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Description
For high-field accelerator magnets of the future, Bi-2212 round wires are an interesting option thanks to superior Jc compared to Nb3Sn for magnetic fields above 13 T. The round shape of the wires makes it possible to use established Rutherford cabling technology. The large thermal margin results in training-free coil demonstrators. In accelerator magnets, however, Bi-2212 Rutherford cables can be subjected to transverse stresses exceeding 100 MPa due to Lorentz forces. The effect of transverse stress on recent Bi-2212 cables has not been investigated thoroughly yet. In a collaboration between LBNL, NHMFL and the University of Twente, we test the transverse stress tolerance of four Bi-2212 Rutherford cables. The cables are made with 17 strands (Ø0.8 mm) containing 55x18 filaments with precursor powder made by Engimat. The cables undergo overpressure heat-treatment (OPHT) at 50 bar at the ASC-NHMFL on a reaction holder designed to match the transverse stress measurement rig at UTwente. After heat treatment, the cables are transferred to the measurement holder and vacuum impregnated with CTD-101k epoxy resin. The samples are then tested in the transverse stress rig up to 200 MPa at 4.2 K in a background magnetic field of 11 T. Two samples have been already measured. A 5% critical current reduction was observed at 170-200 MPa for one sample and 120-150 MPa for the second sample. A slight progressive critical current reduction was observed in both samples when cycling between 10 and 200 MPa. The filaments were examined using a SEM after etching the silver matrix. However, no large-scale filament cracking was observed.
| Submitters Country | Netherlands |
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