At present, National Space Development Agency of Japan (NASDA) is moving ahead of the development tests of the cryogenic engine LE-5, and setting further about the development of the second-generation, high-performance rocket engine LE-7.
Combination of liquid oxygen (LOX) and liquid hydrogen (LH₂) was chosen as propellants through the technological experiences of LE-5, to minimize the total vehicle weight for certain launching capacity into geostationary orbit.
The most critical point to realize this high-performance engine is in the high pressure level, especially the turbopump discharge pressure must be increased remarkably.
This paper concentrates on LE-7 LH₂ turbopump and introduce followings.
1) Required performance and Restraints for LH₂ turbopump
2) Description of design
3) Technical problems

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A bronze-processed Nb₃Sn wire with a Nb barrier protecting Cu stabilizer from Sn diffusion contains a superconducting hollow cylindrical layer of Nb₃Sn inside the barrier. Moreover a Nb₃Sn superconducting layer in each filament is hollow cylindrical, too. In this paper the expressions for the magnetizations and hysteresis losses for this type of wire were derived in the case where a transverse AC magnetic field of trapezoidal wave form with a small amplitude was superposed to a DC bias magnetic field. The present expressions were compared with our experimental results and both of them agreed well with each other over a wide range of the DC bias field.
The hysteresis losses of a Nb₃Sn wire with a Nb barrier is mainly subjected to the magnetizations of a superconducting cylinder inside the Nb barrier, and amounts to several times larger than that with a Ta barrier. It is also pointed out that the values of critical current densities of superconducting barrier and superconducting filaments which contribute to the magnetization are usually different from that estimated from the critical current measurement by a resistive method, while the magnetic field dependences are nearly the same.

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A theoretical expression for the hysteresis loss in a transverse AC magnetic field with a large amplitude of trapezoidal wave form is derived for a bronze-processed Nb₃Sn multifilamentary superconducting wire with a Nb barrier protecting Cu stabilizer from Sn diffusion.
The present expression shows a quantitative agreement with our observed results over the whole range of the amplitude of the applied AC magnetic field up to near H_c2. It is to be emphasized that the values of pinning parameters adopted to estimate the values of hysteresis losses are the same as used in our previous paper to explain quantitatively the hysteresis losses when an AC magnetic field of a small amplitude is superposed to a DC bias magnetic field. Hence the hysteresis losses of a bronze-processed Nb₃Sn multifilamentary superconducting wire with a Nb barrier can be described systematically over the whole range of the magnetic field by means of the modified Irie-Yamafuji model for the critical current density, if we take into account that the value of the critical current density contributing to the magnetization is usually larger than that estimated from resistive measurements.
It is also pointed out that the theoretical expressions for the hysteresis losses used frequently so far give rise to smaller values than the present expressions by a factor of more than 2, and are not adequate for a quantitative description of the hysteresis losses.
The present expressions for the hysteresis losses can also be applied to a bronze-processed Nb₃Sn multifilamentary superconducting wire with a Ta barrier in which any superconducting layer is not produced.

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Effects of a tin-diffusion barrier on the coupling current loss was investigated for a bronze-processed Nb₃Sn multifilamentary composite, and a general expression for the coupling current loss was derived for the composite with several normal-conductor jackets subjected to a transverse magnetic field with a trapezoidal wave form of a practical sweep rate.
In a low frequency range, the present expression is reduced to the one presented previously by authors et al., where the ratio of the coupling current loss between the cases of a Nb and a Ta barrier is equal to the ratio between the effective coupling time constants τ_eff's for the corresponding cases. It was shown that the saturation tendency of the increment of the coupling current loss with the increase of the sweep rate begins at remarkably small value of the sweep rate within the practically used range, especially for the case of composite with the tin-diffusion barrier made of Nb. The present theoretical results were compared with our observed data for both cases of Nb and Ta barriers, and the agreement between them seems to be fairly satisfactory.

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Thermally stimulated current (T. S. C.) and dielectric loss (D. L.) measurements have been performed on five kinds of commercially available organic composite materials, such as G-10CR^R, G-11CR^R, Spaulrad^R, Lamiverre-A^R, and Hoxan^R. Substantial information on the changes and degradation in matrices was obtained from both measurements. The different temperature dependences of T. S. C. and/or D. L. were revealed in differnt matrices of FRP. Further T. S. C. and D. L. measurements were also performed on the specimens which were subjected to different curing conditions or gamma irradiation up to 2.1×10⁹rad. Long curing time resulted in a decrement of the magnitude of T. S. C. Higher gamma doses induced enhancements of T. S. C. Inter laminar shear strength of irradiated samples was decreased by 25 per cent in comparison with that before irradiation. This decrement in irradiated samples was discussed on the basis of the results from T. S. C. measurements. It was found that T. S. C. and/or D. L. measurements supplied significant information on the change in characteristics and degradation of organic composite materials.

