Yoshiko Fujii

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.

Heat flow measurements of superfluid 4He in wide tube

Abstract The effective thermal conductivity of superfluid 4 He was measured in the temperature range between 0.48 and 0.67 K using a tube 8 cm in diameter, which is sufficiently wide to neglect the influence of phonon scattering on the wall. The data are compared with the calculations of Landau et al. and Maris and the experimental results of Greywall. The obtained results are useful for analysis of thermal resistance in the ultra-cold neutron production equipment at KEK.

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.

Thermal and magnetic properties of copper potassium tutton salt below 0.15 K

The specific heat and the ac susceptibility of copper potassium tutton salt have been measured between 0.01 and 0.15 K. The magnetic phase transition from the paramagnetic to the canted ferromagnetic state was observed at 29.5 mK in zero field. From the obtained electronic entropy curve this salt is considered to be a Heisenberg-type ferromagnet. The copper nuclear specific heat of the hyperfine splitting is estimated to beCN=1.1×10−5R/ (T2/[K2]), which is one order smaller than the value calculated from previous results of the paramagnetic resonance.

Thermal resistance between liquid3He and copper potassium tutton salt

The thermal resistance between liquid3He and copper potassium tutton salt (CPS) has been measured through its magnetic ordering temperature (Tc=29.6 mK). The thermal resistanceR for pure3He has a broad minimum near 60 mK and increases continuously throughTcwith decreasing temperature, except for a dip atTc. BelowTc,R is proportional toT−1.5. Effects of4He coating have been studied by stepwise addition of4He into liquid3He. The thermal resistance increased drastically for the liquid containing 150 ppm4He and more for 95%4He. By sudden depressurization of the liquid3He containing 480 ppm4He, a considerable decrease ofR was observed. SinceR for pure3He was much smaller than the calculated Kapitza resistance, the present experimental results indicate the existence of surface magnetic coupling between liquid3He and CPS.

Visualization of 3He Nucleate Boiling Below 1 K

Boiling behavior of liquid 3He below 1 K was visualized as shadowgraph image. A light source and a video camera (or still camera) were arranged at room temperature. The light was guided to the 3He cell by an optical fiber, and the shadowgraph image was transferred to the camera by an image fiber. The 3He bubble formed on the heated copper surface was spheroid-like due to the low surface tension. The size at departure from the surface and the relative bubble formation rate were measured as a function of heat flux. The previously obtained heat transfer curve could be explained qualitatively by this boiling behavior.

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.

He II Thermal Counterflow near Superfluid Turbulent Transition

Thermal counterflow of He II in a circular glass capillary has been studied near a transition from laminar flow to turbulent flow. In order to study effects of edge shape of a capillary on the vortex nucleation a sharp edged capillary (tube I) and a tapered capillary (tube II) were used. The temperature difference (ΔT) across the tube was measured precisely using a thermocouple connected to a SQUID detector. The vortex line density Lo was obtained from ΔT data. The critical value of (Lo1/2d)c (d: tube diameter) at the transition for tube II was smaller than that for tube I. The spontaneous periodic fluctuation of ΔT was observed near the transition.

Visualization of 3He nucleate boiling

Abstract The boiling behavior of liquid 3 He was visualized as a shadowgraph image between 0.7 and 1.8 K . A light source and a high-speed camera were set up at room temperature. The light was guided to the 3 He cell by an optical fiber, and the shadowgraph image was transferred to the camera by an image fiber. The 3 He bubble shape on the heated copper surface was hemispherical reflecting the excellent wetting property. The size at departure from the surface and the bubble growth rate were measured as functions of heat flux and temperature.