1. Intra-Beam Scattering and Electron Cloud for the Damping Rings Mauro Pivi CERN/SLAC CLIC Collabortion Meeting CERN 9-11 May 2012 Thanks to: F. Antoniou, Y. Papaphilippou (CERN) T. Demma (LAL), A. Chao (SLAC) and the ILC electron cloud Working Group, i.p. M. Furman (LBNL), J. Crittenden (Cornell U.), L. Wang (SLAC).

2. 2 Intra-Beam Scattering (IBS) Simulation Algorithm: CMAD CMAD parallel code: Collective effects & MAD Lattice read from MADX files containing Twiss functions and transport matrices At each element in the ring, the IBS scattering routine is called. At each element: –Particles of the beam are grouped in cells. –Particles inside a cell are coupled –Momentum of particles is changed because of scattering. Particles are transported to the next element. Radiation damping and excitation effects are evaluated at each turn. Vertical dispersion is included Code physics: Electron Cloud + IBS + Radiation Damping & Quantum Excitation IBS applied at each element of the Ring M. Pivi, T. Demma (SLAC, LAL), A. Chao (SLAC) Mauro Pivi, CERN, CLIC May 9-11, 2012

3. 3 For two particles colliding with each other, the changes in momentum for particle 1 can be expressed as: with the equivalent polar angle  eff and the azimuthal angle  distributing uniformly in [0; 2  ], the invariant changes caused by the equivalent random process are the same as that of the IBS in the time interval  ts IBS - Zenkevich-Bolshakov Algorithm Mauro Pivi, CERN, CLIC collaboration SIRE code uses similar implementation (A. Vivoli Fermilab, Y. Papaphilippou CERN) May 9-11, 2012

4. 9-11 May, 2012 CLIC Collaboration Meeting IBS modeling: animation http://www- user.slac.stanford.edu/gstewart/movies/particl esimulation_animation/http://www- user.slac.stanford.edu/gstewart/movies/particl esimulation_animation/

5. 5 IBS - SuperB LER ParameterUnitValue EnergyGeV4.18 Bunch population10 6.5 Circumferencem1257 Emittances (H/V)nm/pm1.8/4.5 Bunch Lengthmm3.99 Momentum spread%0.0667 Damping times (H/V/L)ms40/40/20 N. of macroparticles-10 5 N. of grid cells-64x64x64 Bane Piwinski IBS-Track M. Pivi, T. Demma Mauro Pivi CERN, CLIC collaborationMay 9-11, 2012 IBS-Track C-MAD

6. 9-11 May, 2012 CLIC Collaboration Meeting IBS - Swiss Light Source (SLS) IBS_Track (T. Demma) See: Fanouria talk for SLS experimental results Evolution of the emittances obtained by tracking with IBS for different bunch populations. Horizontal lines: Piwinski (full) and Bane (dashed) models for the considered bunch populations. -- 6×10 9 ppb -- 60 ×10 9 ppb -- 100 ×10 9 ppb

7. 7 A. Vivoli, Y. Papaphilippou Previous work: SIRE Benchmarking (Gaussian Distribution) CLIC DR F. Antoniou, IPAC10

8. 9-11 May, 2012 CLIC Collaboration Meeting IBS - CLIC DR Ideal lattice One turn evolution of emittance in the CLIC DR. Energy (GeV) 2.86 emitx (m)5.554e-11 emity (m) 5.8193 e-13 Deltap 1.209209e-3 sigmaz (m) 0.001461

9. 9-11 May, 2012 CLIC Collaboration Meeting CLIC DR parameters optimization: IBS and bunch length Ideal lattice, no magnet misalignments or rotation One turn emittance evolution for different bunch lengths C:\Physics CLIC\2012 SIMULATIONS\CLIC_IBS_1GHz_ideal_lattice CMAD

10. 9-11 May, 2012 CLIC Collaboration Meeting Next step: include vertical Dispersion in CLIC DR In the vertical plane, IBS is much stronger in the presence of vertical dispersion. Then, it is crucial to include vertical dispersion in simulations to estimate the evolution of vertical emittance. We wish to generate a lattice with Vertical Dispersion but no Coupling to benchmark theoretical models that include the 1 st but not the 2 nd. Thus, in MADX we create quadrupole misalignments to generate vertical dispersion. In the CLIC DR (not in SLS), this generates also coupling due to Sextupoles. Then for now, turned off Sextupoles.

