Development, Integration, and Test of the MACQU Demo Coil Toward MADMAX Quench Analysis

Abstract

The MADMAX project aims at detecting axion dark matter in the mass range of 100 μeV. To facilitate axion to photon conversion with detectable rate a superconducting dipole magnet with a large bore is needed. The MADMAX dipole magnet has to generate ∼9 T in a 1.35 m aperture over ∼1.3 m in length. A key challenge for a magnet made of a cable in-conduit conductor (CICC), operating at 1.8 K with an indirect bath cooling is the quench detection. In order to validate feasibility, a mock-up coil with a quench behavior scalable to MADMAX was designed and produced. The paper gives an overview of the technical details of the MACQU test coil. The conductor, the magnet, the busbar and the supporting and cryogenic systems were designed at CEA. The cable was manufactured in China at the Chang Tong INC from WST Nb-Ti strands, the insertion and compaction was achieved in the ASIPP institute with a copper profile from Aurubis. The winding of the coil and the busbar pre-forming were performed at Bilfinger Noell as well as the assembly of the supporting structure and the thermal shield. The magnet was integrated in the JT60 test station at CEA Saclay and extensively tested. The magnet current reached 80% on the loadline instead of 90% as expected at nominal. The limitation is likely coming from uneven current distribution at the extremity of the magnet at the connection box location. Nevertheless, quench tests were successfully performed at constant currents from 10 kA to 17 kA. They proved that the initial quench velocities are of the order of 1 m/s to 10 m/s, high enough to safely detect a voltage drop in MADMAX and discharge the magnet. In addition, a thermo-hydraulic quench back effect was observed in the MACQU coil cooled by superfluid helium.