ILC Damping Ring electron cloud WG effort Mauro Pivi SLAC on behalf of ILC DR working group on e- cloud ILC DR Webex Meeting Jan 3, 2010

ILC DR Working Group goals Goals of the LC DR Working Group are: To give a recommendation on the feasibility of a shorter damping ring by comparing the electron cloud build-up and instability for the 6.4km and 3.2km rings with a 6 ns bunch spacing by March 2010, then Following the CesrTA program, working to give our recommendation on e- cloud mitigations and evaluate the electron cloud in the shorter 3.2 km ring with a 3 ns bunch spacing (on hold: pending decision on 3 ns) Furthermore starting later in 2010, to fully integrate the CesrTA results into the Damping Ring design.

ILC DR Working Group - Deliverables Recommendation for the reduction of the ILC Positron Damping Ring Circumference By March 2010 Recommendation for the baseline and alternate solutions for the electron cloud mitigation in various regions of the ILC Positron Damping Ring. Following CesrTA program

ilc-DR 6.4 Km, 6 ns bunch spacing*. Build Up Input Parameters for ECLOUD ilc-DR 6.4 Km, 6 ns bunch spacing*. Bunch population Nb 2.1x1010 Number of bunches 45 x 8 trains Bunch gap Ngap 15 Bunch spacing Lsep[m] 1.8 Bunch length σz [mm] 6 Bunch horizontal size σx [mm] 0.26 Bunch vertical size σy [mm] 0.006 Photoelectron Yield Y 0.1 Photon rate (g/e+/m) at arc walls dn /ds 0.33 Antechamber protection  Scan: 90% - 99% Fraction of uniformly distributed e- at the wall R Scan: 15% - 25% Max. Secondary Emission Yeld δmax Scan: 0.9 - 1.4 Energy at Max. SEY Εm [eV] 300 SEY model Cimino-Collins ((0)=0.5) *https://wiki.lepp.cornell.edu/ilc/pub/Public/DampingRings/WebHome/DampingRingsFillPatterns.xls

e-cloud “distribution” - 6km ring SEY=0.9 SEY=1.2 SEY=1.4 Snapshot of the cloud distribution in dipole “just before” the passage of the last bunch for: R=25%, =90% Theo Demma, LNF

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 New simulations: finding higher threshold in DCO4 then in previous DCO2 lattice (in DCO2 we set at input 10% beam jitter that lowered threshold..) DC04 lattice: 6.4 km ring DSB3 lattice: 3.2 km ring AVERAGE RING DENSITY (M. Pivi, SLAC)

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 New simulations: finding higher threshold in DCO4 then in previous DCO2 lattice (in DCO2 we set at input 10% beam jitter that lowered threshold..) DC04 lattice: 6.4 km ring DSB3 lattice: 3.2 km ring DENSITY IN MAGNETS (M. Pivi, SLAC)

Summary WG collaboration: running new campaign of build-up and beam instability simulations for latest DCO4 and DSB3 lattices Build-up simulations: preliminary, SEY=1.2 appears to be a safe value for the 6.4km DR Given the same current and bunch distance we expect similar or even higher instability threshold for the shorter ring Instability simulations. Found strong dependence on beam jitter in ILC DR: 10% sy beam offset can lower instability threshold by factor ~2 On track for March recommendation. Still needed: build-up simulations in wigglers (and quadrupoles)