11. 9-11 May, 2012 CLIC Collaboration Meeting Lattice with vertical quadrupole misalignments Vertical dispersions in DR lattice with misaligned quadrupoles dy=1um (Left) and dy=4.5um (Right) One turn matrix: large coupling terms for misalignment dy=4.5um

12. 9-11 May, 2012 CLIC Collaboration Meeting Single particle tracking in lattice with misaligned quadrupoles Quad misalignment: dy=1um dy=4.5um dy=1um and sextupole off Phase spaces of single particle, 1000 turns H V Z

13. 9-11 May, 2012 CLIC Collaboration Meeting Review: RF parameters in CLIC DR lattice Issue: MADX computes Qs = 5.6782E-003 from RF cavity parameters By the One-Turn-Matrix, computed Qs = 7.183E-003 Tracking (below) shows a synchrotron tune Qs = 7.183E-003 Thus  reviewing the RF parameters and matching Beam tracking: Longitudinal centroid of the bunch (Left) oscillates with Qs=7.18E-3 (139 turns) and sigmaz oscillates twice faster (Right) confirming Qs=7.18E-3 (period ~70 turns)

14. 9-11 May, 2012 CLIC Collaboration Meeting IBS evaluation: Long Term Plans Code validation: benchmark recent experiments made at CesrTA and SLS with simulations Code predictions: long term beam evolution in CLIC Damping Rings –Fix RF system –Use ideal MAD lattice (no errors) –Include magnet vertical misalignments and vertical dispersion –Include magnet rotation and coupling also to closely benchmark experimental data (CesrTA, SLS) M. Pivi, F. Anotniou, Y. Papaphilippou (CERN)

15. 9-11 May, 2012 CLIC Collaboration Meeting Code use to optimize CLIC DRs: –Optimize ring parameters and IBS: beam energy, bunch length, optics Improve code speed: Merge wiggler elements in simulations Study the evolution of the bunch shape during IBS: generation of non-Gaussian tails IBS theoretical models: include betatron coupling M. Pivi, F. Anotniou, Y. Papaphilippou (CERN) IBS evaluation: Long Term Plans

16. 9-11 May, 2012 Electron cloud in the Linear Colliders Global Design Effort 16 SLAC is coordinating the ILC electron cloud Working Group (WG) WG milestones: evaluations and recommendations on electron cloud mitigations that lead to reduction of ILC DR circumference from 17km to 6km (2006) and from 6km to 3km (2010) 2012 goal is to evaluate electron cloud effect with mitigations implemented in each DR region, in preparation for the ILC Technical Design Report 2012.

17. Recommendation of Electron Cloud Mitigations 17 Clearing Electrodes KEKB Grooves w/TiN coating Clearing Electrode C ESR TA Grooves on Cu Stable Structures Reliable Feedthroughs Manufacturing Techniques & Quality amorphous-Carbon

18. 9-11 May, 2012 Preliminary C ESR TA results and simulations suggest the possible presence of sub-threshold emittance growth - Further investigation required - May require reduction in acceptable cloud density  reduction in safety margin An aggressive mitigation plan is required to obtain optimum performance from the 3.2km positron damping ring and to pursue the high current option *Drift and Quadrupole chambers in arc and wiggler regions will incorporate antechambers Summary of Electron Cloud Mitigation Plan Global Design Effort 18 Mitigation Evaluation conducted at ILC DR Working Group Workshop meeting M. Pivi, S. Guiducci, M. Palmer, J. Urakawa on behalf of the ILC DR Electron Cloud Working Group

19. Mitigations: Wiggler Chamber with Clearing Electrode Thermal spray tungsten electrode and Alumina insulator 0.2mm thick layers 20mm wide electrode in wiggler Antechamber full height is 20mm Joe Conway – Cornell U.

20. Mitigations: Dipole Chamber with Grooves 20 grooves (19 tips) 0.079in (2mm) deep with 0.003in tip radius 0.035in tip to tip spacing Top and bottom of chamber Joe Conway – Cornell U.

