9-12 April 2007 International Linear Collider DR electron cloud R&D effort: Clearing electrode and triangular fin M. Pivi T. Raubenheimer, J. Seeman, T. Markiewicz, R. Kirby, F. King, B. McKee, M. Munro, D. Hoffman, G. Collet, L. Wang, A. Krasnykh, D. Arnett, (SLAC) M. Venturini, M. Furman, D. Plate (LBNL), D. Alesini (LNF Frascati), R. Macek (LANL) ECLOUD 07 Daegu, S. Korea

2 Milestones to the ILC Engineering Design Report (EDR) 1. Characterize electron-cloud build-up. (Very High Priority) 2. Develop electron-cloud suppression techniques. (Very High Priority) Priority: characterize coating techniques and testing of conditioning and recontamination in situ. Clearing electrodes concepts by installation of chambers in accelerators. Characterization of impedance, HOM and power load deposited to the electrodes. Groove, slots and other concepts. Characterization of impedance, and HOM. 3. Develop modeling tools for electron-cloud instabilities. (Very High Priority) 4. Determine electron-cloud instability thresholds. (Very High Priority) Characterization the electron cloud instability: various codes in use PETHS, HEAD-TAIL, WARP/POSINST, CMAD

R&D Goals: –Estimate e-cloud build-up and single-bunch instability thresholds –Reduce surface secondary electron yield (SEY) below electron cloud threshold for ILC DR: SEY ≤ 1.2 Surface approaches –Thin film coatings –Electron and photon surface conditioning –Clearing electrodes –Grooved surfaces Projects: –ONGOING: conditioning TiN and NEG coatings in PEP-II straights –ONGOING: rectangular groove chambers in PEP-II straights –PLANNED: clearing electrode chamber in magnets –PLANNED: triangular groove chamber in magnets E-cloud and SEY R&D Program SLAC

ONGOING TESTS AT SLAC: Projects CLEARING ELECTRODES BEND…end 2007Design FINS TRIANG.BEND…end 2007Design TEST inLOCATIONReady for INSTALLATION Status SEY TESTSSTRAIGHTPEP-II LER PR12November 2006 Ready FINS RECTANG.STRAIGHTPEP-II LER PR12November 2006 Coating of extruded Al chambers ONGOING PROJECTS:

Clearing Electrode Concept of a clearing electrode Model: Wire (Rod) type L.Wang et al., EPAC2006 Beam duct Rod (Electrode) Ceramics Support Feed-through Ceramics Support with thin metal coating Beam 2007/03/1-2 Y. Suetsugu KEK - ECL2 CERN 28

Clearing of electron cloud in ILC dipole magnet Clearing field (left) and effect (right) of a traditional stripline type of electrode. The red color in (left) shows the electrode. The blue and black dots in right plot show the electrons with different size of electrode. The width of low electron density region increases with the size of the electrode. Clearing field 0 Voltage 100 Voltage L. Wang, SLAC June 2006

Simulation unsing POSINST code of electron cloud build-up and suppression with clearing electrodes. ILC DR positron 6 km ring. Curved clearing electrodes: simulations BEND chamber with curved clearing electrodes M. Pivi – P. Raimondi, L. Wang, T. Raubenheimer SLAC, Mar 2006

Curved clearing electrodes effect V Assume electron at rest near wall before bunch pass. Electron is first accelerated by the beam to the center chamber and then attracted back by the biased +100V electrode. Electron back to the wall after 3 ns, much before the next bunch passage.  Electron cloud build-up is strongly suppressed ! During the spacing between bunches: (E CE = cl. electrode field near wall)

Only one electrode polarized. Single electrode M. Pivi – P. Raimondi, SLAC, Mar 2006

SuperB and ILC DR LatticeSUPERBOCS Circumference [m]6114 Energy [GeV]5.066 Harmonic number13256 Bunch charge [10 10 ]2.0 Bunch Spacing [ns] Mom. comp. [10 -4 ]1.62 Bunch length [mm] sigz6.0 Sigx, sigy in BEND [  m] 620, 8 Energy spread [10 -3 ]1.29 Synchrotron Tune [10 -2 ]3.37 Compare electron cloud in SuperB and ILC Difference in bunch spacing: SUPERB=1.5 ns and ILC=6.15 ns Mar 2006

