Preliminary Assessment of an Ultrasonic Level Sensor for the Calorimetric Measurement of AC Losses in Superconducting Devices

Superconducting materials show no resistivity under DC regimes and can generate extremely high magnetic flux densities, allowing for the development of disruptive or improved power grid applications. Yet, under AC, they experience losses that must be removed by the respective cryogenic system, which is responsible for maintaining the superconducting state. Measuring these losses is of utmost importance, e.g., for monitoring the condition of superconducting devices. In this paper, a new calorimetric method for measuring AC losses in superconducting systems is investigated. The proposed concept infers the level of the cryogenic fluid in a cryostat by measuring the echo time from sound waves reflected on it. The thermal energy (losses) that leads to fluid evaporation is then calculated. Using this method may lead to a faster and more direct approach to measuring losses when compared to other concepts, even if the sensor shows some error factors, as well as strict environmental requirements for its operation. A prototype of the sensor is tested in liquid nitrogen, and a preliminary assessment of its performance is carried out.