液氦温区脉管制冷机的优化实验

研制了一台用作德国国家标准局 (PTB)约瑟夫森效应 (JosephsonEf fect) 1V电压标准冷却系统的二级脉管制冷机。其设计要求在 4 2K提供 1 0 0mW左右制冷量 ,并同时冷却 70K左右的冷屏。采用额定功率为 1 8kW的氦压缩机驱动脉管制冷机 ,在不同制冷量负荷条件下分别对其进行了优化。初步实验结果表明 ,在输入功率 1 8kW的情况下 ,该制冷机最低制冷温度达 2 8K ,4 2K制冷量最大达 1 90mW ,制冷系数达 1 0 6× 1 0 4,火用效率最高达 1 1 3% ,可以充分满足冷却电压标准芯片的需要。此外 ,还与用 6kW压缩机驱动同一制冷机的实验结果进行了比较。

FURTHER EXPERIMENTS OF A 4K TWO-STAGE PULSE TUBE COOLER FOR OPERATION OF A JOSEPHSON VOLTAGE STANDARD

Cryogen free operation of Josephson voltage standard requires a low noise cryocooler that provides a cooling power of 100 mW or less at 4 2 K Due to its intrinsic low level of mechanical vibrations a pulse tube cooler(PTC)appears to be a suitable candidate for such an application Here we report on the performance of a two stage 4 K PTC for operation of a Josephson voltage standard The cooler is driven by a GM type helium compressor with a nominal input power of 1 8 kW(Leybold RW2)in combination with a rotary valve that is spatially separated from the cold head At a peak to peak pressure variation of 0 63 MPa and a frequency of 1 Hz,minimum no load temperatures of 2 8 K and 56 K have been achieved at the second and first stage,respectively The cooling power of the second stage is larger than 190 mW at 4 2 K at an electrical input power of 1 8 kW The results are also compared with those driven the same cooler by a 6 kW compressor