Toyoichiro Shigi

Anomaly of One-Stage Double-inlet Pulse Tube Refrigerator

Publisher Summary Among many modifications of the pulse tube refrigerator, the double-inlet type devised has great advantages in its improved performance and its simplicity. This chapter investigates the performance of one-stage double-inlet pulse tube refrigerator in detail. One-stage double-inlet pulse tube refrigerator generates a low temperature 23.9 K. Anomalous temperature variation occurred in the pulse tube against the bypass valve opening, which is considered to be common in this type of the pulse tube refrigerator. In order to make clear the reason for this anomaly, experiments are performed and reasonable conclusion is obtained. With opening the bypass valve, the temperature distribution along the pulse tube changes from the one with low temperature (∼220 K ) at the position T4 of the pulse tube to the other with high temperature ( ∼270 K ) at the position T4.

Investigation of annealing effects of ultra pure copper

Abstract In relation to construction of the copper nuclear demagnetization stage, the residual resistance ratios (RRR) of ultra pure (7N) copper plates after annealing at various conditions were measured. Ultra pure copper is so active that even a small amount of oxygen diffused into the copper decreases the RRR value considerably. However, if oxidized layers were formed on the copper surface at an early stage of the annealing, the RRR value increased up to 10 4 after annealing.

Pool boiling heat transfer characteristics of liquid 3He below 1 K

Abstract Heat transfer characteristics from a flat smooth copper surface to liquid 3 He have been studied between 0.5 and 1 K under saturated vapor pressure. Liquid 3 He behaves as normal liquid down to the lowest temperature among all substances, and has no pre-exciting bubble nucleus and dissolved liquids because of the lowest boiling point and the small surface tension. Therefore, it is expected that liquid 3 He would show unique heat transfer characteristics. The temperature difference between the copper surface and liquid 3 He was measured as a function of heat flux under steady state condition. Kapitza thermal resistance was derived by the study of relation between the heat flux and the temperature difference. In the nonboiling state, the observed data agree with the equation deduced from the convection flow. However, in the nucleate boiling state, the data are not explained with the Kutateladzes correlation. In the film boiling state, the data are in accordance with the Breen and Westwaters correlation. The observed nucleate boiling state was subdivided into three regions by its characteristic behavior. A boiling model is proposed in order to explain the observed behavior qualitatively.

Vortices in Bi2212 single crystal under magnetic fields tilted to c-axis

Abstract The vortex structure of a Bi 2 Sr 2 CaCu 2 O 8 (Bi2212) single crystal was investigated using a vibrating reed technique. Below about 30 K, the reed touched to a electrode above the magnetic field B s , which was caused by the large magnetic torques originating from the intrinsic pinning and/or the flux pinning perpendicular to the CuO 2 plane. The value of B s depends on the angle between the applied magnetic field and the CuO 2 plane. The temperature dependences of B s were measured at the various conditions.

Surface Treatment of Aluminum Heat Switch

Publisher Summary Aluminum has the high Debye temperature and has no isotope, the former corresponds to the low lattice thermal conductivity at low temperatures and the latter to the high electronic thermal conductivity also at low temperatures. Therefore, aluminum is the most promising as a material of the heat switch over the other materials. Although aluminum is the most promising as a material of the superconducting heat switch at ultra low temperatures, it has not been widely employed so far. The reason is that it is very difficult to ensure the metallic contact between the aluminum strip and the copper holder. In order to realize such a condition, sputtering and plating of gold on the aluminum surface are tried after mechanical polishing, chemical etching and chemical substitution. Evaluation is done by measuring the electrical contact resistance between the aluminum specimen and the copper holder at 4.2 K. The gold-plated specimen and the gold-sputtered specimen, both treated in the Bonder-dip solution beforehand, showed the same contact resistivity, 5 n Ω/cm 2 , the lowest value ever reported.

Experimental Study of the Dilution Refrigerator without 1K Pot

Publisher Summary This chapter helps in constructing a simple dilution refrigerator without 1K pot, and it investigates its basic characteristics extensively. Several features peculiar to this type of the dilution machine have become clear for the first time and they are discussed in detail. The 3He-4He dilution refrigerator without 1K pot liquefies the circulating 3He by Joule-Thomson expansion and by making use of refrigeration capacity of the still and the 3He gas evaporated from it. The highest 3He inlet pressure is less than 1.4 atm, which enables one to circulate 3He without a compressor. The lowest temperature of the mixing chamber is 19.8 mK and highest temperature is 570 mK. The 3He circulation rate is limited in the range of 40 ∼ 70 μ mol/sec. Over this rate, the mixing chamber temperature becomes unstable.

Heat transport in pool boiling liquid 3He below 1 K

Abstract The heat transport characteristics of liquid 3He and 3He 4He liquid mixtures (37% 3He, 15% 3He) were measured under saturated vapour pressure between 0.5 K and 0.7 K. The temperature difference ΔT between the heated copper surface and the liquid just above the surface was measured as a function of the heat flux q ˙ . The transition from the convection and conduction region to the nucleate boiling region was observed clearly for each sample. The curves of q ˙ versus ΔT for increasing and decreasing heat flux reveal no hysteresis effect at 0.5 K, but one at 0.7 K.

Effect of surface roughness on the eddy viscosity of superfluid4He

Abstract The viscosity of liquid 4 He has been measured by means of a torsional oscillator. Below the superfluid transition temperature T λ , the eddy viscosity in addition to the viscosity caused by the normal component was observed when the mean velocity of the cell wall exceeded the critical velocity. In the case of a cell with rough wall, the critical velocity was low and the magnitude of eddy viscosity was large compared with a cell with smooth wall. This indicates that the effect of surface roughness is to enhance the growth of the quantized-vortex tangle.

Pressure Gradient Caused by Quantized Vortex in Superfluid Helium

Publisher Summary This chapter illustrates that a great deal of experimental and theoretical studies on superfluid turbulence have been performed. However, the chapter investigates the influence of the vortex line on pressure dissipation This chapter measures the temperature difference and the pressure difference through He II in a capillary glass tube. It calculates the quantized vortex line density from the temperature difference data using the numerical scaling coefficients. The pressure difference data give the information of interaction between the vortex line and the tube wall. The pressure dissipation caused by the vortex line is only one tenth of mutual friction between the vortex line and the normalfluid. In the terms of eddy viscosity for superfluid velocity field, it calculates the coefficient of the interaction between the vortex line and the superfluid.

Nuclear specific heat of copper potassium tutton salt

The specific heat of copper potassium tutton salt has been measured down to 1 mK in order to investigate the hyperfine interaction of this copper compound. The magnetic ordering of the electronic system occurs at 29.5 mK in zero field. Below the transition temperature the electronic heat capacity decreases and the copper nuclear heat capacity of hyperfine splitting becomes dominant in the heat capacity of the compound. The nuclear heat capacity has a broad peak around 3.5 mK. The entropy of copper nuclear spin, which was calculated from the specific heat data, remains at 40% of ln(2I+1) at 1 mK.