Training Performance With Increased Coil Prestress of the 2 m Model Magnet of Beam Separation Dipole for the HL-LHC Upgrade

A large aperture beam separation dipole (D1 magnet) is required to generate a field integral of 35 Tm at 12 kA and 1.9 K for the high luminosity upgrade of the large hadron collider (HL-LHC). High-energy accelerator Research Organization (KEK) fabricated the first 2 m model (MBXFS1) and a magnet test was performed in 2015-2016. Although the quench current reached the nominal operating current, training performance was not satisfactory. The measured azimuthal coil pre-stress was completely released below the nominal current, and this was suggested to be the main reason for the insufficient training performance. After the magnet test, MBXFS1 was disassembled and reassembled as MBXFS1b after increasing the coil pre-stress. In this paper, we report the reassembly of the magnet and test results focusing on the training performance.