A dilution refrigerator of 80-730μmol/s3He circulation rate has been built and the lowest temperature of 2.85mK is continuously attained. In this refrigerator, the discrete heat exchangers with pressed metal (Cu and Ag) powder are used. These discrete heat exchangers are newly developed based on the analysis of Radebaugh and Siegwarth. The machine is designed for many uses such as a base of nuclear cooling and studies of general solid state physics. The design and construction of the heat exchangers and the mixing chamber are described in part I. And the design and construction of the other parts and the performance of the refrigerator will be described in part II.
The details of the design and construction of the heat exchangers and the mixing chamber for the dilution refrigerator have been described in the part I of our papers. In this paper (part II), the technical points in the design and construction of the still, 1K pot, flow impedances, dewar vessel and safety system for long period of operation and also the performance of this machine are described.
Materials for the F. R. P. cryostat should be selected out of various Fiber Reinforced Plastics. A F. R. P. cryostat for pulsed superconducting magnets has been made of F. R. P. by filament winding method. Its inner diameter is 200mm and the depth is 800mm. The evaporating rate of liquid helium was 0.42l/H initially and was 0.45l/H after one month.