PERFORMANCE OF HEAT EXCHANGER MODELS IN UPSIDE-DOWN ORIENTATION FOR THE USE IN HTS CURRENT LEADS FOR W7-X

摘要

The superconducting magnet system of the W7-X stellarator requires 7 pairs of current leads designed for a maximum current of 18.2 kA. Special design feature is the installation of the current leads in upside-down orientation, i.e., the low temperature end is at the top and the room temperature end at the bottom side. This could lead to the problem of free convection inside the heat exchanger (HEX) due to density gradients of the helium between 4.5 and 300 K. The flee convection would lead to a higher amount of He mass flow rate required for cooling. To overcome the problem it was decided to use HTS-material. The current lead can then be cooled with 50 K helium resulting in a drastically reduced density gradient between 50 K and 300 K.