SUPERB bends clearing electrodes POSINST code Near beam electron cloud density. M. Pivi – P. Raimondi, L. Wang, T. Raubenheimer SLAC, Mar 2006 E-cloud build-up and suppression with/without clearing electrodes in bends of SUPERB factory (bs=1.54ns) Compare electron cloud in SuperB and ILC Difference in bunch spacing: SUPERB=1.5 ns and ILC=6.15 ns Compare electron cloud in SuperB and ILC Difference in bunch spacing: SUPERB=1.5 ns and ILC=6.15 ns

Clearing electrodes R&D Suppress the electron cloud in BEND and WIGGLER (QUAD) section: Perfect ! Prototypes installation in LHC test dipole.. CERN ad Texas Univ. stripe electrode design. Warning: ion-clearing electrodes (alumina) in Daphne generate impedance and overheating, need to be removed. Control the generation of HOM, transverse impedance, resistive wall impedance and RF heating. Optimized design should be tested in beam line with similar beam parameters  R&D at PEP-II, Cornell, KEK, CERN. LHC electrode design

Enamel Vitreous material, generated in melting process, contents a number of anorganic and oxidic-silicatic fractions Vitreous material, generated in melting process, contents a number of anorganic and oxidic-silicatic fractions Melting on metal- or glassubstrate, chemical and micromechanical connection between the layer and metall surface Melting on metal- or glassubstrate, chemical and micromechanical connection between the layer and metall surface Universal dissolver for anorganic, metallic oxides Universal dissolver for anorganic, metallic oxides Countless possibilities of variaty Countless possibilities of variaty Generally free from any organic material Generally free from any organic material ECL2 Workshop CERN, March 2007

double enamel coating – the new e- cloud killer (F. Caspers, F.-J. Behler, P. Hellmold, J. Wendel) ECL2 Workshop CERN, March 2007

59”~25” tapered chamber 1   3.5”   1.73” Grooved chamber(?!) Clearing electrode chamber spool chamber Layout installation – in PEP-II (D-BOX) tapered chamber 2 BEND D-BOX=diagnostic box, electron detection centered on BEND and 13.5” long Chamber cross section 22” (D-BOX) BEND reduction to ILC DR chamber diameter 4-bend chicane

Sketch clearing electrode chamber and diagnostic Electron cloud diagnostic R. Macek LANL max: 5” Test chamber with clearing electrodes Test chamber in PEP-II in a special chicane with 4 identical magnets magnets: SLC Final Focus correctors Chamber aperture constraint from the magnet aperture: max 5 ” M. Pivi SLAC -February 13, 2007

Test Chamber Assembly, 1.5M Long (59.00”) Vacuum Tube, 4.00 OD x 3.50 ID Vacuum Tube, 3.75 OD x 3.51 ID 3.375” CFF, Non-Rotatable Feedthrough, Ceramtec # W Mounted to 1.33” CFF 3.375” CFF, Rotatable Tube, 2.00” OD x 1.73” ID Flange to Flange Length = 59.00” Collector Port Flange 1.33” CFF access port

Test Chamber with Electrode Electrode, Copper 0.063” x ~1.0” x 50.0” (49.606” between feedthrough centers) Clearance between Electrode and chamber Varies between.070” and.080”

Electrode Connection Space between chamber and electrode = 0.08” (2mm all around)

Electrode Connection Collector Port, 20.00” x 1.00” Collector Port Flange, 21.50” x 2.50” 0.125” Dia. Holes

R pipe 11 h3 t L TOT L TAP h1 h2 First discontinuity Dimensions: L TOT  630 mm L TAP  115mm Rpipe=44 mm  =60 deg h1,h3,h3=5 mm t=2 mm 1st Geometry: 2 Ports 50 Ohm 2nd Geometry: 1 Ports 50 Ohm David Alesini, Frascati, Feb 2007

A. Krasnykh, SLAC, Mar 2007D.Alesini, LNF, Frascati HFSS Results on Copper electrode stainless steel chamber Longitudinal Impedance: power deposited to electrode ~10W with PEP-II beam, and ~2W for ILC DR beam. Add Synchrotron radiation in PEP-II +40W  power load 50W onto electrode

Summary clearing electrodes Clearing electrode/s suppress cloud build-up and perfectly eliminate the cloud at center beam. Concern: Removal of power load from clearing electrode! Stripe line kicker design tests first Clearing electrode on isolator substrate: “enamel” more studies needed.

