TWO-STAGE PULSE COOLER FOR OPEATION OF A JOSEPHSON VOLTAGE STANDARD NEAR 4 K
CP613, Advances in Cryogenic Engineering: Proeedings of the Cryogenic Engineering Conference, Vol. 47,，-0001，（）：
Cryogen-free operation of Josephson voltage standards requires a low-noise cryocooler that provides a cooling power of 100mW or less at 4.2K, and about 1W of precooling at an intermediate temperature near 70K. Due to its intrinsic low level of mechanical vibrations a pulse tube cooler (PTC) appears to be a suitable candidate for such an application. In this work, a two-stage pulse tube cooler has been developed and optimized for cooling of a 1V or 10V Josephson voltage standard near 4K. The performance of the PTC, which is driven by a compressor with a rated input power of 1.7kW, is optimized under three different conditions. So far, a minimum temperature of 2.66K and a maximum cooling power of 202mW at 4.2K with coefficient of performance (COP) of 1.15xlO-4 have been been achieved. The performance of the crycooler is expected to fully satisfy the cooling requirement of the volatge standard. In addition, the experimental results are also compared with those obtained by driving the same cooler by use of a 6kW compressor.
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