Fabrication of a Second-Generation of $\hbox{Nb}_{3} \hbox{Sn}$ Coils for the LARP HQ02 Quadrupole Magnet

In the framework of the Large Hadron Collider Luminosity upgrade (HiLumi-LHC) project, the US LHC accelerator research program is developing high-gradient, large-aperture Nb3 Sn quadrupole magnets for the LHC interaction regions. The fabrication and tests of a first series of 120-mm-aperture “HQ01” coils revealed design issues that resulted in limited performance. A second series of coils was fabricated in which a number of improved features were implemented (HQ02 coils). The improvements were partly validated with the successful test of an HQ02 coil in a mirror structure, which reached 97% of the short sample. Here, we review the modifications in the coil design and the coil fabrication process, report the issues met during the fabrication, give details of the few differences that exist within the set of HQ02 coils, and discuss a list of further improvements that will be implemented in a third series of HQ coils.