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.
