Operation and analysis of planar cryotrons and simple cryotron circuits

Simple cryogenic loops containing two drive cryotrons and a number of sensing cryotrons have been constructed. It is possible with such loops to study both the operating characteristics of the individual cryotrons as well as the static and dynamic switching characteristics of the loop. Some of the characteristics of the individual cryotrons and the reproducibility of cryotrons with these characteristics are discussed. The speed with which current can be transferred from one branch of the loop to another has been both measured experimentally and calculated theoretically from the dimensions and various measured parameters of the loop and its cryotrons. There is found to be good agreement between theory and experiment. The loops have been run dynamically in an effort to detect thermal effects associated with heat dissipation in the resistive cryotron elements. The upper limit to the dynamic operation is currently set by the viewing equipment and, to date, no adverse heating effects have been observed.