Heat load budgeting of a superconducting induction heater‘s commercial cryocooler-based cryostat

Within a project funded by the German Federal Ministry for Economic Affairs and Energy (BMWI), the Karlsruhe Institute of Technology (KIT) collaborates with the Theva GmbH and Bultmann GmbH to develop a superconduct-ing magnetic heater. The Theva GmbH designs and supplies the high-temperature superconducting (HTS) coil. It will be integrated in a cryostat designed and supplied by KIT and cooled to ca. 25 K via a GM-cryocooler. Granted successful test results at KIT, the cryostat with the superconducting coil will serve to operate an induction heater at the Bultmann GmbH and be assessed there under industrial conditions. The challenge within the cryogenic design lies in the simultaneous requirement of relatively low production costs, robustness and extremely limited operation downtimes to form a competitive product. This contribution presents aspects of the cryogenic system’s conceptional design, with a focus on its heat load budgeting. Due to the limited cooling capacities of cryocoolers on each stage, the main aim of the design is to distribute the estimated heat loads as suitably as possible between the cryocooler stages. In the cryostat we designed, the total heat loads on both cryocooler stages will have three significant contributions: heat conduc-tion along connected components, Joule heating and thermal radiation. The respective estimation methods for these heat loads and their results are briefly shown and evaluated in this contribution. In this context, specific examples for the results‘ influence on the cryostat design within the scope of thermal and economical design are given. The heat load approximations’ eligibility to serve as a determination basis of an appropriate cryocooler model is discussed as well. On this basis, finally, we give suggestions for specific cryocooler models currently on the market.