Design Evolution of MADMAX Conductor to a Nb–Ti Cable in Copper Conduit

Abstract

The MADMAX (MAgnetized Disc and Mirror AXion) project aims at detecting axion dark matter in the mass range around 100 μeV. Prerequisite for success is a very large dipole (1.35 m warm bore) with a high magnetic field up to 10 T. A first conductor design made of Nb-Ti Rutherford Cable On Conduit Conductor with a hole in the copper conduit (RCOCC type) was already presented. The coolant is static bath of superfluid helium at 1.8 K. Unfortunately, no conductor manufacturer with an available production line was found to take in charge the cable insertion/soldering process. Actually, such a production line should be compatible with large conductor section (∼400 mm²) including a solder wave device. The type of conductor was changed to use a line developed for ITER Cable In Conduit Conductor (CICC). Nevertheless, the jacket part was kept in copper. The main evolution of the MADMAX conductor design is presently reviewed. The final outer dimensions of the conductor, the void fraction and the required cold work of the copper induces a reverse engineering challenge on the initial shape of the copper profile. Then, the cable geometry modification involves a lots of differences in terms of self-field, strand diameters, transposition paths, joints technique and conductance between the strands and the stabilizer. The mechanical aspects are subject to evolution for the project due to the magnetic design optimization and conductor type change. A sub-modeling approach is used to detail the stress level in the stabilizer jacket. The possibility of wire motion and wire deformation during the conductor compaction in the production line is also discussed. Concerning the thermal analysis, the major difference is the thermo-hydraulic quench back that induces a much higher pressure drop of the helium in the conduit. So, higher pressure induced higher helium velocity and a fast detection after a quench event in superfluid environment becomes possible.