1. ILC Damping Ring Collective Instability update: Electron Cloud Mauro Pivi SLAC ILC Vancouver Meeting July 19-22, 2006

2. History back to Nov 2005, DR recommendation What is changed by simulations, since then: - increased confidence that 2 x 6 km is safely below instability threshold - increased confidence on remedies, 1 DR may be feasible DR possible scenarios and risks: 2 DR vs 1 DR. Layout

3. Damping ring recommendation Simulated single bunch instability (SBI) thresholds and electron cloud build-up densities for peak secondary electron yield SEY=1.2 and 1.4. All TESLA wiggler aperture. PEHTS and POSINST codes benchmarked with ECLOUD, CLOUD_LAND, HEADTAIL. A large bunch spacing is desirable to limit the build-up of the electron cloud Task Force 6. K. Ohmi, M. Pivi, F. Zimmermann, Nov 2005.

4. Recent results for low Q (N=1x10 10 ) K.Ohmi (KEK) Ecloud: Threshold of electron cloud, 1.4x10 11 m -3. Ion: Feedback system can suppress for 650 MHz (3ns spacing), number of bunch in a train 45, and gap between trains 45ns..

5. Recent results: wiggler aperture increase 2 x 6km DR: Beneficial effect of increasing the wiggler chamber aperture. Margin of safety below the single-bunch instability (SBI) threshold.

6. Motivations for electron cloud studies and R&D For ILC Damping Ring: –If the Secondary electron yield (SEY) can be reduced in magnets, a smaller positron (6 km) ring can be feasible –promising cures in magnet regions as thin micro-fins and clearing electrodes need further R&D and full demonstration in accelerators For Super B factory: –Higher currents shorter bunch spacing For KEKb: –KEKb Annual Report 2005: "The electron cloud effect still remains the major obstacle to a shorter bunch spacing, even with the solenoid windings “ [1]. For LHC [1] http://www-kekb.kek.jp:16080/pukiwiki/index.php?Documentshttp://www-kekb.kek.jp:16080/pukiwiki/index.php?Documents

7. Extensive program worldwide incl. KEK, UK, Frascati, IHEP DR component optimization: wigglers, fast kickers; (Cornell) studies of the use of CESR as a DR test facility (in 2008) Damping Ring Design and Optimization (ANL) Lattice design and optimization; studies of ion instability in the APS ring; design of a hybrid wiggler E-cloud, SEY, FII simulations, experiments in PEP-II, KEKB, CESRc and Dafne rings (SLAC, KEK, CERN, Cornell, Frascati) ATF damping ring experiments (SLAC, LBNL, Cornell) Lattice designs for damping rings and injection/extraction lines; characterization of collective effects; stripline kickers for single- bunch extraction at KEK-ATF (LBNL) Damping ring R&D

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

9. 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

10. Very low SEY can be achieved. Triangular fin (grooves) SEY << 1 in magnets (see L. Wang talk) Rectangular groove SEY < 1 in magnets and field free. Fin-chamber (challenging) extrusion completed: four 2 meter long chambers will be installed in PEP-II at SLAC in fall 2006. Resistive wall impedance enhanced by 47% (K. Bane, G. Stupakov). Fin chambers PEP-II fin-chamber

11. ScenarioCollective instability Pro’sCon’sRisksR&D 1 DRe- cloud above SBI threshold 50% cost reduction, Reliability Need a cure for electron cloud in magnets Novel cures for electron cloud are technically not feasible Increase electron cloud R&D » 2 DRe- cloud below SBI threshold e- cloud SBI free, Upgradeability, Flexibility CostsNoneLater, after R&D, possibly decrease to 1 DR Possible ILC positron DR scenarios Risks: In the case of 1 DR: novel cures for electron cloud could not be technically feasible due to i) conditioning is not sufficient, ii) grooves or clearing electrodes generate HOM, large resistive wall impedance, large transverse impedance, and RF heating. In the case of 2 DRs: risks are low provided that e- cloud simulation predictions are giving good estimates. SBI = single bunch instability M. Pivi, ILC Meeting Vancouver 19-23 July 2006

12. The 2 x 6km ring is safely below single-bunch instability threshold and can accommodate rather large secondary electron yield values. In a single 6km ring, the electron cloud develops near threshold. High confidence given now by simulations on possible cures, including grooves and clearing electrodes. Need a full technical feasibility demonstration. Scenario 1: Decrease to 1 DR and increase R&D effort. (Sugg: by design 2nd ring built-in; be ready to install a 2nd ring. Not making it impossible). Scenario 2: Maintain 2 DR. Later, depending on R&D results, decrease to 1 DR. Scenarios summary

13. At the KEKB Positron Ring Test chambers (Cu, TiN-coated and NEG-coated) were installed in the KEKB positron ring. 3.5 GeV positron, stored beam current ~1.7 A. Number of electrons near the beam orbit was measured using a special electron monitor. SR of 1x10 16 photons/s/m/mA was irradiated at side wall. Incident angle ~8 mrad. Electron monitor Y.Suetsugu et al. KEK 2005.12.06

14. At the KEKB Positron Ring Y.Suetsugu et al. KEK 2006.07.06

15. Positron Measurements Positrons @ 5.3 GeV Single train of 45 bunches with 14 ns spacing –NOTE: at highest bunch currents, filling of bunches > #20 no longer uniform Plots –Top: Bunch Tune (kHz) vs Bunch –Bottom: BPM ADC level vs Bunch (note missing bunches at high bunch currents)

16. The use of the HERA Electron Ring in Conjunction with ILC Damping Rings Damping Ring Collaboration Meeting May9, 2006 F. Willeke, DESY Long term perspective Short term goals DR design examples Schedule Long term perspective Short term goals DR design examples Schedule

17. Possible Not-too-Far-Term DR Studies in HERA Storage of 250mA of positron with a bunch-spacing of 6-16 ns, study of electron-cloud issues, testing of remedies Demonstration of 1pm vertical emittance Demonstration of effective bba procedures Polarization test measurements De-install n.c. 500MHz cavities, RF feedbacks, 250MHz bandwidth MB damper improved HOM couplers at SCC Improved BPM electronics Additional BPMs Additional BBA circuitry Low  Measurement equipment ISSUE To be discussed and closely co-ordinated with GDE and DR collaboration! Additional Equipment Needed F. Willeke, DESY Damping Ring Collaboration Meeting May 9, 2006

18. 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, K. Bane, 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, J.M. Jimenez, J-P. Delahaye (CERN), A. Wolski (Cockroft Uniiv.), B. Macek (LANL), C. Vaccarezza, S. Guiducci, R. Cimino (Frascati), … July 19-22, 2006

19. 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, M. Pivi July 2006

20. 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