1. ILC Damping Ring update on collective effect electron cloud R&D Mauro Pivi SLAC ILCDR06 Cornell Workshop September 26-28, 2006

2. p.2 Outline m Overview of the effect for different DR options m Status of experimental R&D m Mitigation techniques R&D plan m Simulations plan: what is left to do m Analysis m Conclusions m Secondary electron yield SEY

3. Compare options: simulations recent history Cloud density near (r=1mm) beam (m -3 ) before bunch passage, values are taken at a cloud equilibrium density. Solenoids decrease the cloud density in DRIFT regions, where they are only effective. Compare options LowQ and LowQ+train gaps. All cases wiggler aperture 46mm.

4. Need for mitigation Outstanding Questions about key remedies: 1) Is “conditioning” effective to stably decrease SEY < 1.2 ? 2) Fins: are fin-chambers viable to suppressing electron cloud in magnets ? 3) Clearing electrodes: is RF power load tolerable ? are impedance and HOM tolerable ? R&D: 1)Study conditioning in situ 2)Fin-chamber tests 3)Clearing electrodes chamber tests

5. An electron cloud generates if the metal surface secondary electron yield (SEY) is high enough for electron multiplication. In the ILC Damping Ring an electron cloud develop mostly in BENDS and WIGGLERS. Typically SEY <1.2 is required. R&D Goals –Reduce and stabilize the surface SEY below electron cloud threshold in the ILC damping ring. Challenge: SEY ≤ 1.2. Approaches –Electron and photon conditioning –Metal surfaces with fins (grooves) profile –Clearing electrodes Plan: –Measure the SEY of samples directly exposed to PEP-II LER synchrotron radiation and electron conditioning. –Test new structure concepts with very low effective SEY < 1: –grooved surfaces in PEP-II LER –clearing electrodes in PEP-II LER Electron Cloud and SEY R&D Program

6. Sep 26, 2006 Ongoing chamber projects at SLAC: Projects CLEARING ELECTRODES BENDPEP-II LER PR122007Design FINS TRIANG.BENDPEP-II LER PR122007Design TEST inLOCATIONReady for INSTALLATION Status SEY TESTSSTRAIGHTPEP-II LER PR12November 2006 Ready FINS RECTANG.STRAIGHTPEP-II LER PR12November 2006 Coating of extruded Al chambers Next chamber projects: M. Pivi, SLAC

7. Some past experience Laboratory measurements: conditioning: SEY~1. In vacuum de-conditioning brings up SEY ~ 1.3 KEKB tests: conditioning in situ. [Cross-benchmarking with simulations gives low SEY~1] SPS-CERN: conditioning in situ in the SPS. Minimum measured conditioned surface SEY~1.5. De-conditioning effect. Electron cloud effects decreased in time PSR-LANL: conditioning slow in time and de-conditioning. Still an issue. Measuring electron cloud since 1989! Da  ne: Luminosity reach is limited. (Aluminum SEY ~2.0 after conditioning) Bfactories: KEKB: smaller bunch spacing is limited by electron cloud. Still after years PEP-II: no problem up to 2.7A. Surface Conditioning (scrubbing)

8. Ongoing tests KEKB, CESRc, Dafne, PEP-II Next LHC will soon give answers. Note: LHC issues are heat load and single-bunch instability (p+ 450 GeV inj. energy). ILC DR issues are single-bunch instability and very small emittance preservation. Conditioning (scrubbing)

9. p.9 Design – Existing Ring Layout LER DIRECTION ELEVATION VIEW PLAN VIEW B1 AISLE SIDE REMOVE DRIFT HERE D. Arnett, SLAC ARC STRAIGHT

10. Coated sample exposed to SR in contact to chamber through RF seal PEP-II LER side RF seal location RF seal provide both RF sealing and thermal contact (Synch radiation load = 1W/cm at 4.7A) SEY TESTS TiN and NEG Expose samples to PEP-II LER synchrotron radiation and electron conditioning. Then, measure SEY in laboratory. Sample transferring under vacuum.

