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Intra-Beam Scattering and Electron Cloud for the Damping Rings

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)

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Intra-Beam Scattering and Electron Cloud for the Damping Rings

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  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. Intra-Beam Scattering (IBS) Simulation Algorithm: CMAD IBS applied at each element of the Ring • CMAD parallel code: Collective effects & MAD • Lattice read from MADX files containing Twissfunctions 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 isincluded • Code physics: Electron Cloud + IBS + Radiation Damping & Quantum Excitation M. Pivi, T. Demma(SLAC, LAL), A. Chao (SLAC) May 9-11, 2012 Mauro Pivi, CERN, CLIC

  3. IBS - Zenkevich-BolshakovAlgorithm For two particles colliding with each other, the changes in momentum for particle 1 can be expressed as: with the equivalent polar angle effand 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 SIRE code uses similar implementation (A. VivoliFermilab, Y. Papaphilippou CERN) May 9-11, 2012 Mauro Pivi, CERN, CLIC collaboration

  4. IBS modeling: animation • http://www-user.slac.stanford.edu/gstewart/movies/particlesimulation_animation/

  5. IBS - SuperB LER Bane Piwinski IBS-Track IBS-Track C-MAD M. Pivi, T. Demma May 9-11, 2012 Mauro Pivi CERN, CLIC collaboration

  6. IBS - Swiss Light Source (SLS) -- 6×109 ppb -- 60 ×109 ppb -- 100 ×109 ppb Evolution of the emittances obtained by tracking with IBS for different bunch populations. Horizontallines: Piwinski (full) and Bane (dashed) models for the considered bunch populations. IBS_Track (T. Demma) See: Fanouria talk for SLS experimental results

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

  8. IBS - CLIC DR Ideal lattice • One turn evolutionof emittance in the CLIC DR.

  9. 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. 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 1st but not the 2nd. 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. Lattice with vertical quadrupole misalignments Vertical dispersions in DR lattice with misaligned quadrupolesdy=1um (Left) and dy=4.5um (Right) One turn matrix: large coupling terms for misalignment dy=4.5um

  12. Single particle tracking in lattice with misaligned quadrupoles Phase spaces of single particle, 1000 turns H V Z Quad misalignment: dy=1um dy=4.5um dy=1um and sextupole off

  13. 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 sigmazoscillates twice faster (Right) confirming Qs=7.18E-3 (period ~70 turns)

  14. 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. IBS evaluation: Long Term Plans • 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)

  16. Electron cloud in the Linear Colliders • 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. Global Design Effort

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

  18. Summary of Electron Cloud Mitigation Plan Mitigation Evaluation conducted at ILC DR Working Group Workshop meeting *Drift and Quadrupole chambers in arc and wiggler regions will incorporate antechambers • Preliminary CESRTA results and simulations suggest the possible presence of sub-threshold emittance growth • Further investigation required • May require reduction in acceptable cloud density a 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 M. Pivi, S. Guiducci, M. Palmer, J. Urakawa on behalf of the ILC DR Electron Cloud Working Group Global Design Effort

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

  22. Photon rates, by magnet type and regiondtc03 G. Dugan Cornell U. • Use Synrad3d a 3D simulation code that includes the ring lattice at input and chambers geometry (photon stops, antechambers, etc.)

  23. 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. Quadrupole in wiggler section • The calculated beampipe-averaged cloud densities does not reach equilibrium after 8 bunch trains. J. Crittenden, Cornell U.

  25. Quadrupole in wiggler section Electron cloud density (e/m3) Electron energies (eV) J. Crittenden, Cornell U.

  26. Sextupole in TME arc cell Electron cloud density (e/m3) Electron energies (eV) J. Crittenden, Cornell U.

  27. Clearing electrode in wiggler magnet Modeling of clearing electrode: round chamber is used Clearing Field (left) & potential (right) L. Wang, SLAC

  28. detail Electrodes with negative (above) or positive (below) potential -300V -600V 0v +600V +600V +400V +100V L. Wang, SLAC

  29. 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 4×1010 e/m3 (a factor 3 lower than the instability threshold evaluated in 2010 ...)

  30. 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. 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. Back up slides

  33. Bunch-slice parallel decomposition 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. M. Pivi (SLAC)

  34. Computational speed (CMAD) CMAD ideal e- cloud simulations IBS: Super-B, 300,000 macrop Room for code optimization IBS: Super-B, 100,000 macrop • IBS simulations: computing time per turn, Super-B lattice (1582 ring elements) 34 Mauro Pivi, CERN, CLIC collaboration

  35. 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. Previouswork: SIRE IBS Distribution study D: IBS A. Vivoli , Y. Papaphilippou

  37. Structured Evaluation of EC Mitigations Global Design Effort

  38. EC Mitigation Evaluation – 4 Criteria • Dedicated ILC DR Working Group Workshop Meeting to evaluate technologies and give recommendation on electron cloud mitigations 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 Global Design Effort

  39. Bends: Overall average EC density: all cases(QE=0.05) M. Furman, LBNL

  40. 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. Methodical Electron Cloud evaluation for CLIC DR: Major Research Goals. 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

  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 (BD = Beam Dynamics , TS = Technical Systems) Join us on the next DR meeting!

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