1. ILC Damping rings G. Dugan PAC TDR review 12/13/12 Dec. 13, 2012 ILC Damping Rings 1

2. Outline Requirements Configuration, parameters, operating modes Lattice Beam dynamics issues –Emittance tuning and nonlinear effects –Electron cloud effect –Fast ion instability Technical systems –RF –Magnets and power supplies –Vacuum, instrumentation and feedback –Injection/extraction Conclusion ILC Damping Rings Dec. 13, 2012 2

3. Damping rings functional requirements Dec. 13, 2012 ILC Damping Rings 3 accept e - and e + beams with large transverse and longitudinal emittances from the sources and produce the low-emittance beams required for high-luminosity production; damp incoming beam jitter (transverse and longitudinal) and provide highly stable beams for downstream systems; delay bunches from the source to allow feed-forward systems to compensate for pulse-to-pulse variations in parameters such as the bunch charge.

4. Dec. 13, 2012 ILC Damping Rings 4 Ring Configuration Circumference: 3238 m, 2 x 710 m straights 5.6 μm-rad < γε x < 6.4μm-rad 5414-pole wigglers : length 2.1 m, B peak 2.2 T, period 30 cm =>24 ms >  x > 12 ms e + (baseline) e - (baseline) Phase trombone  ± 0.5 λ β Chicane  ± 4 mm pathlength 12 – 650 MHz RF cavities => σ l = 6 mm Harmonic number 7022 e + (future option)

5. Dec. 13, 2012 ILC Damping Rings 5 Operating modes and ring parameters Three ILC operating modes correspond to four DR configurations Two modes utilize a 5 Hz repetition rate: low power baseline (1312 bunches/ring); and high luminosity upgrade (2625 bunches). Third operating mode is at 10 Hz, with e- linac operated with alternating pulses: high energy for e+ production followed by low energy for collisions. Shorter damping times necessary to achieve the same extracted vertical emittance in half the nominal storage time.

6. Dec. 13, 2012 ILC Damping Rings 6 Ring lattice extraction arc phase trombone RF wigglers arc circumference chicane injection

7. Arc cells Dec. 13, 2012 ILC Damping Rings 7 Each cell contains : 1 - 3m dipole, θ = π/75 3 – quadrupoles 4 - sextupoles 3 - corrector magnets 1-horizontal steering 1-vertical steering 1- skew quad 2 beam position monitors 75-cells/arc BPM

8. Wiggler straight –2 wigglers/cell –30 cells –2.1 m wiggler –1.5T< B peak < 2.2T –54 @ 2.16T => τ x =13ms (10Hz) –54 @ 1.51T => τ x = 25ms (5Hz) –3 empty cells will accommodate 6 additional wigglers if required –H&V dipole corrector and BPM adjacent to each quad Damping Wigglers Dec. 13, 2012 ILC Damping Rings 8

9. RF straight Dec. 13, 2012 ILC Damping Rings 9 RF –2 cavities/cell –22.4 MV => 6mm bunch length @  x =13ms => for 12 cavities 1.9MV/cavity 272kW/coupler Lattice can accommodate 16 cavities if required Cavities offset so that waveguides of upper and lower rings are interleaved H&V corrector and BPM adjacent to each quadrupole

10. Emittance in 3 rd GLS, DR and colliders R. Bartolini Low Emittance Rings Workshop, Crete 3 rd October 2011 Dec. 13, 2012 ILC Damping Rings 10 Emittance tuning-1 CesrTA ATF Note that LS emittance results are for electron rings.

11. Emittance tuning-2 Dec. 13, 2012 ILC Damping Rings 11 Measure and correct orbit using all steerings Measure betatron phase advance (by resonant excitation) – and correct using quadrupoles Measure coupling (by resonant excitation) and correct with skew quads Measure orbit, coupling, and vertical dispersion and simultaneously correct with vertical steerings and skew quads ParameterRMS BPM – Differential resolution2 μm BPM – Absolute resolution100 μm BPM – Tilt10 mrad BPM button – Gain variation1% Quads + Sexts – Offset (H+V)50 μm Quads – Tilt100 μrad Dipole – Roll100 μrad Wiggler – Offset (V only)200 μm Wiggler - Roll200 μrad Design: 2 pm

12. Nonlinear effects Dec. 13, 2012 ILC Damping Rings 12 Magnet misalignments as on previous slide. Magnet multipole errors based on PEPII and SPEAR magnet measurements. Wiggler nonlinearities based on numerical wiggler field model, checked against Cesr wiggler field measurements. Dynamic aperture with specified magnet misalignments and field errors, and full Taylor map for wiggler nonlinearities Tune footprint Injected positron beam

13. Dec. 13, 2012 ILC Damping Rings 13 Electron Cloud Effect-outline Vacuum chamber design to minimize photon absorption in the chamber Vacuum chamber surface EC mitigation EC buildup simulations to estimate ringwide average cloud density Comparison with analytic estimate of instability threshold Comparison with numerical simulations of coherent and incoherent emittance growth using CMAD

14. DR Vacuum System Design Dec. 13, 2012ILC Damping Rings14 Antechamber with slanted interior end to reduce photon backscattering Fully-absorbing photon stops DR vacuum chamber has been designed with the help of a new photon tracking code (Synrad3D) developed for CesrTA The code allows accurate determination of antechamber features to limit the number of photons absorbed within the vacuum chamber. It also provides an accurate estimate of the sources of the photoelectrons which seed development of the electron cloud. Note that the vacuum chambers are shown rotated by 90 o relative to their installed orientation.