11. Sep 26, 2006 Sample position Stripe of SR Port with holes for electron cloud collector

12. Chamber with valves ion pump valve for rough pump valves PEP-II side 0 o position 45 o position

15. SEY test chamber (B. McKee chamber) Status: Completed fabrication of tunnel protections and chamber supports Completed assembly of transferring systems Completed samples TiN coating All parts Ready for installation Local controls hardware ready for assembly (by T. Porter) Test 1: Thermal dissipation tests: done Test 2: Transferring samples to-from lab. setup done Test 3: Solenoid ON/OFF in PR12 cell 9-10 done

17. p.17 Design- Fin Extrusions FIN TIPS= I.D. OF CHAM FAN HITS HERE FIRST LIGHT PASSES THRU SLOTS BETW FINS BECAUSE FAN IS “THICKER” THAN FIN FAN EVENTUALLY HITS “BOTTOM” OF SLOT FOR FULL SR STRIKE VIEW IS ROTATED 90 CCW FROM ACTUAL FAN ORIENTATION

18. p.18 Design- Fin Chamber m Chambers are constructed of Al extrusions machined to length with end preps for masks & flanges. m Al extrusions were chosen for their economy and ease of manufacture  Bonus - cooling is integral to the cross section, not welded to the outside m Flanges are bi-metal Atlas flanges that are welded directly to chamber  Insufficient space between the chamber and the flange knife edge for a bi-metal transition m Bottom sides of chambers are perforated at the ports m Inside surfaces are TiN coated  Reduce thermal outgassing & PSD  Reduce secondary electron yield? m Fin chamber weight ~ 32 lbs

19. p.19 Design- Port Detail m 4” port shown here, 500 holes, 25 x 20, holes 1.6 mm m 1.5” port hole pattern is 50 holes, 10x5, holes 1.6 mm

20. EXTRUSIONS Fin and flat chambers with cooling tubes, extrusion completed

21. Simulations rectangular groove profile. Reference SEY on a flat copper surface is ~1.7. w a h grooves parameters Simulation Rectangular Grooves By=0 case laboratory measurements of rectangular fin sample h=0.18” =0.089” a=0.089” w=0.022” Actual design chamber fins dimensions:

22. Rectangular Grooves to Reduce SEY USE IN STRAIGHT Without B field Rectangular grooves can reduce the SEY without generating geometric wakefields. USE IN BEND, WIGG, QUAD With B field Macro fins (mm scale) Micro fins (  m scale)

23. Simulations: Secondary electron yield = 0.8 Extrusion challenge Electron cloud diagnostic port per chamber in the center. Chamber Large fins

24. Sep 26, 2006 Ongoing chamber projects at SLAC: Projects CLEARING ELECTRODES BENDPEP-II LER PR122007Design FINS TRIANG.BENDPEP-II LER PR122007Design 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: M. Pivi, SLAC

25. Remedies simulation summary (see also L. Wang/M. Pivi talk Vancouver) L. Wang CLOUD_LAND code P. Raimondi, M. Pivi POSINST code 0 Voltage100 Voltage Bunch spacing = 6ns !Bunch spacing = 1.5ns !!

26. 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. Preliminary longitudinal impedance measurements at LBNL loss factor k=5e9 V/C. Optimized design should be tested in beam line with similar beam parameters  R&D at PEP-II, Cornell, KEK. LHC electrode design

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

28. Laboratory tests Copper Strips  Copper Foil Strips 1mil 5mil 20mil Used Coated with Kapton  3M Tape #5413  2.7mil thickness Brett Kuekan, Anatoly Krasnykh, M. Pivi SLAC Sep 2006

29. Preliminary reflection test HP 4 Channel reflectometer Brett Kuekan, Anatoly Krasnykh, M. Pivi SLAC Sep 2006 Measured loss factor

30. Longitudinal impedance bench measurements LBNL Experimental setup - coaxial wire method Initial results: peaks spacing is ~379 MHz i.e. a wavelength equal to twice the length of the test electrode ( /2 resonance). Our test pipe cutoff is around 3 GHz. Walling log formula for distributed impedances 378.75 MHz Loss factor (back of the envelope estimate) (Ohm) S. De Santis LBNL, M. Pivi SLAC Sep 2006

