The effects of the beam-beam interaction on the coherent motion of the barycentres of the colliding bunches are considered for asymmetric (two-ring) e+e− colliders, where circumference, energy, tune, etc. may be different between two rings. As well as integer and half-integer resonances, sum resonances occur. These resonances may be quite dense in the tune diagram, for the cases with different circumferences. This effectt poses a severe restriction on the choice of the circumference ratio. On these resonances, the beams separate spontaneously at the interaction point. In particular, on the sum resonance, the barycentres follow a limit cycle in four-dimensional phase space, rather than reaching a fixed point. This causes a severe drop in the luminosity. Results of analytical calculations and computer simulations for the motion of the barycentres and the excitation of the resonances are presented.
雑誌名
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Barycentre motion of beams due to beam-beam interaction in asymmetric ring colliders
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