In $\mathrm{DA}\Phi \mathrm{NE}$, the Frascati $e^{+}/e^{-}$ collider, the crab waist collision scheme has been successfully implemented and tested during the years 2008 and 2009. During operations for the Siddharta experiment an unusual synchrotron damping effect induced by beam-beam collisions has been observed. Indeed, the positron beam becomes unstable above currents in the order of 200–300 mA when the longitudinal feedback is off. The longitudinal instability is damped by colliding the positron beam with a high current electron beam ($\sim 2\mathrm{A}$) and a shift of $\approx -600\mathrm{Hz}$ in the residual synchrotron sidebands is observed. Precise measurements have been performed by using both a commercial spectrum analyzer and the diagnostic capabilities of the $\mathrm{DA}\Phi \mathrm{NE}$ longitudinal bunch-by-bunch feedback. This damping effect has been observed in $\mathrm{DA}\Phi \mathrm{NE}$ for the first time during collisions with the crab waist scheme. Our explanation is that beam collisions with a large crossing angle produce longitudinal tune shift and spread, providing Landau damping of synchrotron oscillations.

• Received 22 November 2010

DOI:https://doi.org/10.1103/PhysRevSTAB.14.092803

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