Abstract
The development of high-field accelerator magnets capable of providing 16 T dipolar fields is an indispensable technological breakthrough needed for the 100 TeV energy-frontier targeted by the Future Circular Collider (FCC). As these magnets will be based on Nb$_3$Sn Rutherford cables, the degradation of the conductor performance due to the large electro-magnetic stresses becomes a parameter with a profound impact on the magnet design. In this work, we investigated the stress dependence and the irreversible reduction of the critical current under compressive transverse load in high performance Powder-In-Tube (PIT) Nb$_3$Sn wires. Tests were performed in magnetic fields ranging between 16 T and 19 T on wires that were resin-impregnated similarly to the wires in the Rutherford cables of accelerator magnets. The scope was to predict the degradation of the cable under stress from a single-wire experiment. Interestingly, the irreversible stress limit, $\sigma_{irr}$, defined as the stress level corresponding to a permanent reduction of the critical current by 5$\%$ with respect to its initial value, was found to depend on the applied magnetic field. This observation allowed us to shed light on the mechanism dominating the irreversible reduction of the wire performance and to compare and reconcile our results with the irreversible limits measured on Rutherford cables, typically tested at fields below 12 T.
Highlights
The goal of increasing the potential of discovering new physics is pushing the high-energy physics community to conceive novel experiments based on a highest-energy hadron collider with a center-of-mass collision energy of 100 TeV [1]
The wire impregnated with epoxy type L reaches its irreversible limit at σirr = 110 MPa, which is well below the peak stress of 150–200 MPa of the Future Circular Collider (FCC) 16-T dipole designs. σirr is substantially higher when the wire is embedded in a reinforced impregnation
We have investigated the stress dependence and the irreversible reduction of the critical current under compressive transverse load in high-performance PIT Nb3Sn wires
Summary
The goal of increasing the potential of discovering new physics is pushing the high-energy physics community to conceive novel experiments based on a highest-energy hadron collider with a center-of-mass collision energy of 100 TeV [1]. At the University of Twente cables can be tested under high transverse compression ( 200 MPa) [20] in an external magnetic field up to 11 T, the major limitation being that the load can be applied on a reduced sample length (approximately 5 cm). At Fermilab there is a device that allows measuring Ic under transverse compression of a single superconducting wire housed in a dummy cable up to 200 MPa, 14 T [24] In both cases, stress is applied over a length of few centimeters, 12 cm at NHMFL and 6 cm at Fermilab. We investigated the stress dependence and the irreversible reduction of the critical current under transverse compressive load in highperformance powder-in-tube (PIT) Nb3Sn wires. The measurement campaign focused on two aspects: the influence of the type of impregnation on the irreversible stress limit of the wire and the identification of the main mechanism responsible for the irreversible reduction of Ic
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