4 K cryocooler implementation of a DC programmable voltage standard

NIST and HYPRES, Inc. have been collaborating to develop a 1 Volt DC programmable Josephson voltage standard (PJVS) that operates on a closed-cycle refrigerator. The goal of this work is to construct a platform that will allow the chip to work at 4 K without liquid helium, thereby making the system more convenient and eliminating the need for users to handle liquid cryogens. In our existing PJVS systems, the Josephson chip temperature is the only parameter that is not computer controlled. The addition of a cryocooler will allow automated warming and cooling of the Josephson device and enable an intrinsic voltage standard system in which every control function is automated, and the only required user input is the desired output voltage. The cryocooler package is designed to allow PJVS chips to be easily interchanged between the cryocooler and liquid helium cryoprobes.