15. Vacuum chamber surface treatment for SEY suppression Mitigation Evaluation conducted at satellite meeting of ECLOUD`10 (October 13, 2010, Cornell University) Dec. 13, 2012ILC Damping Rings15 SuperKEKB Dipole Chamber Extrusion DR Wiggler chamber concept with thermal spray clearing electrode – 1 VC for each wiggler pair. Y. Suetsugu Conway/Li SEY, TiN, from CesrTA RFA current in wiggler, from CesrTA

16. 16ILC Damping Rings EC Suppression by Wiggler Electrode: Crittenden Wang Electron cloud density from buildup simulations Trapping in quadrupoles Cloud density is average over 20 sigma around the beam, just before the pinch, in units of 10 11 /m 3. Length is in meters. Dipoles have no grooves. Based on photon rates from Synrad3D; Peak SEY = 0.94 (TiN) Solenoids in drifts produce 100% suppression of cloud near the beam Dec. 13, 2012

17. ILC Damping Rings 17 Beam energy (GeV)245 CesrTA observed instability threshold (x10 11 /m 3 )820 CesrTA threshold density, analytic estimate (x10 11 /m 3 )1327 ILCDR threshold density, analytic estimate (x10 11 /m 3 )2.3 ILCDR threshold density, analytic estimate, scaled down based on CesrTA observations (x10 11 /m 3 ) ~1.5 ILCDR estimated ringwide average density, from simulation (x10 11 /m 3 )~0.35 Comparison with instability thresholds Analytic estimate (in coasting beam approximation) for the electron cloud density at threshold (Jin,Ohmi): [Jin, Ohmi]: H. Jin et al., “ Electron Cloud Effects in Cornell Electron Storage Ring Test Accelerator and International Linear Collider Damping Ring,” Jpn. J. Appl. Phys. 50, 026401 (Feb. 2011). ILCDR ringwide density/threshold density ~ 0.35/1.5 ~ 0.23

18. CMAD simulations of EC-induced emittance growth Dec. 13, 2012 ILC Damping Rings 18 There is a clear threshold to exponential growth between (3 – 5) x10 11 /m 3 cloud density Real DR lattice, 0.35x10 11 /m 3 cloud density Incoherent emittance growth at 0.35x10 11 /m 3 is about.001 in 300 turns Incoherent emittance growth at 0.35x10 11 /m 3 is about.0016 in 300 turns The store time is about 18,000 turns The emittance growth during the store time should be about 10%. Radiation damping is not included. Damping time is about 2,000 turns. Smooth focusing lattice

19. Fast Ion Instability in Electron Damping Ring Dec. 13, 2012 ILC Damping Rings 19 Simulation Codes confirmed by experimental results at ATF-DR, CesrTA, SPEAR3 and low emittance SR Rings Control of this instability requires Low base vacuum pressure ~ 10 -7 Pa Gaps (43 RF buckets) between mini-trains Bunch-by-bunch feedback system with a 20 turn (~0.2 ms) damping time No gap 43 RF bucket gap

20. Technical systems: RF Dec. 13, 2012 ILC Damping Rings 20 12 650 MHz SCRF cavities, operating CW at 4.5K Gradient 6-8 MV/m 6 klystrons, peak power 0.7 MW CW 3 Operating modes: Baseline: 2 MW RF power, 10 cavities, 14 MV RF 10 Hz: 3.8 MW RF power, 12 cavities, 22 MV RF Upgrade: 3.8 MW RF power, 12 cavities, 14 MV RF

21. Technical systems: Magnets and Power supplies Dec. 13, 2012 ILC Damping Rings 21 Conventional magnets Power supply system design based on “bus” powering of DC- to-DC converters for individual magnet supplies. Superconducting magnets 54 superferric wigglers, operating at 4.5K Design based on Cesr-c experience Shorter period, higher field than RDR spec.

22. Technical systems: vacuum and instrumentation Dec. 13, 2012 ILC Damping Rings 22 Antechambers and electron cloud mitigation as presented in slides 13, 14. Base pressure 10 -7 Pa from NEG strips in the dipole and wiggler antechambers. Localized ion pumps (~5 m) and TiSP pumps. Sufficient pumping speed to handle conditioning requirements. Sliding joints cover bellows to control impedance Vacuum system: BPMs with specifications given in slide 10. Tune trackers Visible and/or X-ray SR light monitors Current monitors Beam-loss monitors Fast feedback systems to control coupled-bunch instabilities Bunch-by-bunch, all 3 planes Bandwidth > 650 MHz Damping time ~0.2 ms 1 kW power Instrumentation system:

23. Technical systems: Injection/Extraction Dec. 13, 2012 ILC Damping Rings 23 Tests at ATF with FID pulser have demonstrated required rise/fall times, jitter tolerance Kicker impedance issues still to be resolved Individual bunch injection/extraction (in the horizontal plane) requires very fast, very stable kickers Extraction kicker pulse rate 1.8 MHz (3 MHz for lumi upgrade) For 6 ns bunch spacing, require rise/fall time ~ 6 ns (3 ns for lumi upgrade) 42 strip-line 50  kicker modules, 30 cm long, 30 mm gap Total kick angle ~0.6 mrad (10 kV pulse on each electrode) for extracted beam Kicker jitter tolerance (kick amplitude stability) < 5 x 10 -4 Good field quality is required for the pulsed magnets (kicker, septum) in the extraction channel to preserve the ring emittance after extraction. Remainder of injection/extraction system is conventional and straightforward.

24. Conclusion Dec. 13, 2012 ILC Damping Rings 24 The TDR design for the ILC Damping rings has been reviewed. The functional requirements, the ring configuration, and the principal parameters and operating modes have been described. The lattice design has been outlined. The leading beam dynamics issues impacting ring performance have been discussed: –Emittance tuning and nonlinear effects –Electron cloud effect –Fast ion instability The key elements of the principal technical systems have been described: –RF –Magnets and power supplies –Vacuum, instrumentation and feedback –Injection/extraction