Low-noise temperature control using a high T_c superconducting sensor compared to a conventional PRT method

摘要

We have made further investigations about the performances of our high stability temperature controller which involves a YBCO strip as the temperature sensor and home-made electronics designed to monitor the critical current of the strip biased at a constant voltage. The new experiments involved three temperature sensors, namely one calibrated platinum resistance thermometer (PRT) and two YBCO strips, all mounted to the same copper block. We have compared the temperature stability around 87 K obtained while using one of the YBCO strips and our electronics to that given by the PRT associated with a commercial high-quality temperature controller. The second YBCO strip was used to measure the out-of-loop temperature fluctuations of the copper block. The RMS values of the temperature variations were about 145 μK when the PRT was used for the temperature control, and about 9 μK with the YBCO strip. Thus, our method improves the temperature stability by a factor of 16 as compared to the PRT control. A two-stage temperature control experiment shows that the expected resolution of a high-T_c ACR based on our scheme is about 70 nW for average power levels in the range of a few nW to 100 μW.