Part II of this study covers the variations of loss mechanisms for not only cryocoolers, but also compressors. To do so, it is inevitable to understand the efficiency of a system in terms of percent Carnot and/or a coefficient of performance. Once readers review these concepts, the next step is how to minimize the losses and optimize the entire refrigeration cycle. As described in part I of this study, a GM cryocooler is employed to study the loss mechanisms in detail. By introducing the concepts of energy flow, work flow, enthalpy flow and entropy flow, it is fairly straight-forward to visualize the refrigeration process. This approach is effective to optimize the refrigeration cycle, and a numerical method is used to demonstrate optimization of the GM cooler. To review the historical background of GM coolers, the Solvay cycle is also described to compare efficiencies.
We have reported high-Jc Sm1+xBa2-xCu3Oy (SmBCO) films prepared by a low-temperature growth (LTG) technique. The LTG-SmBCO films showed a Jc of 0.28 MA/cm2 (77 K, B//c, B=5 T). However, the Jc of these films in the magnetic fields above 5 T dropped and were lower than that of NbTi wire (4.2 K). In this study, we introduced nanoparticles with low Tc (low-Tc-nanoparticles) into LTG-SmBCO films to improve the Jc at the high magnetic field. The LTG-SmBCO + 1.4 vol.% nanoparticle film result in a Jc of 0.37 MA/cm2 (77 K, B//c, B = 5 T) and 0.10 MA/cm2 (77 K, B//c, B = 8 T). Furthermore, the Jc at 65 K in a field of 16 T (B//c) reached 0.05 MA/cm2. Elemental mapping clarified that LTG-SmBCO + 1.4 vol.% nanoparticle film had nanosized low-Tc particles with an x of 0.15-0.30 and low-Tc network with an x of 0.05-0.15, which were dispersed in the high-Tc matrix. We speculate that the Jc under high magnetic field conditions depends not only on the distribution and size of low-Tc regions, but also on the Sm/Ba composition within the low-Tc regions.