Simple differential thermometer for low temperatures using a thermocouple with a SQUID detector

Abstract
Details of design and construction of a simple and rugged thermocouple differential thermometer are presented. Gold +0.03 at. % iron wire is used, with niobium leads connected to a SQUID. It is demonstrated that at 1 K the response time is about 15 ms and that the temperature sensitivity of 10−7 K with a 10-Hz filter is Johnson-noise limited. Additional qualities such as small size, little self-heating, and high reproducibility make this device ideal for differential thermometry at low temperatures.