31. Expected power load onto electrode kloss [V/C]Bs [s]I [A]P [W] PEP-II3.4e94.2e-93.0125 ILCDR1.6e106.2e-90.524 Beam impedance related to impedance of transmission line Beam impedance Power onto electrode Where longitudinal gap between wall and electrode gap=0.003 and PEP-II  t  =40ps, rchamb=0.045m. ILC DR  t  =20ps, rchamb=0.022m. Brett Kuekan, Anatoly Krasnykh, M. Pivi SLAC Sep 2006

32. Option 1: four magnets chicane Layout PEP-II installation, PR12 LER e+e+ INSERTION BENDS 2kG Chamber layout PEP-II 1200mm Terminations load

33. Option 2: two magnets chicane (XCOR actual BMAX= 0.0875)

35. Triangular grooved surface in wiggler Effective SEY of an isosceles triangular surface with rounded tip.  max=1.74,  max=330eV, B0=0.2Tesla, Rtip=0.2mm, W=4.52mm. Effective SEY from an isosceles triangular surface in a dipole magnetic field.  max=1.74,  max=330eV, B0=1.6Tesla and W=1.89mm To reduce the impedance The effective SEY of triangular grooved surface has very weak dependence on the size W and magnetic field. (slac-pub-12001) Experiment in PEPII Dipole & CESR Wiggler L. Wang, SLAC

36. Fin structures in magnetic field 1) Proposed laboratory measurements 2) Chamber for installation in a dedicated bend in beam line at the same location as clearing electrode chamber

37. PROPOSED LABORATORY MEASUREMENTS: SEY OF GROOVE IN BEND e- beam triangular groove SLC FF 0.2 T

38. Rectangular fins: t = fin thickness p = fin pitch Resistive wall impedance increases by 47% for PEP-II fin-chamber design. K.Bane and G. Stupakov 19-23 July 2006

39. “Milestones” Date Project 1. Fabrication of the prototype rectangular chambers….............Done Installation in PEP-II LER ………………………………………Nov 2006 Project 2. Fabrication of SEY test chamber……………………………….Done Installation in PEP-II LER……………….…………………..….Nov 2006 Project 3: Fabrication of clearing electrode chamber…………………….Mar 2007 Complementary to Project 3: End Station A (SLAC) tests…...Mar 2007 Installation in PEP-II LER …………………………………….....Summer 2007 Project 4: Fabrication of triangular grooved chamber………………….…May 2007 Installation in PEP-II LER……………………..……………....…Summer 2007 Complementary to Project 4: meas. SEY in dipole….………..May 2007 LANL: measure electron trapping in quadrupole field PSR …………......Ongoing Frascati: installation of electron cloud diagnostic in Dafne ring……....…Summer 06 Cornell: measurements of electron cloud in wigglers………………...…..2008 Experimental R&D

40. Collective effects: Electron cloud simulation plans for FY07 Simulations on build-up for ILC DR, quadrupole and wigglers in progress Simulations on possible remedies to optimize design: clearing electr., RF, grooves in progress Maintain simulations codes POSINST, CLOUDLAND, and benchmarking ILC DR simulations with other codes ECLOUD, PEI, in progress Benchmarking simulations with ongoing experiments in PSR quadrupole in progress Simulations on fill pattern to reduce the electron cloud build-up in ILC DR Jan 2007 Benchmarking simulations with experiments in PEP-II Jan 2007 Benchmarking simulations with experiments in LHC Nov 2007 Developing “CMAD” self-consistent simulation code including e-cloud build-up and beam instabilities. Allow: tracking the beam in a MAD real lattice, interaction with cloud at each element of the ring, single- and coupled-bunch instability studies, threshold for SEY, dynamic aperture studies and frequency map analysis, tune shift. Status 85% done Feb 2007 Self-consistent simulation code: simulations for ILC and LHC (LARP collabor.) Mar 2007 Self-consistent simulation code: benchmarking with other single-bunch instability codes (HEAD-TAIL/PEHTS,ORBIT/QUICKPIC/WARP..) Apr 2007 Self-consistent simulation code: benchmarking with existing machines and LHC Nov 2007 ----- M. Pivi, SLAC 26 Sep 2006 -----

