Electron Cloud & IBS Update T. Demma, INFN-LNF SuperB General Meeting October 6-9 2009, SLAC

Plan of Talk Electron Cloud Effects Electron Cloud Single Bunch Instability Simulations Electron Cloud Build-Up Dipole Quadrupole Mitigation Techniques e-cloud summary IBS

SuperB Configuration Options LER/HER Unit June 2008 Jan. 2009 March 2009 Sep. 2009 E+/E- GeV 4/7 4.18/6.7 L cm-2 s-1 1x1036 I+/I- Amp 1.85 /1.85 2.00/2.00 2.80/2.80 2.12/2.12 Npart x1010 5.55 /5.55 6/6 4.37/4.37 6.33/4.06 Nbun 1250 2400 1011 q/2 mrad 25 30 bx* mm 35/20 20/20 by* 0.22 /0.39 0.21 /0.37 0.2 /0.32 ex nm 2.8/1.6 2.6/1.6 ey pm 7/4 sx 9.9/5.7 5.7/9.05 sy 39/39 38/38 36/36 sz 5/5 xx X tune shift 0.007/0.002 0.005/0.0017 0.004/0.0013 xy Y tune shift 0.14 /0.14 0.125/0.126 0.091/0.092 RF stations 5/6 5/8 RF wall plug power MW 16.2 18 25.5 Circumference m 1800

Simulation of single-bunch instability Simulations were performed using CMAD (M.Pivi): Parallel bunch-slices based decomposition to achieve perfect load balance Beam and cloud represented by macroparticles Particle in cell PIC code 9-point charge deposition scheme Define at input a cloud density level [0<r<1] for each magnetic element type Tracking the beam (x,x’,y,y’,z,d) in a MAD lattice by 1st order and 2nd (2nd order switch on/off) transport maps MAD8 or X “sectormap” and “optics” files as input Apply beam-cloud interaction point (IP) at each ring element Input parameters (Sep.09 conf.) for CMAD Beam energy E[GeV] 6.7 circumference L[m] 1370 bunch population Nb 5.74x1010 bunch length σz [mm] 5 horizontal emittance εx [nm] 1.6 vertical emittance εy [pm] 4 hor./vert. betatron tune Qx/Qy 40.57/17.59 synchrotron tune Qz 0.01 hor./vert. av. beta function 20/20 momentum compaction  4.04e-4

Emittance growth due to fast head-tail instability (LNF conf.) =7x1011e-/m-3 <5x1011e-/m-3 The interaction between the beam and the cloud is evaluated at 40 different positions around the SuperB HER (LNF option) for different values of the electoron cloud density. The threshold density is determined by the density at which the growth starts:

Bunch shape at last turn Above instability threshold Below instability threshold

Beam losses =3x1011e-/m-3; =7x1011e-/m-3 Hor. Bunch centroid oscillations Particles per bunch vs. time Ver. Bunch centroid oscillations =3x1011e-/m-3; =7x1011e-/m-3

Electron cloud buildup simulation Cloud buildup was calculated by code “ECLOUD” developed at CERN. Assumptions: - Round or elliptical Chambers - Uniform production of primary electrons 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.

Build Up Input Parameters for ECLOUD Bunch population Nb 4.2x1010 Number of bunches nb 500 Bunch spacing Lsep[m] 1.2 Bunch length σz [mm] 5 Bunch horizontal size σx [mm] 0.3 Bunch vertical size σy [mm] 0.012 Photoelectron Yield Y 0.2 Photon rate (e-/e+/m) dn /ds 0.72 Photon Reflectivity R 100% Max. Secondary Emission Yeld δmax 1.0-1.2 Energy at Max. SEY Εm [eV] 250 SEY model Cimino-Collins ((0)=0.5)

Buildup in the SuperB arcs: Dipoles By=0.3 T; =95% SEY=1.1 SEY=1.2 SEY=1.3 SEY=1.4 Snapshot of the electron (x,y) distribution “just before” the passage of the last bunch

Electron Cloud Density at Center of Beam Pipe Center e-cloud density for =95% SEY=1.1 SEY=1.2 SEY=1.3 Center e-cloud density for = 99% SEY=1.1 SEY=1.2 SEY=1.3

Buildup in the SuperB arcs: Quadrupoles LER Arc quadrupole vacuum chamber (CDR) dBy/dx=2.5T/m, =99% max=1.2 average center Snapshot of the electron (x,y) distribution “just before” the passage of the last bunch

Head-Tail Instability Threshold June 2008 January 2009 March 2009 int [1015m-2] solenoids int [1015m-2] no solenoids SEY=1.1 95% 0.06 2.1 0.09 2.5 0.22 2.7 99% 0.02 0.25 0.04 0.3 0.7 SEY=1.2 2.8 0.27 3.2 0.45 6.5 0.045 0.71 0.82 0.07 2.4 SEY=1.3 20.2 2.9 25.7 5.4 25 0.94 1.3 4.1 4.5 13 Sep.2009 int [1015m-2] solenoids 0.1 0.07 0.3 2.0 0.7 Instability occurs if: where cent. ande,th are obtained from simulations. LNF conf.

