Magnetic Properties of Pure Iron for the Upgrade of the LHC Superconducting Dipole and Quadrupole Magnets

The construction of the superconducting magnets for the High-Luminosity upgrade of the Large Hadron Collider accelerator at Conseil Européen pour la Recherche Nucléaire has resulted in demands for 1800 tons of ferromagnetic laminations for the magnet iron yokes. The magnetic properties of the selected steel, ARMCO Pure Iron, have been measured, within annealing treatment sequences from 750 °C to 850 °C, at operation temperatures of 4-300 K. It is shown that annealing treatment improves the magnetic performance of the material if the material is kept at room temperature. However, this improvement disappears after cooling down the material to the operation conditions of 4 K. The dependence on the operation temperature was shown by testing the material at the cryogenic temperature of roughly 4 K, 77 K, and at room temperature. The magnetic performance of the material shown at room temperature has not been found at cryogenic temperatures. Nevertheless, the results obtained are still acceptable in comparison to the properties of the alternative materials. Tests performed before and after the application of a mechanical stress have also been studied to validate the production process.