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MD on nominal collimator settings

MD on nominal collimator settings R.W. Assmann , R. Bruce, F. Burkart , M. Cauchi , D. Deboy , L. Lari , E. Metral , N. Mounet , S. Redaelli , A. Rossi, B. Salvant , G. Valentino, D. Wollmann. Motivation and goal. Presently running with relaxed collimator settings

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MD on nominal collimator settings

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  1. MD on nominal collimator settings • R.W. Assmann, R. Bruce, F. Burkart, M. Cauchi, D. Deboy, L. Lari, E. Metral, N. Mounet, S. Redaelli, A. Rossi, B. Salvant, G. Valentino, D. Wollmann

  2. Motivation and goal • Presently running with relaxed collimator settings • Why go to tighter settings? • Higher predicted cleaning efficiency => higher intensity can be tolerated • Smaller gaps in the whole hierarchy => a smaller aperture can be protected, and thus a smaller β* can be used • Goal of MD: • Drive collimators to nominal 3.5 TeV settings and continue towards nominal 7 TeV settings • Check cleaning performance with loss maps • While the collimators are moved, monitor tune shifts in the background • Two fills used

  3. Results from first fill • B1 collimators driven to nominal 3.5 TeV settings • Tried to push further towards nominal 7 TeV settings in mm (TCP at 4 sigma at 3.5 TeV) • Hierarchy breakdown observed when moving in secondary collimators • New tight settings with larger retraction between primary and secondary invented on the spot to keep hierarchy • These settings successfully qualified with loss maps • B2 stayed at nominal 3.5 TeV settings. Qualified successfully with loss maps

  4. Results from second fill • Pushed B2 further in towards nominal 7 TeV settings. Could push further than B1, but had to retract secondary collimators by 0.3 σ to keep hierarchy. Successfully qualified with loss maps. • Kept B1 at nominal 3.5 TeV settings and made loss maps. Hierarchy breakdown observed! B1 nominal B2 nominal

  5. Impedance measurements • Tune shifts (few 1e-4) observed when moving in and out groups of collimators • Preliminary estimate: transverse impedance from vertical tune shifts 4-9 MΩ/m • Ongoing analysis to compare with predictions • Measured signals noisy. New measurements with transverse damper off useful Impedance team

  6. Achieved improvements • Local cleaning inefficiency in Q8 downstream of IR7 improved by about an order of magnitude with tight settings (though increase at Q7 – showers?) • We can squeeze more at IPs when collimators closer to beam. Smaller β* possible. • Further analysis needed for final conclusions. Can we move in TCTs? D. Wollmann Tight settings Nominal settings • Is it possible to operate with tight settings in physics fills? Impedance? Life time?

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