ONGOING TESTS AT SLAC: Projects CLEARING ELECTRODES BEND…end 2007Design FINS TRIANG.BEND…end 2007Design TEST inLOCATIONReady for INSTALLATION Status SEY TESTSSTRAIGHTPEP-II LER PR12November 2006 Ready FINS RECTANG.STRAIGHTPEP-II LER PR12November 2006 Coating of extruded Al chambers ONGOING PROJECTS:

L. Wang, SLAC

Note: fin chambers needed in magnet regions covering ~12% of the ILC DR

27 M. Venturini, M. Furman LBNL 20 Feb Smoother tips spoil effectiveness of grooves (POSINST) ãSpoiling effect of smooth groove-tips can be compensated by making the grooves deeper. ãGenerally, a finite groove-tip radius enhances dependence of groove effectiveness on groove height Max of cloud density vs. groove-tip radius for two groove height h g Max of cloud density vs. height h g for 3 choices of groove-tip radius

Summary triangular fins in magnetic field regions Triangular groove are very promising at reducing the electron cloud build-up in bends and wigglers. In magnets, reduced groove area needed only on top and bottom chamber. Photons leave the chamber more efficiently (<< lower accumulation of photoe- than with a uniform groove distribution around chamber perimeter) Sharpness of tips important to reduce SEY.

Triangular groove chamber

Self-consistent code CMAD At SLAC, developing self-consistent code including simulation of cloud build-up and beam instabilities. Parallel computation allows tracking the beam in a MAD lattice, instability studies, threshold SEY, dynamic aperture study, frequency map analysis, tune shift computation.. MAD deck to track beam with an electron cloud in the ILC DR. Bunch at injection

Self-consistent code development Dynamics MAD input lattice Tracking 1 bunch in the ring lattice by 2 nd order transport maps (R, T) –Not symplectic (but 99% phase space conservation if ILC DR 500 turns) Tracking 6D beam phase space, 3D beam dynamics 3D electron dynamics Apply beam-cloud interaction at each element of MAD lattice 2D forces beam-cloud, cloud-cloud computed at interaction point Electron dynamics: cloud pinching and magnetic fields included Approximations: Assign same cloud distribution and density for each class of elements (ex: 1E+12 em -3 in quadrupoles, 4E+12 em -3 in wigglers) Evolution of cloud build-up updated at each beam turn (weak beam changes turn by turn) – [NOTE: cloud build-up part is not included yet] If beam sizes are identical at two elements, apply earlier computed cloud- to-beam kick – [switched OFF]

CMAD status First results: few synchrotron oscillation periods (9min * 320 CPUs / turn) CMAD tracking, ILC DR beam at extraction, with average cloud density 1e10 e/m 3 (below threshold). Electron cloud distribution in bends and straights (so far from POSINST) Completed. Single-bunch instability part: studies ongoing. Build-up electron cloud to be added, vacuum chamber, SEY, etc. Use POSINST now Bottleneck => in ILC DR, beam aspect ratio reaches  x/  y=200, demanding Particle in Cell grid ratios num-gridx >> num-gridy, to correctly simulate Electric field. s =0.067 e- density 1e10 e/m 3 macrop 

Summary Latest results (SLAC/KEK) of direct measurements in B-factories beam line indicate very low SEY for thin film coatings. R&D effort for ILC DR on development of coating mitigation techniques + antechamber design In parallel, R&D studies should continue for other possible mitigation techniques (ILC DR upgrade, SuperB) Simulations: clearing electrodes are most efficient at eliminating rather than just reducing the electron cloud - actual concern: remove power on clearing electrodes