End-of-Fill Diffusion and Halo Population Measurements with Physics Beams at 6.5 TeV

Beam halo measurements at 6.5 TeV in the LHC were conducted with a full physics beam via collimator scrapings in end-of-fill MDs carried out in May and July 2016. From the time evolution of the beam losses in a collimator scan, it is possible to extract information on the halo diffusion and population. In the first MD, six scans were performed with two collimators in the vertical and horizontal planes in B1 and B2 respectively. The scans were done with squeezed colliding beams, with and without a gentle continuous transverse blow-up with the ADT (transverse damper) on a non-colliding bunch train. In the second MD, four scans were performed with the same collimators with squeezed colliding beams. The beam losses observed with the standard ionization chamber BLMs are compared to the diamond BLMs, and parametric fits of the diffusion model are applied to temporal loss patterns from colliding and non-colliding bunch trains. The results presented in this note also include the particle escape times and frequency analysis of the beam losses.