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M. Pivi

International Linear Collider DR electron cloud R&D effort: Clearing electrode and triangular fin. M. Pivi

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M. Pivi

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  1. 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

  3. E-cloud and SEY R&D Program SLAC • 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

  4. Projects ONGOING TESTS AT SLAC: ONGOING PROJECTS:

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

  6. Clearing of electron cloud in ILC dipole magnet The width of low electron density region increases with the size of the electrode. 100 Voltage 0 Voltage Clearing field 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. L. Wang, SLAC June 2006

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

  8. Curved clearing electrodes effect Assume electron at rest near wall before bunch pass. Electron is first accelerated by the beam to the center chamber and then attracted backby 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 ! + 100 V During the spacing between bunches: (ECE = cl. electrode field near wall)

  9. SuperB and ILC DR Compare electron cloud in SuperB and ILC Difference in bunch spacing: SUPERB=1.5 ns and ILC=6.15 ns Mar 2006

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

  11. ECL2 Workshop CERN, March 2007 Enamel • 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 • Universal dissolver for anorganic, metallic oxides • Countless possibilities of variaty • Generally free from any organic material

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

  13. Layout installation – in PEP-II f3.5” f1.73” reduction to ILC DR chamber diameter Chamber cross section 4-bend chicane ~25” 59” 22” (D-BOX) (D-BOX) BEND BEND BEND BEND Grooved chamber(?!) Clearing electrode chamber tapered chamber 2 tapered chamber 1 spool chamber D-BOX=diagnostic box, electron detection centered on BEND and 13.5” long

  14. Sketch clearing electrode chamber and diagnostic Electron cloud diagnostic R. Macek LANL • 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 ” max: 5” M. Pivi SLAC -February 13, 2007

  15. Test Chamber Assembly, 1.5M Long (59.00”) Vacuum Tube, 3.75 OD x 3.51 ID 3.375” CFF, Rotatable Vacuum Tube, 4.00 OD x 3.50 ID Collector Port Flange 3.375” CFF, Non-Rotatable Tube, 2.00” OD x 1.73” ID Flange to Flange Length = 59.00” 1.33” CFF access port Feedthrough, Ceramtec #1084-01-W Mounted to 1.33” CFF

  16. 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”

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

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

  19. Dimensions: LTOT630 mm LTAP115mm Rpipe=44 mm =60 deg h1,h3,h3=5 mm t=2 mm 2nd Geometry: 1 Ports 50 Ohm 1st Geometry: 2 Ports 50 Ohm LTOT Rpipe 1 David Alesini, Frascati, Feb 2007 t h3 h1 First discontinuity h2 LTAP

  20. HFSS Results on Copper electrode stainless steel chamber D.Alesini, LNF, Frascati A. Krasnykh, SLAC, Mar 2007 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

  21. 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.

  22. Projects ONGOING TESTS AT SLAC: ONGOING PROJECTS:

  23. L. Wang, SLAC

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

  25. Smoother tips spoil effectiveness of grooves (POSINST) • Spoiling effect of smooth groove-tips can be compensated by making the grooves deeper. • Generally, 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 hg Max of cloud density vs. height hg for 3 choices of groove-tip radius

  26. 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.

  27. Triangular groove chamber

  28. 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

  29. Self-consistent code development Dynamics • MAD input lattice • Tracking 1 bunch in the ring lattice by 2nd 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]

  30. CMAD status Completed. Single-bunch instability part: studies ongoing. Build-up electron cloud to be added, vacuum chamber, SEY, etc. Use POSINST now ns=0.067 e- density 1e10 e/m3 macrop=100000 Electron cloud distribution in bends and straights (so far from POSINST) First results: few synchrotron oscillation periods (9min * 320 CPUs / turn) CMAD tracking, ILC DR beam at extraction, with average cloud density 1e10 e/m3 (below threshold). Bottleneck => in ILC DR, beam aspect ratio reaches sx/sy=200, demanding Particle in Cell grid ratios num-gridx >> num-gridy, to correctly simulate Electric field.

  31. 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

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