A cryogenic calorimeter based on a superconducting phase transition thermometer with thermal feedback and SQUID read out

Cryogenic calorimeters with superconducting phase transition (SPT) thermometers are extremely sensitive particle detectors. Some characteristics of SPT calorimeters such as linearity and dynamic range often suffer from the superconducting transition shape. The common way to improve the performances is to use the voltage bias to operate the SPT calorimeter in strong electrothermal feedback mode. This method does not allow us to optimize the noise, linearity and dynamic properties simultaneously. We have developed a novel SQUID circuit with thermal feedback which allows to improve the linearity, dynamic range and speed of the SPT calorimeter. Results obtained with a cryogenic calorimeter based on a tungsten thermometer are presented.