MD #453 Effect of low frequency noise Goal: Can low frequency noise cause emittance growth and stronger population of tails? Motivation: measurements show that the IT amplifies low frequency vibrations (ground motion) by up to a factor 100. These frequencies are possibly already visible in the LHC! HL-LHC aims at β*=15 cm => βmax,IT = 20 km (compared to 6 km at β*=40 cm LHC) possible effects: luminosity loss (emittance growth) higher losses at collimators (tail population + orbit deviation at collimators) Is a more careful design of the IT cryostats necessary? Do we need an additional local high frequency orbit feedback (0.1 Hz – 100 Hz) Q1, vertical M. Guinchard et al. Courtesy first vertical IT eigen-frequency beam 1, vertical preliminary!

MD #453 Effect of low frequency noise possibility to merge MD #284 (Beam tail population measurements using collimator scans), however 1 train colliding with 1 bunch is highly favored over 1 bunch colliding with 1 bunch flat top, squeezed beam 1: 1 nominal 25 ns train emittance measurements with BSRT and wire scanners Scenario 1 (preferred): diamond detectors are available and working reliably: procedure: collimator scans on beam 2 to determine tail population (losses of individual bunches can be reconstructed thanks to high sampling rate of diamond detectors) Scenario 2: diamond detectors are not available: beam 2: bunch 1 procedure: collimator scan on beam 2 -> distribution without excitation a) apply low frequency excitation/repopulation of halo (30 min) b) collimator scan on beam 2 -> distribution with excitation a) repopulation of halo b) collimator scan on beam 2 -> distribution without excitation as reference beam 2: bunch 1 = reference bunch, bunch 2 = colliding with 1 train, bunch 3 = colliding with 1 train + low frequency excitation bunch train excitation single bunch 1 2 3 Beam 1 Beam 2