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The physical and mechanical properties of GFRP at cryogenic temperatures have been studied for designing a large-sized GFRP dewar. As mechanical properties, the impact strength and the tensile strength have been investigated. From the results, it is shown that GFRP is not brittle at cryogenic temperatures, and the tensile strength increases with decreasing temperature. Therefore, it is adequate as a structural material at cryogenic temperatures. Anisotropy of tensile strength of the GFRP is so large that it has to be taken into account when GFRP is used as a structural material of the large-sized dewar. As thermal property, the thermal contraction has been investigated. The results show that the thermal contraction depends on the glass content and fiber direction. This anisotropy has to be taken into account for designing the dewar.

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In order to meet the prospective application of a GFRP dewar for energy storage system using a large superconducting magnet, the dewar with a complex structure together with a large size are desired to be made. It is difficult to manufacture such a type of the dewars in one united body. These dewars can be manufactured by the adhesive-bonding method. In the present study, the mechanical strength of adhesive-bonding is studied from this point of view.
The mechanical strength of the adhesive-bonding has been investigated by the static tensile method and the impact loading method using small test samples. The results obtained from these tests are important to design the GFRP dewar.
From the static tensile tests, the following results have been obtained. For the sample adhesive-bonded with insertion structure, the mechanical strength of the adhesive-bonding is found to depend on the adhesives used and on the difference of the thermal contraction between the materials which are adhesive-bonded each other. Using a soft adhesive as Araldite 106, the mechanical strength of the adhesive-bonding is small at room temperature, but it remarkably increases at cryogenic temperatures. For a hard adhesive as Araldite 103 and Stycast 2850FT, it is large at room temperature, and it further increases at cryogenic temperatures. The dewar has to be strong enough not only at cryogenic temperatures but also at room temperature. A soft adhesive is not suitable for constructing the dewar. For the sample adhesive-bonded with screwing structure, the mechanical strength of the adhesive-bonding depends on the shear strength of GFRP itself. The mechanical strength of the adhesive-bonded part increases with the decreasing temperature. Therefore, this screwing method is advantageous for the construction of the dewar.
According to the impact loading tests, it is found that the adhesive-bonding of screwing structure is not brittle at cryogenic temperature. This is due to inherent property of GFRP.

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The large-sized GFRP dewar has been developed for a 1MJ pulsed superconducting magnet. It is highly desired that the dewar for the use with a pulsed superconducting magnet has to be made of insulating materials to prevent the eddy current heating loss. The glass fiber reinforced plastic (GFRP) is one of the most suitable nonmetallic materials as the structural material of the dewar, because it has characteristic properties such as low thermal conductivity, nonmagnetism, high mechanical strength, and low specific weight. There are varieties of GFRP made of different materials and by different manufacturing method. Selecting the GFRP as the dewar material, care has to be paied to the high strength at low temperature, especially, against thermal shock, and the permeability of helium gas of the GFRP.
There have been only few papers on the development of the large-sized GFRP dewar. Those dewar were made by the filament winding method and/or the hand-lay-up method in one united body. On the contrary, the GFRP dewars in the present study have been made by the adhesive-bonding method, because this method is accommodating to the dewar design of complex structure.
The designing philosophy together with the selecting of GFRP materials have been presented and discussed. Requirments to design the large-sized dewar are (1) the dewar has to bo made strong enough by selecting proper materials and suitable structures which minimize the concentration of the stress and (2) the dewar has to be vacuum-tight by using the materials of low permeability of helium gas. As the materials, the GFRP's made by the vacuum impregnation method and the filament winding method have been used. To avoid the large ripping force at adhesive-bonding part, the dished bottom plate has been used. Because of the mechanical anisotropy of the bottom plate, the stress is apt to be concentrated on the weakest point of the adhesive-bonding part. Therefore, the GFRP with the glass cloths laminated in the uniform directions has been suited to make the bottom plate.
The calculation of thickness and the estimation of heat insulating performance have been made. The manufacturing, the inspections, and the performance tests have been actually done. The heat loss has been estimated to be 0.7-3.8W, which agreed with the measured value 0.6-0.8W for the developed dewar. This heat insulating performance is fairly good.
The present development of the large-sized GFRP dewar is showing a success of the present bonding methodology.

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A theoretical discussions was presented on the coupling-current loss in a superconducting sub-cable composed of three or seven multifilamentary wires. Approximate expressions for the induced loss by the application of a changing transverse magnetic-field were given as functions of the sub-cable parameters such as the thickness of the outer sheath inside the wire and the degree of the compaction or the solder-filling of the sub-cable. According to the present results, increase of the loss per unit volume of a sub-cable due to the first-stage cabling is not so large as predicted by Campbell's theory which is applicable only to a special type of sub-cable composed of many strands.

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