1. 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

2. 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.

3. 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

4. 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:
Energy at Max. SEY
Εm [eV]
300
SEY model
Cimino-Collins ((0)=0.5) *

5. 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

6. 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)

7. 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)

8. 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)