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Some results on the LHC multibunch modes at 7 TeV/c

Some results on the LHC multibunch modes at 7 TeV/c. N. Mounet and E. M étral.

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Some results on the LHC multibunch modes at 7 TeV/c

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  1. Some results on the LHC multibunch modes at 7 TeV/c N. Mounet and E. Métral From Sacherer theory with the dipolar impedance (= the right impedance to put in a stability diagram) and synchrotron mode m=0, using a complete 25ns filling (3564 bunches), zero chromaticity and nominal LHC design parameters.

  2. Coupled-bunch modes from the beam screens only w.r.t all the machine elements in the model (Collimators + MBWs/MQWs magnets + beam screens + warm pipe + broad band) In horizontal, beam screens = 76% of the imaginary tune shift (i.e. -1/rise time), 2% of the real tune shift But pessimistic model of the beam screens in horizontal (used a factor 2 for the weld, see Carlo Zannini)

  3. Coupled-bunch modes from the beam screens only w.r.t all the machine elements in the model (Collimators + MBWs/MQWs magnets + beam screens + warm pipe + broad band) In vertical, beam screens = 72% of the imaginary tune shift (i.e. -1/rise time), 2% of the real tune shift

  4. Coupled-bunch modes from all the machine elements in the model: effect of the bunch length For the real tune shift, dependence in power law with a exponent of ~ -0.4

  5. Coupled-bunch modes from all the machine elements in the model: effect of the bunch length For the imaginary tune shift (= -1/rise time), small linear dependence

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