Magnetization Measurements of High-$J_{\rm c}$$\hbox{Nb}_{3}\hbox{Sn}$ Strands

Abstract

High critical current density Nb 3 Sn wires (J c > 2500 A/mm 2 at 4.2 K and 12 T) are the conductors considered for next generation accelerator magnets. At present, the large magnetization of these strands is a concern within the scientific community because of the impact it might have on the magnet field quality. In order to characterize the magnetic behavior of these wires, an extensive campaign of magnetization measurements was launched at CERN. Powder In Tube (PIT) strands by Bruker-EAS and Restacked Rod Process (RRP ® ) strands by Oxford Superconducting Technology (OST) were measured between 0 T and 10.5 T at different temperatures (ranging from 1.9 K to 14.5 K). The samples, based on strands with different subelements dimensions (35 to 80 μm), were measured with a Vibrating Sample Magnetometer (VSM). The experimental data were analyzed to: 1) calculate the effective filament size and the optimal parameters for the pinning force scaling law; 2) define the field-temperature region where there are flux jumps. It was found that the flux-jump can limit the maximum magnetization of the Nb 3 Sn wires and that the maximum magnetization at higher temperatures can be larger than the one at lower temperatures. In this paper the experimental results and the analysis are reported and discussed. The experimental data were analyzed to: 1) calculate the effective filament size and the optimal parameters for the pinning force scaling law; 2) define the field-temperature region where there are flux jumps. It was found that the flux-jump can limit the maximum magnetization of the Nb 3 Sn wires and that the maximum magnetization at higher temperatures can be larger than the one at lower temperatures. In this paper the experimental results and the analysis are reported and discussed.

Validation of Finite-Element Models of Persistent-Current Effects in Nb₃Sn Accelerator Magnets

“…2). This behavior has been observed in high-J c Nb 3 Sn strands [15]. Above 3 T, with the absence of flux jump, higher J c at 1.9 K leads to an increased magnetization and larger persistent-current effects.…”

Implications of the strain irreversibility cliff on the fabrication of particle-accelerator magnets made of restacked-rod-process Nb3Sn wires

“…Whereas J c values in excess of 3,000 A/mm 2 at 12 T and 4.2 K obtained in RRP Nb 3 Sn wires are sufficient for HL-LHC, magneto-electrical instabilities that stem from magnetic-flux and electric-current fast redistributions in the conductor during current ramping could be challenging 10–18 . These instabilities, referred to as magnetization and self-field instabilities, respectively, generate local heat and temperature rise that can cause magnets to quench at currents significantly below the conductor’s critical surface of J c versus magnetic field B at low and moderate field ranges 10–18 . Reducing the size of Nb 3 Sn sub-elements can mitigate these instabilities significantly, and a sub-element size around 20 μm or less is desirable 1 .…”

Field Quality of HD3—A Nb<inline-formula> <tex-math notation="LaTeX">$_3$</tex-math> </inline-formula>Sn Dipole Magnet Based on Block Design

“…13 and 14). At 1.9 K, flux jumps occur more frequently but with smaller amplitudes [46], which lead to less pronounced fluctuations in field errors [34]. Hence, operation at 1.9 K, cored Rutherford cables to suppress the ISCC and smaller d eff can reduce the random fluctuation of field errors associated with flux jumps.…”