Development and Application of Dilution Refrigerator Constructed with Non-metalic Materials

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The aims of this research are (1) the construction of ^4He-circulating dilution refrigator with non-metallic materials and (2) the realization of spin-polarized liquid ^3He in a stationary state.For the first aim, we succeeded to obtain about 8mK with a plastic mixing chamber and a plastic heat exchanger tube. The construction of a non-metallic de-mixing chamber is found to be very difficult. We should develop a reliable method of sintering of very fine saphire powders.For the second aim, we operated the ^4 He-DR above mentioned in a magnetic field of 6T.We obtained about 12 % polarization at 50mK,which is far from our destination of about 35 %.We will continue the research with much more ^4He-circulating rate.