This contribution presents the design and construction of a setup to measure transport AC losses in high-temperature superconducting coils based on a calorimetric approach. The evaporation of the cryogen (nitrogen) related to the dissipation of energy is collected by using a 3D printed bubble collector that guides the gas into a flow sensor. A box-inside-a-box approach is used to surround the measurement chamber with a cryogenic environment. This approach allows re-directing the heat transfer from the surroundings into an intermediate zone (space between external and internal box). Since this intermediate zone operates under cryogenic temperatures, the noise and the heat transfer in the internal part of the setup are reduced. The main signals (AC current, DC voltage of the power supply used for calibration and measured flow) are concentrated in a small circuit board and recorded by using an Arduino Uno and a Matlab App. This app shows the current values of the variables and a plot of the stored data.
Each measurement is done by considering a 60 minutes load cycle. During the first 30 minutes, the evaporation of cryogen related to the dissipated energy in the coil is measured. The background flow is measured in the next 30 minutes, when nitrogen re-fills can be done. Therefore, one can study the background flow behaviour during the whole measurement time and detect possible changes in the conditions of the environment that can influence the accuracy. The results are presented as average values and standard deviation, which allows studying the amount of variation and dispersion of the data and assess the uncertainty in the measurements.
A well-known resistance is used to build a calibration curve that allows translating the flow of evaporated nitrogen into dissipation in Watts. In this contribution, we present the results of AC transport losses in a racetrack coil made with a 2 mm wide REBCO tape.

Acknowledgments:
The underlying work of this article was funded by the German Federal Ministry for Economic Affairs and Energy (project name ‘‘SupraGenSys’’, funding reference number 03EE3010D). The responsibility for the content of this article lies with the authors and does not necessarily reflect the opinion of the SupraGenSys project consortium.

Keywords: AC losses, Calorimetric measurements, Coil, High temperature superconductor