Speaker
Description
The upgrade of the LHC to increase luminosity (High Luminosity LHC) requires the construction of six different types of accelerator magnets based on LTS technology. Besides the quadrupoles in Nb3Sn, with peak field of 11.5 T, we have two different dipoles in the 4.5-5.6 T range based on Nb-Ti, and three types of correctors. All magnets are characterized by wide apertures (150 mm), posing significant challenges for the large accumulated stress in the midplane.
In this contribution, after recalling the specific features of the project, we will outline a classification of the typologies of the issues found during the design/prototype phase and we will discuss in more detail two cases. The first one is an unexpected contribution to field quality in the separation dipole, due to a cross talk between saturation and 3D effect that propagates well inside the magnet straight part. The origin of the problem, its simulation with finite element methods and the iteration in field quality to cure this effect will be presented.
The second one is a limitation in the magnet performance due to the torque induced by horizontal and vertical field in the coil heads of the nested corrector dipole. The first prototypes showed ability to reach the field requirements, but required retraining when changing the torque sign. A fine tuning of the coil design allowed to considerably reduce this issue, proving also how sensitive the magnet performance can be on details of the design, even in the case of Nb-Ti magnets.
