Variation of the residual resistivity ratio of the aluminium stabiliser for the compact muon solenoid (CMS) conductor under dynamic stress at 4.2 K

Superconducting detector magnets are frequently manufactured with aluminium stabilised NbTi cables. Actually there are two new detectors in fabricatio n, namely the CMS and the ATLAS detector at CERN in Geneva, Switzerland. Fo r the CMS project we have studied the variation of the residual resistivity ratio (RRR) of high purity aluminium (HPA) (99.998 %) under dynamic mechan ical stress, applied at 4.2 K, and in a transverse magnetic field of up to 6 T, This information is required for the design of the quench protection s ystem. Because of the mechanical weakness of HPA, a high strength aluminium (HSA) alloy reinforces the CMS-conductor; According to the specification f or CMS, the conductor at maximum field is strained up to 0.15 %, At this st rain the HSA is still in the elastic regime, whereas the HPA is already def ormed plastically. Applying a full stress cycle (e.g. loading and unloading of the magnet), the HPA is deformed first under tension and then under com pression, resulting in a decrease of the RRR, For many stress cycles the de crease is continuous, but saturates after about 500 cycles, The obtained re sults confirm that the RRR for HPA at zero field and after 1000 stress cycl es remains >950, which is largely within specification.