stable against disturbance, because the minimum quench energy is large. On the other hand, the quench propagation velocity of the coil is low. The coil needs active quench protection.