Electron Cloud in ilcDR: Update T. Demma, INFN-LNF

Electron cloud buildup simulation Cloud buildup was calculated by code “ECLOUD” developed at CERN. Assumptions: - Round Chambers - A fraction R of the primary electrons are uniformly produced on chamber wall. - A reduced number of primary electrons is artificially used in order to take into account the reduction of electron yield by the ante-chamber: where: dn/ds is the average number of emitted photons per meter per e+, Y is the quantum efficiency, and  is the percentage of photons absorbed by the antechambers.

Estimation of antechamber protection in ILC-DR In order to calculate the number of photons that remain inside the chamber, we must integrate the fundamental spectrum of synchrotron radiation The calculation is done by numerical integration taking into account the geometry of the chamber and the curvature of the orbit (extrapolated from mad lattice files: https://wiki.lepp.cornell.edu/ilc/bin/view/Public/DampingRings/WebHome). Very preliminary estimate for ILC-DR DCO4 lattice indicate that only ~2% of the radiated photons remain inside the chamber (to be double checked)

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 (e-/e+/m) dn /ds 0. 204 Antechamber protection  90%; 97% 99% Fraction of uniformely dist photelectrons R 15% 20% 25% Max. Secondary Emission Yeld δmax 0.9 1.2 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

Average e-cloud density in ILC-DR dipole (SEY=0.9;1.2;1.4) =90% R=25% =97% R=25% =99% R=15% =90% R=15% =97% R=15% =99%

e-cloud “distribution” SEY=0.9 SEY=1.2 SEY=1.4 Snapshot of the cloud distribution “just before” the passage of the last bunch for: R=25%, =90%

Average e-cloud density SEY=1.2 =90%; =97%; =99% R=25% =90%; =97%; =99%

Average e-cloud density SEY=1.2, R=20% =90%; =97%; =99%

Average vs central density SEY=1.2, R=20%,=90% t[sec] Red dots mark e-cloud density near the beam (+ -10 sig.) evaluated “just before” the passage of each bunch.

Comparison with bruns Average Central Dopo il passaggio di 150 bunches consecutivi con pey=10-4, sey=1.1, R=99.9%, bunch spacing=0.94 m. Lui si trova una densità di 2*1011, ci siamo vicini soprattuto con la central. Comunque aspetto che finisca la simulazione mi mancano ancora 150 bunches. Le gap nel treno sono importanti!!!!