Field Measurement to Evaluate Iron Saturation and Coil End Effects in a Modified Model Magnet of Beam Separation Dipole for the HL-LHC Upgrade

A beam separation dipole magnet for the high luminosity large hadron collider upgrade is developed. The development of the 2-m-long model magnet (MBXFS1) was initiated so as to evaluate the design and performance of the beam separation dipole magnet. In the first cold test in 2016, the quench performance was not satisfactory because the coil prestress at the pole was completely released during excitation. After reassembly to improve the quench performance, the excitation test of the modified model magnet (MBXFS1b) was performed at 1.9 K in 2017 at KEK. Due to the large coil aperture and limited outer diameter of the iron yoke, the control of iron saturation effects on the field quality has been a design issue. Regarding the magnetic performance, field saturation effects on the transfer function and the multipole field variation along the excitation, and coil end effects to the straight section need to be evaluated by the field measurement. In this paper, field measurement results will be presented and the comparison with the three-dimensional field calculation will be discussed.