ILC DR instability simulations CMAD a tracking and e-cloud beam instability parallel code (M.P. SLAC) Taking MAD(X) optics file at input, thus tracking the beam in a real lattice and applying the interaction beam-electron cloud over the whole ring refined simulations: finding density thresholds 1.7e11 e/m3 for DCO4 and 3.5e11 e/m3 for DSB3 DC04 lattice: 6.4 km ring DSB3 lattice: 3.2 km ring (M. Pivi, SLAC)

Tune shift DCO4 CMAD

Tune shift DCO4 No cloud

Tune shift DCO4 1.2e10 e/m3

Tune shift DCO4 1.2e11 e/m3

Tune shift DCO4 CMAD All combined

2006 Recommendation

Base for Recommendation By March we were asked to give a recommendation on the reduction of the ILC DR circumference to 3 km while maintaining the same 6ns bunch spacing and address the electron cloud instability We have used 3 simulation codes ECLOUD, POSINST (CLOUDLAND) to predict the build-up and 1 code CMAD to predict the beam instability threshold for the 6km and 3km Damping Rings, namely DCO4 and DSB3. The codes are currently used for CesrTA simulations. Simulations were performed by the international collaboration in particular at Frascati, Cornell, LBNL and SLAC, from September 2009 to March 2010. 8

Recommendation Summary: given the same current and bunch distance we expect similar or even higher instability threshold for the shorter ring With respect to RDR baseline, the risk level to adopt a reduced 3km Damping Ring while maintaining the same bunch spacing is low. 9

Wrap up simulation results by next Webex meeting In preparation for recommendation of ILC Damping Ring length, proposing a Webex meeting before LCWS10: Tuesday March 23