Design and thermal calculations of FRESCA2 heat exchangers for pressurised superfluid helium baths temperature controlling

In order to characterise and qualify superconducting cables at currents up to 70 kA, at background magnetic fields up to 13 T and at 1.9 K or 4.3 K temperature levels the Facility for Reception of Superconducting Cable (FRESCA2) is currently under design in collaboration between CERN and WUST. The FRESCA2 design using the double cryostat concept, with superconducting magnet external cryostat and a cable sample insert internal cryostat. The magnet and the cable sample are held in the pressurised superfluid helium bath of the particular cryostat, whose temperature is controlled by a heat exchanger (HX), where the saturated superfluid helium (Hells) is used as the cooling medium. The paper presents the design and the thermal model of the HXs as well as the calculation of their minimum area necessary to cool - down the particular bath from 4.3 K to 1.9 K in the required time in respect to an available pumping speed of warm compressors.