Collimator losses in the DS of IR7 and quench test at 3.5~TeV

Beam studies to address the limitations of the Phase~I collimation system were performed. The primary goal was to achieve the design loss rates of the collimation system of 500~kW, and to study the behaviour of the system and of the machine in these conditions. The beam-based determination of the quench limits of the cold magnets with highest losses, can also be addresses in this study. Beam tests consisted in increasing the loss rates at 3.5~TeV with nominal machine configuration and collimator settings in order maximise the losses in the dispersion suppressors of IR7, notably in the Q8 quadrupoles that represent the limiting location with highest leakage from IR7. The cleaning performance of IR7 is very good, with a leakage of a few 10$^{-4}$ in the Q8. Therefore, the test had to be performed with stored energies well above the safe limit.