Magnetic analysis and cross-talk fields for the ESS MEBT quadrupole magnet

The focusing lattice of the Medium Energy Beam Transport (MEBT) section of the European Spallation Source (ESS) linac is formed of 11 identical quadrupole magnets, the design of which was determined by beam requirements, spatial limitations and nearby instrumentation. Each magnet is only 89 mm long, produces quadrupole fields above 2.74T, and includes embedded steerer coil systems that excite dipole fields of up to 20G m. In this work, a comprehensive magnetic analysis of the ESS MEBT magnet will be presented through a combination of simulations and measurements. A magnetic model was updated and benchmarked with measurements. An integrated steerer system with coils wound on its return-arms was used to simplify mechanical design and improve magnetic field characteristics in comparison to others with coils integrated into their poletips. Steering field strength and harmonic content were studied versus quadrupole field excitation. Cross-talk fields were investigated for an MEBT doublet magnet system with magnetically shielded diagnostics positioned between its magnets. Due to this magnetic shielding, integrated quadrupole field was decreased by 3% and steering fields by 20% with respect to values calculated using a single magnet model.