Shinku

By means of the low background mass spectrometer, as previously reported, we could study several problems encountered in ultra high vacuum techniques. Structural elements of metal high vacuum system, behaviour of the getter ion pump, and components of residual gases were investigated. This paper describes some experimental results since the previous reports.

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Recent developments of the cryogenic processes bring us to find the most efficient method of heat insulation. The most promising method is seemed as the “Vacuum-Powder Insulation.” The heat conductivity of the powder is reduced as the pressure is decreased, and reaches to the minimum value at the pressure which seem still higher than the pressure for “high vacuum method”.
In this case, it is terribly hard to evacuate the powder, because it contains gases and vapors, and has a relatively high resistance when gases flow through powder.
It is very important to find this resistance or conductance to estimate the evacuation time of the actual cryogenic insulation, or to find pressure distribution in the insulating material, and so on.
We measured the conductance of a cylindrical space filled with -30+40 mesh “PERLITE” (diameter is about 0.5mm.) as the powdery material, using the apparatus shown in Fig. 2. The detail configuration of the cylinder is illustrated in Fig. 5, and the measured values of conductance of inner diameters of 80mm, and 40 mm are plotted in Fig. 10.
These values were calculated by equation (7), and reduced the values for filters which are shown in Fig. 7.
Finally, the conductance of PERLITE is shown in Fig. 13 accompanied with the values of capillary tubes of diameters of 4 mm, 3 mm and 2mm.
In the figure, we can find that in the PERLITE, the air flow seems as “viscous” at the pressure above 10mmHg, as “slip” between 10-0.1 mmHg, and as “molecular” below 0.1 mmHg.
This coincides fairly with the change of heat conductivity by the change of pressure, and the calculated values of mean free path of the air when the free diameter of the space is esteemed as about 0.5mm.

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