Computation of the Strain Limits in Nb3Sn Superconducting Magnets

• Giorgio Vallone - gvallone@lbl.gov (Lawrence Berkeley National Laboratory)

Room: ZOOM Abstract—Numerous experiments have shown that the loads applied to Nb3Sn strands and cables can reduce their critical current. Measurements on uniaxially loaded strands allowed to define clear laws to describe the evolution of the critical surface, in the reversible region, as a function of the applied current, field, temperature, and strain. It is, however, still unclear how these laws can be applied to superconducting magnets. In this seminar, we explore a methodology to estimate the critical current and temperature margin reduction on superconducting magnets due to mechanical loads occurring during assembly, cooldown and powering. The methodology is tested on the MQXF magnet, a quadrupole developed for the High Luminosity LHC, and on a Test Facility Dipole targeting a 16 T field in a 144 mm wide aperture. Results suggest that, because of the stresses arising in the winding, the current limit of the magnets can be lower than the expected short sample limit, and that the most critical region does not always coincide with the peak field location. Finally, we define 3D limits on the coil stress/strain fields, necessary to avoid the onset of irreversible degradation due to filament failure.