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High Luminosity LHC Project
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Crab cavities - How does it work ?
Suppression of a beam instability by bringing the beams into collision more quickly
If the two counter-rotating beams are separated by a transverse offset between one and two rms beam sizes for too long a time, an impedance-induced beam instability can develop due to a loss of transverse Landau damping.
Mode-cility of cooupling instablliding beams suppressed by the hourglass effect
The strong focalization of the beam at the interaction points leads to a deformation of the beam profile due to the hourglass effect, which suppresses the mode-coupling instability between beam-beam and impedance through Landau damping => Please note that the hourglass effect (seen on the right picture) has been amplified to see it more clearly BUT the stabilising effect was observed with the correct HL-LHC parameters.