In general, a cryocooler can be developed using an object-oriented design concept applied to a prototype. There are many various demands, such as, cooling temperature, cooling capacity, reliability and cost, efficiency. On the other hand, a number of cryocoolers has already been developed. Therefore, the basic characteristics of these cryocoolers should be clarified to ascertain their adaptability to current demands. From this perspective, this fundamental cryogenic refrigerator review explains the functions of individual components for specific cryocoolers. Example cryocoolers include a GM-cooler, Stirling cooler, pulse-tube cooler and thermo-acoustic cooler.
The bulk material comprised of (Nd, Eu, Gd)Ba2Cu3Ox(NEG123) shows a high irreversibility field over 14 T at 77.3 K. In order to study the origin of the high irreversibility field, transport measurements of NEG123 and Y123 bulk samples were performed as functions of temperature, high magnetic field and field angle, and transport properties were compared with each other. Dip structures for the angular dependence of resistivity are observed around B//c for all samples. These results indicate that c-axis correlated disorder exists. The NEG123 bulk sample with a larger dip shows a higher irreversibility temperature. In addition, we found that the differences of the irreversibility temperature between on and 12° off the dip are scaled universally as a function of the depth of the dip for NEG123 and Y123 bulk samples. It is considered that c-axis correlated disorder is important for high irreversibility fields.