Cryogenic Design of a Superconducting Magnet With a Copper Cable-in-Conduit Conductor Filled With Static Superfluid Helium

In the field of dark matter research, the MAgnetized Disk and Mirror Axion eXperiment (MADMAX) aims for the direct search of axions in a mass range around 100 $\mu$ eV. To have enough sensitivity on this range a dipole composed of 18 coils must reach a figure of merit of 100 T $\mathbf {^{2}}$ m $\mathbf {^{2}}$ . For this purpose, the use of a cable-in-conduit conductor (CICC) with a copper profile filled with static superfluid helium is under investigation. In order to prove the reliability of such a conductor in this magnet design as well as characterizing the quench propagation, a magnet solenoid mockup is tested within the JT60SA cold test facility (CTF). To reproduce the thermal configuration of a MADMAX coil, the solenoid mockup is cooled down at 1.8 K directly through the void section of the CICC by pressurized superfluid helium and the mandrel, by conduction, without being immersed in a helium bath. The long distance to the heat exchanger coupled with the narrow helium section in the CICC limits the Gorter–Mellink heat transport, thus the cool down efficiency and heat losses must be tackled. This article describes the thermal design of the experimental facility, the explanation of a thermal model for superfluid helium cool down and operation, and the first experimental results.