11T dipole short model coil metrology at cold and measurement of its thermal contraction

The main objective of the HL-LHC project at CERN is to increase the LHC peak luminosity by a factor of five and the integrated luminosity by a factor of ten. The increased integrated and peak luminosity requires to improve the cleaning efficiency of the collimation system with the installation of new collimators in the cold section of the machine. In order to create the space for such equipment a set of two new high field magnet (here referred as 11T dipole) will replace one standard LHC dipole leaving free space in middle for the new equipment. The metrology tests of one of the 11T dipole short model coils (1.97 m long) have been performed at CERN, using close range photogrammetric techniques, in order to evaluate the mechanical behaviour of the coil. For this measurement, the coil has been immersed and completely covered by nitrogen gas for the thermal cycling (ΔT ≈ 178 Κ). In this paper, some of the environmental constraints are highlighted. These constraints have been: a thin vapour cloud on the top of the cryostat, a small ice layer that has been formed a few minutes after the opening of the cryostat cap and the high temperature gradient for measurement rays. As result, it can be concluded that the short model coil of the 11T dipole is a flexible structure that contracts and bends (bending of 4.85 mm between warm and cold state of the coil). In addition, the best estimate for the coefficient of thermal expansion of the coil is 12.8 μm/m/K what is probably not enough to characterize the short model coil as a composite structure.