3 February 2010

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

3 February 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.

3 February 2010

ILC DR Working Group - Deliverables

Recommendation for the reduction of the ILC Positron Damping Ring Circumference

Recommendation for the baseline and alternate solutions for the electron cloud mitigation in various regions of the ILC Positron Damping Ring.

By March 2010

Following CesrTA program

4

Build Up Input Parameters for ECLOUD

Bunch population Nb 2.1x1010

Number of bunches Nb 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 (/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)

ilc-DR 6.4 Km, 6 ns bunch spacing*.

*https://wiki.lepp.cornell.edu/ilc/pub/Public/DampingRings/WebHome/DampingRingsFillPatterns.xls

5

e-cloud “distribution” - 6km ring

Snapshot of the cloud distribution in dipole “just before” the passage of

the last bunch for: R=25%, =90%

SEY=1.4

SEY=0.9 SEY=1.2

Theo Demma, LNF

3 February 2010

• 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..)

ILC DR instability simulations

(M. Pivi, SLAC)

DC04 lattice: 6.4 km ring DSB3 lattice: 3.2 km ring

AVERAGE RING DENSITY

3 February 2010

• 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..)

ILC DR instability simulations

(M. Pivi, SLAC)

DC04 lattice: 6.4 km ring DSB3 lattice: 3.2 km ring

DENSITY IN MAGNETS

3 February 2010

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% y beam offset can lower instability threshold by factor ~2

• On track for March recommendation. • Still needed: build-up simulations in wigglers (and

quadrupoles)