On the Landau Damping and Decoherence of Transverse Dipole Oscillations
in Colliding Beams
Y.I. Alexahin
August 1996
Abstract:
Coherent transverse dipole oscillations in colliding head-on non-rigid bunches
are studied using the Vlasov equation. The corresponding eigenvalue problem is
solved numerically in the case of round Gaussian bunches of equal size but with
not necessarily equal intensities. Transition from the weak-strong to the
strong-strong cases is found at the intensity ratio of about 60% when a discrete
pi-mode frequency emerges from continuum of eigenfrequencies related to the beam-beam
tunespread in the weaker bunch. In the strong-strong case the large coherent beam-beam
tuneshift dominates over interchange processes between coherent and incoherent motion;
it can switch off Landau damping of dipole transverse oscillations, slows down
incoherent emittance growth due to external kicks on the beams.
The consequences for the transverse feedback operation in collision are discussed.
F. Ruggiero
Mon Apr 28 17:59:19 METDST 1997