Drift Mitigation Summary Plots show average of all collectors for all drift RFAs In general, the most cloud is seen in the bare Al chambers (blue) Much less in copper chambers (black) Less still in coated chambers TiN: green Carbon: red e- e+ J.Calvey (Cornell) CesrTA Mitigation Studies: LCWA09 CesrTA Mitigation Studies: LCWA09

Drift Mitigation Summary II Same plots as last slide, but not normalized to photon flux Al is still by far the worst, but normalization makes some difference in the relative strength of the signal in the other chambers Current calculation of photon flux assumes no reflections A new synchrotron radiation program, which will include reflections, is under development e- e+ J.Calvey (Cornell) CesrTA Mitigation Studies: LCWA09 CesrTA Mitigation Studies: LCWA09

Chicane Current Scan Current scan, 1x45 e+, 14ns, 5GeV Both mitigation techniques show drastic improvement relative to Aluminum Note that Al signal is divided by 20 Al shows significant mutipacting TiN actually seems to saturate Groove + TiN is even better than just TiN J.Calvey (Cornell) CesrTA Mitigation Studies: LCWA09 CesrTA Mitigation Studies: LCWA09

Clearing Electrode Results Y. Suetsugu (KEK) Results Drastic decrease in the electron density by applying Velec was observed. The electron density decreased to less than 1/100 at Velec > ~+300 V 1585 bunches (Bs ~ 6 ns) 6x10-7 6x10-9 2009/10/1 2009/10/1 LCWA09, Albuquerque LCWA09, Albuquerque 17

Groove structure Result Y. Suetsugu (KEK) Result The electron density decreased to 1/6~1/10 compared to the case of a flat surface. [5 mm groove] Flat Groove 1585 bunches (Bs ~ 6 ns) Vr = 0 V [Linear scale] 4x10-7 4x10-7 Center 2009/10/1 2009/10/1 LCWA09, Albuquerque LCWA09, Albuquerque 18

Clearing electrodes for DAFNE D.Alesini, A.Battisti, R. Sorchetti, V. Lollo (LNF)

Clearing electrodes installation: Wigglers D.Alesini, A.Battisti, R. Sorchetti, V. Lollo (LNF)

Electrodes Field and e-Cloud build-up Simulation unsing POSINST code of electron cloud build-up and suppression with clearing electrodes.

e-cloud summary Simulations indicate that a peak secondary electron yield of 1.2 and 99% antechamber protection result in a cloud density close to the instability threshold. Planned use of coatings (TiN, ?) and solenoids in SuperB free field regions can help. Ongoing studies on mitigation techniques (grooves in the chamber walls, clearing electrodes) offers the opportunity to plan activity for SuperB. • Work is in progress to: estimate other effects: multi-bunch instability, tune-shift, ... compare the results with other codes (PEHTS, PEI, K.Ohmi; POSINST, M.Furman,M.Pivi). Needs: more cpu power to track single bunch instability through a real lattice. “stable” set of ring parameters.

Bane's approximation K. Bane, “A Simplified Model of Intrabeam Scattering,” Proceedings of EPAC 2002, Paris (Fr.).

Calculations procedure Evaluate equilibrium emittances ei and radiation damping times ti at low bunch charge Evaluate the IBS growth rates 1/Ti(ei) for the given emittances, averaged around the lattice, using K. Bane approximation (EPAC02) Calculate the "new equilibrium" emittance from: For the vertical emittance use* : where r varies from 0 (y generated from dispersion) to 1 (y generated from betatron coupling) Iterate from step 2 * K. Kubo, S.K. Mtingwa, A. Wolski, "Intrabeam Scattering Formulas for High Energy Beams," Phys. Rev. ST Accel. Beams 8, 081001 (2005)

SuperB parameters Sep. 09 configuration HER LER IP E[Gev] h[nm] v [pm] s [mm] p/p h/ s [ms] HER 6.7 1.6 4 5 6.15e-4 30/15 LER 4.12 2.6 7 6.57e-4 40/20

IBS in SuperB HER Sep.09 configuration gr.~9% gr.~9% gr.~7% gr.~4% gr.~4%

IBS in SuperB LER Sep.09 configuration gr.~19% gr.~18% gr.~16% gr.~7% gr.~7%

Recovering nominal emittance in LER gr.~24% same optics smaller emittance

Parameters & IBS S. Siniatkin (BINP) Parameter Unit Value Input data Energy GeV 4.18 Number of particle 5.7*1010 Hor. Emmitance Em_x0 nm*rad 2.2 Coupling % 0.25 Energy spread dE_0 6.57*10-4 Damping time x / y / s msec 44 / 44 / 22 Length Sigma_s0 mm 5 Voltage RF MV 4.1 fRF MHz 475.8 Bucket RF 2.22 Result[1,2] Ratio Em_x_IBS/Em_x0 1.23 Ratio dE_IBS/dE_0 1.11 S. Siniatkin (BINP)

IBS Summary The effect of IBS on the transverse emittance is reasonably small for both rings in the Sep. 09 configuration An interesting study: develop a MonteCarlo code to study the beam size distribution in the presence of IBS

Changing behavior of Twiss function - increasing separation between horizontal and vertical beta functions. It is result to changing of compensation sextupole scheme; Fig.8 S. Siniatkin (BINP)

Electron Cloud Effects The electron cloud develops quickly as photons striking the vacuum chamberwall knock out electrons that are then accelerated by the beam, gain energy, and strike the chamber again, producing more electrons. The peak secondary electron yield (SEY) of typical vacuum chamber materials is >1 even after surface treatment, leading to amplification of the cascade. The interaction between the electron cloud and a beam leads to the electron cloud effects such as single- and multi-bunch instability, tune shift, increase of pressure and so on.