Evaluation of a 4 K 4-stage pulse tube cryocooler for superconducting electronics.

Market applications of digital and mixed-signal superconducting electronics require the integration of a robust, long life, highly efficient 4 K cryocooler with an equally robust cryopackage including superconducting integrated circuits (ICs). The ideal 4 K cryocooler, with full reliability, power and cost efficiency, and manufacturability, is not yet commercially available. Recently, a custom-designed laboratory prototype of a 4 K 4-stage Stirling-type pulse-tube cryocooler was produced by Lockheed-Martin and delivered to HYPRES. We have adapted the system with a cryopackage which we used to mount and successfully test a superconducting IC with a variety of Nb circuits including an RSFQ binary counter. For 600 W total compressor power and a package with broadband input-output lines, extended stable operation of the counter at T=4.5 K was demonstrated with a clock frequency up to 46 GHz clock speed, with 25 mW of excess cooling capacity on the coldest stage (4.5 K). The thermodynamic and mechanical performance is promising for the development of an improved compact cryocooler for superconducting electronic applications such as wireless communications.