Earticle

The pulse tube cooler as an alternative of Stirling, G-M or VM cooler to overcome the requirement from the various application fields is described. The necessity of the object oriented cooler development is explained to realize the cryocooler of more energy-efficient, more reliable, more compact and less expensive than what is currently available commercially.

The properties of the conductor-mechanical, thermal, and electrical-are the key information in the design and optimization of superconducting coils. Particularly, in devices using second generation (2G) high temperature superconductors (HTS), whose base materials (for example, the substrate or stabilizer) and dimensions are adjustable, a design process for conductor optimization is one of the most important factors to enhance the electrical and thermal performance of the superconducting system while reducing the cost of the conductor. Recently, we developed a numerical program that can be used for 2G HTS conductor optimization. Focusing on the five major properties, viz. the electrical resistivity, heat capacity, thermal conductivity, Z-value, and enthalpy, the program includes an electronic database of the major base materials and calculates the equivalent properties of the 2G HTS conductors using the dimensions of the base materials as the input values. In this study, the developed program is introduced and its validity is verified by comparing the experimental and simulated results obtained with several 2G HTS conductors.

The Lorentz force distribution of a high T c superconducting tape with increasing transport currents in magnetic field (Ha) was visualized. The external magnetic field was applied normally to the coated conductor tape surface after zero-field cooling, and the transport current (Ia) was increased stepwise from 0 to 90 % of the values of the critical current (Ic (Ha}) at applied filed, Ha. The field distribution (H(x}) near the sample surface across the tape width (2w) was measured using the scanning Hall probe method. Applying an inversion to the measured field distribution, we obtained the underlying current distribution (J(x}), from which the magnetic induction, B(x) was calculated with Biot-Savart law. Then Lorentz force per unit length was calculated using F(x}=J(x}xB(x}, which appears to be very inhomogeneous along the tape width due to the complicated distributions of J(x} and B(x}.

In this work, the optimized process condition of chemical solution deposition which is used to planarize the surface of the metal tape (which is used to grow IBAD-MgO texture template) was investigated. Y20 3 films were dip-coated on the surface of the unpolished metal tape as the seed and barrier layer. The effects of Y 203 concentration of the solution (0.5wt. %, 1.3wt. %, 2.8wt. %, 5.6wt. %) and the number of coatings on the surface morphology and barrier capability against the diffusion from the metal tape were examined. The surface morphology and the thickness of the film were observed using the scanning electron microscope and the atomic force microscope. The presence of elements in metal tape on the film surface was analyzed using the auger electron spectroscopy. The Y20 3 film thickness increases with increasing the Y20 3 concentration in the solution, and the surface became smoother with increasing the number of coating cycles. The best result was obtained from the Y20 3 film coated 4 cycles using 2.8wt. % solution.

In this study, the electromechanical property of REBCO coated conductor (CC) tape adopting a stainless steel substrate has been investigated. Sample was subjected to uniaxial tension and measured its mechanical properties at RT and 77 K. Ic-Et relations was also studied in which the strain and stress corresponding to the 95'' Ic retention and reversible strain limit were measured. In addition, these results were compared to the case of conventional REBCO CC tape adopting a Hastelloy substrate. As a result, by adopting a stainless steel substrate comparable strength and good electromechanical property to Hastelloy one could be achieved.

The renewable energy source is considered as a good measure to cope with the global warming problem and the fossil energy exhaustion. The construction of electric power plant such as an of T shore wind farm is rapidly increasing and this trend is expected to be continued during this century. The bulky and long distance power transmission media is essential to support and promote the sustainable expansion of renewable energy source. DC power cable is generally considered as the best solution and the demand for DC electric power ha' been rapidly increasing. Especially, the high temperature superconducting (HTS) DC cable system begins to make a mark because of its advantages of huge power transmission capacity, low 'ransmission loss and other environmental friendly aspects. Technical contents of DC HTS cable system are very similar to those of.AC HTS cable system. However the DC HTS cable can be operated near irs critical current if the heat generation is insignificant, while the operating current of AC HTS cable is generally 'elected at about 50- 70% of the critical current because of AC loss. We chose the specifications of the cable core of 'Tres Amigas' project as an example for our study and investigated the heat generation when the DC HTS cable operated near the critical current by some electric and thermal analyses. In this paper, we listed some Technical issues on the design of the DC HTS cable core and described the process' of the cable core design And the results of examination on the current capacity, heat generation, harmonic loss and current distribution properties of the DC HTS cable are introduced.

In superconducting magnet applications, winding methods of the superconducting magnet can be classified into a layer winding and a pancake winding. The superconducting magnet using high temperature superconductor (HTS) with rectangular shape is generally fabricated using the pancake winding method. On the other hand, low temperature superconducting (L TS) magnet may be wound by either a pancake winding or a layer winding. Compared with the layer winding, the pancake winding method has a merit of easy replacement of a damaged pancake module, but it also has a demerit of requirement of splicing between each double pancake modules. In this paper, we investigated characteristics of the layer and pancake winding methods using HTS. Six samples were wound out of BSCCO and Coated Conductors (CCs) by two winding methods and their characteristics were experimentally observed.

In this paper, a noble method for rapid cooldown of pulse tube refrigerator (PTR) was proposed and experimentally investigated. An orifice pulse tube refrigerator generates refrigeration effect by expansion PV work at the cold-end, and its amount is affected by the orifice valve opening. There exists the optimum valve opening for maximum cooling capacity and it varies as cold-end temperature. It is verified from simulation results using isothermal model that the optimum valve opening increases as the cold-end temperature increases. In the experiments, a single stage orifice pulse tube refrigerator is fabricated and tested. The fabricated PTR shows 97.5 K of no-Ioad temperature and 10 W at 110 K of cooling capacity with the fixed orifice valve opening. From experiments, the initial cooldown curve with four cases of valve opening control scenario are obtained. And it is experimentally verified that the initial cooldown time can be reduced through the control of orifice valve opening.

Miniature Joule-Thomson refrigerators have been widely used for rapid cooling of infrared detectors, optoelectronic device, and integrated circuits of micro electronics. The typical J -T refrigerator consists of the recuperative heat exchanger with the double helical tube and fin configuration, J-T nozzle, a mandrel, Dewar and a compressed gas storage bottle. In this study, to predict the thermodynamic behaviors of the refrigerator with a compressed gas storage bottle during the cool-down time, numerical study of transient characteristics for a J-T refrigerator was developed. A simplified transient on dimensional model of the momentum and energy equations was simultaneously solved to consider the thermal interactions of the each component of the refrigerator. To account for effects of the thermal mass of the solid, the heat capacities of the tube, fins, mandrel and Dewar are considered. The results show the charged gas pressure of the gas storage bottle has significant effects on the performance of the J-T refrigerator. At the elevated gas pressure of the gas storage bottle, the large capacity of the compressed gas storage does not need to get the fast cool-down performance of the J-T refrigerator in the cool-down stage.