21. 9-11 May, 2012 Electron cloud assessment for 2012 TDR: Plans Photon generation and distribution PI: Cornell U. In BENDs with grooves PI: LBNL In WIGGLERS with clearing electrodes PI: SLAC In DRIFT, QUAD, SEXT with TiN coating PI: Cornell U. Input cloud density from build-up PI: SLAC Electron cloud Build-up Photon distribution Beam Instability

22. Photon rates, by magnet type and region dtc03 Use Synrad3d a 3D simulation code that includes the ring lattice at input and chambers geometry (photon stops, antechambers, etc.) G. Dugan Cornell U.

23. 9-11 May, 2012 CLIC Collaboration Meeting Electron Cloud in Drift Regions, with Solenoid field (40 G) Solenoid fields in drift regions are very effective at eliminating the central density J. Crittenden, Cornell U.

24. 9-11 May, 2012 CLIC Collaboration Meeting Quadrupole in wiggler section The calculated beampipe-averaged cloud densities does not reach equilibrium after 8 bunch trains. J. Crittenden, Cornell U.

25. 9-11 May, 2012 CLIC Collaboration Meeting Quadrupole in wiggler section Electron cloud density (e/m 3 ) Electron energies (eV) J. Crittenden, Cornell U.

26. 9-11 May, 2012 CLIC Collaboration Meeting Sextupole in TME arc cell Electron cloud density (e/m 3 ) Electron energies (eV) J. Crittenden, Cornell U.

27. 9-11 May, 2012 CLIC Collaboration Meeting Clearing electrode in wiggler magnet Modeling of clearing electrode: round chamber is used Clearing Field (left) & potential (right) L. Wang, SLAC

28. 9-11 May, 2012 CLIC Collaboration Meeting detail +600V 0v +600V +400V +100V -300V -600V L. Wang, SLAC Electrodes with negative (above) or positive (below) potential

29. 9-11 May, 2012 CLIC Collaboration Meeting Completing evaluation for ILC Next steps: 1) Simulations to include grooves in Bends 2) Beam instability simulations using electron cloud densities from build-up simulations. At this stage, with recommended mitigations, the ring-average cloud density is 4 × 10 10 e/m 3 (a factor 3 lower than the instability threshold evaluated in 2010...)

30. 9-11 May, 2012 CLIC Collaboration Meeting CLIC DR: Electron Cloud R&D program 2008 simulations: electron cloud strongly destabilize the beam and deposit excessive heat load in SC wigglers. 2008 studies are currently the latest results. Electron cloud effect is high priority issue for the CLIC DRs. In 2009, CLIC has been re-designed with several changes in the DR parameters: beam energy, circumference, all others Need for an up-to-date R&D program to: –systematically evaluate the electron cloud build-up and instabilities in the present DR configuration –properly select mitigation techniques to be implemented in each of the DR regions –overcome the beam instability and excessive heat loads

31. 9-11 May, 2012 CLIC Collaboration Meeting Summary Intra-Beam Scattering codes in agreement with theoretical models Estimations for Super-B and SLS, CesrTA Plans for methodical evaluation of IBS in CLIC Damping Rings Evaluation of electron cloud in ILC ongoing for Technical Design Report (2012) Need for re-evaluation of electron cloud in CLIC Damping Rings

32. 9-11 May, 2012 CLIC Collaboration Meeting Back up slides

33. 33 Computation in parallel - pipeline Each processor deals with the bunch-slice, then send information to the next in the pipeline. The last processor print out the beam information. At each turn, 1 processor gathers all particles and compute Radiation Damping and Quantum Excitation. Bunch-slice parallel decomposition M. Pivi (SLAC)

34. 9-11 May, 2012 Computational speed (CMAD) IBS simulations: computing time per turn, Super-B lattice (1582 ring elements) Mauro Pivi, CERN, CLIC collaboration 34 1 processor64 processors 100,000 macroparticle200 sec18.5 sec 300,000 macroparticle540 sec24.4 sec ideal e - cloud simulations IBS: Super-B, 100,000 macrop IBS: Super-B, 300,000 macrop Room for code optimization CMAD

35. 9-11 May, 2012 CLIC Collaboration Meeting Intra-Beam Scattering – CLIC DR Overview Previous work with SIRE simulation code Evaluation of IBS with CMAD during one turn in ideal lattice (no errors) to compare with theory Vertical dispersion and coupling Plans for IBS evaluation

36. 36 Previous work: SIRE IBS Distribution study D: IBS ParameterValue Eq.  x (m rad) 2.001e-10 Eq.  y (m rad) 2.064e-12 Eq.   1.992e-3 Eq.  z (m) 1.687e-3 Parameter    Confidence  p/p 3048.7<1e-15 X1441.7<1e-15 Y1466.9<1e-15 A. Vivoli, Y. Papaphilippou

