Effect of the Charged Pressure on GM Cryocooler Performance.
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This paper presents experimental results that show that the refrigeration efficiency of GM refrigerators can be improved by applying a charged pressure. Recently, there has been remarkable progress in superconducting systems, such as magnetic resonance imaging systems, silicon singlecrystal pull-up apparatus, and cryopumps. GM cryocoolers are used to cool these systems because of their high reliability. Thus, to improve the efficiency of superconducting systems, it is important to improve the efficiency of GM cryocoolers. If the compression ratio of a GM cryocooler is reduced, its coefficient of performance (COP) will approach the Carnot COP, since the cryocooler will operate with Simon expansion. Therefore, we investigated the effect of varying the charged pressure of a cryocooler and the cycle frequency on its refrigeration efficiency. We developed a GM cryocooler that can be operated at various charged pressures and we measured its efficiency at various charged pressures and operating frequencies. The optimum charged pressure and operating frequency were determined by comparing the experimental results with numerical simulation results.