A HIGH-STABILITY TEMPERATURE CONTROLLER BASED ON A SUPERCONDUCTING HIGH-T-C SENSOR

An analysis of a temperature control scheme we described in a previous article is given in this paper, showing its intrinsic noise limitatio ns. This scheme made good use of YBCO microbridges as temperature sens ors, We find that high temperature to voltage transfer coefficient val ues (much greater than 1 V/K) are required in order to reach fluctuati on levels well below 100 mu K-pp. Consequently, a new design of the ci rcuit has been made by introducing a current pre-biasing technique of the microbridge and allowing very large offset compensations, A transf er coefficient value of 441 V/K was used to obtain a temperature contr ol with fluctuations less than 1.6 mu K-pp over a 2 hour recording tim e, Such high stability temperature controllers leading to fluctuation levels in the mu K-p range can prove to be very useful for high-T-c SQ UID systems working at 77 K and in high-T-c bolometer applications.