37. Structured Evaluation of EC Mitigations Nov 3-4, 2011 CLIC coll. meeting Global Design Effort 37

38. EC Mitigation Evaluation – 4 Criteria Global Design Effort 38 Efficacy Photoelectric yield (PEY) Secondary emission yield (SEY) Ability to keep the vertical emittance growth below 10% Cost Design and manufacturing of mitigation Maintenance of mitigation –Ex: Replacement of clearing electrode PS Operational –Ex: Time incurred for replacement of damaged clearing electrode PS Risk Mitigation manufacturing challenges: –Ex: ≤1mm or less in small aperture VC –Ex: Clearing electrode in limited space or in presence of BPM buttons Technical uncertainty –Incomplete evidence of efficacy –Incomplete experimental studies Reliability –Durability of mitigation –Ex: Damage of clearing electrode feed- through Impact on Machine Performance Impact on vacuum performance –Ex: NEG pumping can have a positive effect –Ex: Vacuum outgassing Impact on machine impedance –Ex: Impedance of grooves and electrodes Impact on optics –Ex: x-y coupling due to solenoids Operational –Ex: NEG re-activation after saturation Nov 3-4, 2011 CLIC coll. meeting Dedicated ILC DR Working Group Workshop Meeting to evaluate technologies and give recommendation on electron cloud mitigations

39. M. Furman, p. 39ILCDR EC buildup: DTC03 vs. DSB3 4/19/12 Bends: Overall average EC density: all cases (QE=0.05) M. Furman, LBNL

40. 9-11 May, 2012 CLIC Collaboration Meeting Methodical Electron Cloud evaluation for CLIC DR: Major Research Goals. Phase I. Simulation R&D effort. Characterize the photon generation and details of the photoelectron distribution in the whole damping ring Characterize the electron cloud (EC) effect in field free regions, dipole, quadrupole, sextupole and wiggler regions Estimate effect of antechamber and photon stop designs on EC build-up Perform parameter space studies: vacuum chamber radii, base vacuum pressure, scan of the secondary electron yield and beam parameters, antechamber and photon stop design Estimate the single-bunch instability threshold by simulations and for a realistic CLIC damping ring lattice Investigate coupled-bunch instability by simulations: quantify growth rate and address feedback system Define the maximum acceptable secondary electron yield SEY level, above which the beam would be unstable

41. 9-11 May, 2012 CLIC Collaboration Meeting Phase II. R&D on mitigations and recommendation: Estimate beneficial effect of solenoid field in field free regions Investigate efficacy of technical mitigations on suppressing electron cloud build-up by simulations Experimental R&D effort on mitigations tailored to the CLIC DR : amorphous Carbon, NEG and TiN coating, clearing electrodes, grooves Evaluate impact on impedance for possible mitigations: all coating options, clearing electrodes, grooves and photon stops Give recommendation for technical mitigations for each machine region Give recommendation on the design and specifications of mitigations Methodical Electron Cloud evaluation for CLIC DR: Major Research Goals.

42. Change energy: scale H emittance (epsxnew=epsold*newgamma^2/gamma^2), energy spread deltapnew=deltapold*energynew/energyold, tau to be updated (not needed 1 turn); Optics scale the magnets …

43. CLIC DR meetings It is important to continuously and dynamically, i.e. critically, review our work Goal is to communicate during informal meetings about beam dynamics and technical issues and/or progress In the these meetings, you are encouraged to ask openly several questions to favour exchange of information and a deeper understanding of beam instabilities, collective effects and technical systems, as a group. M. Pivi, Y. Papaphilippou and F. Antoniou

44. CLIC DR meetings The format of the new meetings: Every month meet with all DR group including Technical Systems and Beam Dynamics Every 2 weeks meet with Beam Dynamics group M. Pivi, Y. Papaphilippou and F. Antoniou

45. CLIC DR Meetings Schedule DateMeeting Wednesday 23 rd MayBD Wednesday 6 th JuneTS and BD Tentative: Wednesday 13 th JuneBD Tentative: Wednesday 27 th JuneTS and BD (BD = Beam Dynamics, TS = Technical Systems) Join us on the next DR meeting!