41. Resource loaded work plan for the design of the ILC damping rings in FY 2007: 1. Electron cloud simulation: 1.Design clearing electrode to install in LER of PEP-II 1.Simulation to optimize the design of clearing electrode 2.Estimate impedance and heating of the electrode 3.Classical instabilities 2.Design of micro-grooved chamber for bending magnet 1.Simulation to optimize the design of grooved surface 2.Estimate impedance 3.Classical instabilities 3.Study the electron cloud inside wigglers 4.Benchmark simulation existing codes 5.Develop a self-consistent codes for the electron cloud generation and instabilities

42. Resource loaded work plan for the design of the ILC damping rings in FY 2007: 1.Electron cloud simulation: (MP) 1.Design clearing electrode to install in LER of PEP-II 1.Simulation to optimize the design of clearing electrode(LW) 2.Estimate impedance and heating of the electrode(CN) 3.Classical instabilities(SH) 2.Design of micro-grooved chamber for bending magnet 1.Simulation to optimize the design of grooved surface(LW) 2.Estimate impedance(GS) 3.Classical instabilities(SH) 3.Study the electron cloud inside wigglers(LW) 4.Benchmark simulation existing codes(MP) 5.Develop a self-consistent codes for the electron cloud generation and instabilities (MP)

43. Collaborations: ILC  PEP-II, LBNL, Cornell, CERN, LANL. Collaborators: T. Raubenheimer, M. Pivi, J. Seeman. People involved: D. Arnett, D. Blankenship, B. Bigornia, N. Kurita, M. Pivi, M. Morrison, G. Stupakov, K. Bane, B. McKee, R. Kirby, G. Collet, K. Jobe, T. Smith, M. Ross, L. Wang, postdoc LC. SEY test chamber: chamber baked, thermal and transferring sample tests, assembling transferring systems Fins chambers: chamber extrusion manufacturing, ordered StSt/Al transition flanges, need manufacturing masks and e- detectors Clearing electrodes chambers: decision on chicane layout, need detaileddrawings. Triangular fins in bend: laboratory measurements, need detailed drawings R&D Status Summary

45. JULY 28, 2006 THERMAL DISSIPATION TESTS SAMPLE REACHED 58ºC AT 2.3 W, FOR LER CURRENT = 2.7A SAMPLE REACHED 84ºC AT 4.0 W, FOR LER CURRENT = 4.7A G. Collet, M. Pivi, R. Kirby SLAC - July 2006

46. Thanks ! To the contributors to this presentation M. Palmer (Cornell), S. De Santis (LBNL) F. Willeke (DESY), K. Suetsugu (KEK), K. Bane, P. Raimondi, L. Wang (SLAC), F. Zimmermann (CERN) and to DR collaborators D. Arnett, G. Collet, R. Kirby, N. Kurita, B. Mckee, M. Morrison, P. Raimondi, T. Raubenheimer, J. Seeman, L. Wang, G. Stupakov (SLAC), D. Rubin, D. Rice, L. Schachter, J. Codner, E. Tanke, J. Crittenden (Cornell), J. Gao (HIPEP), A. Markovic et al. (Rostock Univ.), M. Zisman, S. De Santis, C. Celata, M. Furman, J.L. Vay (LBNL), K. Ohmi, Y. Suetsugu (KEK), F. Willeke, R. Wanzenberg (DESY), E. Benedetto, F. Zimmermann, G. Rumolo, J.M. Jimenez, J-P. Delahaye (CERN), A. Wolski (Cockroft Uniiv.), B. Macek (LANL), C. Vaccarezza, S. Guiducci, R. Cimino (Frascati), et many other colleagues… Sep 26-28, 2006