We have built and tested a transition edge sensor which monitors temperature change by measuring magnetic flux expulsion from a superconducting element. Flux change is sensed by a dc SQUID coupled to the element using a flux transformer in a gradiometer arrangement. The operating temperature of the sensor can be varied by application of moderate magnetic fields to the superconducting core, using an integrated solenoid. With a Sn core at 3.58 K, the thermometer has demonstrated a noise level of 2.25 nK/rtHz. We estimate that such a sensor will allow femtowatt sensitivity of an absolute cryogenic radiometer presently under development.
Citation: Journal of Applied Physics
Pub Type: Journals
absolute cryogenic radiometer, paramagnetic salt thermometer, radiometry, SQUID readout, transition edge sensor