Measurements (to be made): About the device (in development): Suppression of persistent-current magnetization of Nb3Sn strands by transport current M2PoA-06 X Xu, M.D. Sumption, M. Majoros, E.W. Collings Center for Superconducting & Magnetic Materials (CSMM), Department of Materials Science & Engineering, The Ohio State University, USA Abstract One of the goals of the Large Hadron Collider Accelerator Research Program (LARP) is to demonstrate the feasibility of Nb3Sn technology for a proposed luminosity upgrade based on large aperture high gradient quadrupole (HQ) magnets. For such magnets field quality at the bore is a critical requirement for which reason it is necessary to fully characterize the persistent-current magnetization of the accelerator magnet, hence that of the cable and the strand from which it is wound. This report focuses on persistent-current magnetization calculated as function of applied transport current. Strand magnetization is generally measured in the absence of transport current. To render the results relevant to magnet-cable magnetization the effect of transport current, I, should be considered. The first to do so was LeBlanc whose analytical calculation showed the magnetization changing according to M/M0=1-(I/Ic)2 where I and Ic (the critical current) are to be evaluated at the particular fields of interest. LeBlanc modelled a semi-infinite slab of superconductor; a practical superconductor is expected to yield a different relationship. In this work we aim to study the transport current effect on magnetization of Nb3Sn. LeBlanc’s model was for a semi-infinite slab, assuming that Ic is constant with B. Practically the following two effects may make the results different. A: the effect of sample shape. We did the calculation for cylindrical geometry, to compare with LeBlanc’s results on slab. Still assuming Ic is constant with B. First B to >Bp, then I to Ic. The comparison of the results is shown in Fig. 5. B: the effect of current/field sequence. For the same cylindrical sample, we studied three cases: 1, I is first ramped up to 0.5Ic, then B is ramped up to 0.5Bp; 2, B is ramped up to 0.5Bp with no current; 3, I and B are ramped up simultaneously up to Ic and Bp, respectively. The current distribution of the three cases as B reaches ~0.4Bp are shown in the Fig. 6. The calculated M(B) curves are shown in Fig. 7. For a Nb3Sn subelement. Calculation parameters: deff=60 μm, Jc(B) follows Kramer’s law. We compared two cases: that B is ramped up without transport current, and that I and B are ramped up simultaneously, with a load line I=0.18B. Assume the load line intersects the short -sample Ic(B) at point (Imax, Bmax), and Bmax=16.5T here. The M(B) curves of the two cases are shown in Fig. 8. Fig. 7 Fig. 8 No visible difference as I/Ic is small (the calculation only went to 0.24 A). Fig. 5 (3) I and B are ramped up simultaneously To find out the field from which the transport current begins to significantly suppress the magnetization. Fig. 9 Conclusion: The difference between the current-on and current-off magnetizations is not significant until close to the operational field of a magnet. The Ic(B) of Nb3Sn follows Kramer’s law: Assume Bmax values of 12 T and 16.5 T (for two different magnet strand lines) and a Birr of 24 T for the Nb3Sn strand with which it is wound. Plotted in Fig 9: So we obtain: (calculated using LeBlanc’s model; more accurate model for Nb3Sn is being calculated). For Bmax =16.5 T, the difference between M and M0 won’t reach 1% until B reaches 9 T. A device is designed to measure the variation of persistent-current magnetizations of strands with transport current. Measurements (to be made): For Hall sensor I, the magnetizations induced by the transport currents conducted by the two layers of wires are cancelled, so its magnetization is the sum of the applied field and those generated by the wires. By measuring the variation of the difference between the two sensors with the transport current, we can measure the influence of transport current on persistent-current magnetizations of wires. References: 0.5’’ φ1.0’’ φ0.6’’ φ1.26’’ φ0.8’’ R0.4’’ 0.23’’ 0.01’’ 0.0315’’ A groove allowing the wire to pass Hall sensor I Hall sensor II B About the device (in development): A single wire is wound into two layers so that transport current is conducted in the same direction. Between the two layers, a groove is machined across the in-between layer so that the wire can pass. The Hall effect sensor I is put between the two layers of wires, while sensor II is outside the wires so that it only measures the applied field B. 1. M. A. R. LeBlanc, Phys. Rev. Lett., Vol. 11, Issue 4, Pages 149-152, Aug 1963 2. X. Xu, M. Majoros, M. D. Sumption, and E. W. Collings, IEEE TRANS. APPL. SUPERCON., VOL. 25, NO. 3, JUNE 2015, Pages 8200704 The device material: Ti-6Al-4V. Acknowledgements Funding was provided by the U.S. Dept. of Energy, HEP, university grant DE-SC0011721