Development of a Long-Life Stirling Pulse Tube Cryocooler for a Superconducting Filter Subsystem
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We have developed pulse tube cryocoolers for high temperature superconducting (HTS) filter subsystems used in the base stations of mobile telecommunication systems. In July 1999, we reported on our development of a 5 W Stirling pulse tube cryocooler with a contact-type compressor,1 with a cooling capacity of 5.5 W at 80 K for 200 W of input power. However, demands for a smaller-sized cryocooler with higher efficiency and with 5-year reliability prompted us to develop such a cryocooler with a U-type expander and a flexure-bearing-supported linear compressor with opposed pistons.
We have developed an HTS filter and a long-life Stirling pulse tube cryocooler to cool the filter whose cooling capacity is around 1W at 80 K, as previously discussed in a progress report.2 For a compressor input power of 60 W at an operating frequency of 52 Hz and a pressure-volume (P-V) work of 26 W, and for a compressor efficiency of 45%, this cryocooler achieved a cooling capacity of 1.05 W at 80 K (0.63 W at 70 K), a specific power of 92 W/W, 5.5% Carnot (3.9% Carnot at 70 K), and a specific P-V work of 40 W/W, with a minimum temperature of 57 K in an ambient of 23°C.
The key devices of this filter subsystem are an HTS filter and a low noise amplifier (LNA). The HTS filter is made from a YBCO HTS thin film and has a fractional bandwidth below 1.2% at 2 GHz and has a minimum insertion loss at 0.3dB. The HTS filter and the LNA are operated at a constant temperature of 70 K and the cooling capacity needed by them is 0.6 W. We integrated them with the cryocooler into a subsystem, and the external dimensions of this system are 194 mm high, 180 mm wide, 250 mm deep, with a total volume of 8.7 L.
KeywordsHigh Temperature Superconducting Cooling Capacity Pulse Tube Laser Vibrometer Fractional Bandwidth
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