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Electron Cloud in Positron Rings and Intra-beam Scattering

Electron Cloud in Positron Rings and Intra-beam Scattering. Mauro Pivi, MedAustron - work made while at SLAC -

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Electron Cloud in Positron Rings and Intra-beam Scattering

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  1. Electron Cloud in Positron Rings and Intra-beam Scattering Mauro Pivi, MedAustron - work made while at SLAC - in collaboration with: T. Demma (Frascati & LAL), the ILC / CLIC and SuperBWorkingGroups, colleaguesat LBNL, CornellUniversity and SLAC.

  2. Intra-beam scattering • Intra-beam scattering (IBS) is associated with multiple small angle scattering events leading to emittance growth. • In most storage rings, typical radiation damping times are shorter than IBS growth times and IBS effect is not observed. • However, for high population and ultra-low emittance bunches, IBS may lead to emittance increase  IBS important for future colliders.

  3. IBS Formalisms, models and simulation tools • Piwinski, Bjorken and Mtingwa formalisms First formalisms ‘70/’80 for calculating IBS growth rates in storage rings based for Gaussian bunch distributions • K. Bane model High energy approximation for Gaussian beams • A. Chao model Novel analytical model, coupled differential eqs. valid for Gaussian beams • Semi-analitical model Using fit parameters from simulations iteratively, estimate emittance • Monte Carlo macroparticletracking code (T. Demma et al.) 6-D Monte Carlo, realistic studies for non-Gaussian beam distributions • ‘IBS-Track’ basedon Zenkevich-BolshakovAlgorithm • aims at exploring final equilibrium for non-Gaussian beams. Tails. • ex, ey and ezevolution in time Methods are in good agreement M. Boscolo, USR Workshop, Oct.30th 2012

  4. IBS – Monte Carlo code based on Zenkevich-BolshakovAlgorithm During the two particles small angle collision, the momentum change for 1 particle 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 M. Pivi, December 2015

  5. Intrabeam Scattering in SuperB LER Bane Piwinski IBS-Track Bane Piwinski IBS-Track T.Demma, INFN December 2011

  6. Emittance Evolution in SuperB LER • SuperB V12 LER Nb= 2x1010 - 12x1010 F=10 tx = 10-1 x 40 ms ty = 10-1x 40 ms ts = 10 -1x 20 ms T.Demma, INFN December 2011

  7. Simulations for SuperB Equilibriumhorizontal emittance vs bunch current Equilibrium longitudinal emittance vs bunch current The easy computable semi-analytical approach allows a quick scan of some key design parameters, such as the bunch population M. Boscolo, USR Workshop, Oct.30th 2012

  8. Intra-Beam Scattering (IBS) Simulation Algorithm: CMAD • The Monte Carlo IBS routine was imported in the CMAD (M.P.) code by Theo Demma. • CMAD parallel code: Collective effects &MAD • Accelerator lattice uploaded from MADXfiles • Bunch particles are 6D tracked along the ring. • The IBS scattering routine is called, at each element in the ring. IBS method: • All beam particles are grouped in cells. • Each 2 particles within a cell are coupled. • Momentum of 2 particles is changed due to scattering. • Radiation damping and excitation effects are evaluated at each turn. • Code physics: Electron Cloud + IBS + Radiation Damping & Quantum Excitation IBS applied at each element of the Ring M.Pivi, A.Chao, C.Rivetta, T.Demma, M.Boscolo, F. Antoniou, K.Li, Y.Papaphilippou, K.Sonnad, IPAC2012 T. Demma, M. Pivi May 9-11, 2012 Mauro Pivi, CERN, CLIC

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

  10. IBS - SuperB LER Bane Piwinski IBS-Track IBS-Track C-MAD T. Demma (INFN), M. Pivi (SLAC) December 2011

  11. EmittanceEvolution in SuperBLER M. Pivi (SLAC), T. Demma (INFN)

  12. IBS Distribution study: tails T. Demma (INFN), M. Pivi (SLAC)

  13. SIRE: IBS Distribution studyin CLIC DR: tails A. Vivoli (CERN)

  14. 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. • Comparison with experimental data at SLS: F. Antoniou et al. IPAC 2012 IBS_Track, T. Demma(INFN)

  15. SummaryIBS • Both tracking codes (INFN/CERN), that implement the Zenkevich-Bolshakovalgorithm, successfully benchmarked with conventional theories (i.e. K. Bane) and with the novel semi-analytical model. • Monte Carlo code was implemented in the parallelized CMAD code • Comparison between theoretical models and multi-particle algorithms, give good agreement for IBS dominated regimes. • IBS features that cannot be studied by analytical models such as the impact on the damping process and the generation of non- Gaussian tails can be investigated with multi-particles tracking codes. • Code benchmarked with SLS real data [F. Antoniou et al., IPAC2012], planned also with CESR-TA data. • Multi-particle codes are suited for studies of ultra-low emittance beams for future colliders.

  16. Electron cloud effect in proton and positron storage rings In a positron or proton storage ring, electrons are generated by a variety of processes, and can be accelerated by the beam to hit the vacuum chamber with sufficient energy to generate multiple “secondary” electrons (multipacting). Under certain conditions, the “electron cloud” density can reach high levels and can drive the beam unstable,increase the beam emittance, vacuum etc. decreasingthe collider performances. Electron cloud in the LHC 25 ns 25 ns

  17. The Secondary Electron Yield (SEY) on a surface: Key Parameter for Electron Multiplication Surface measurements at SLAC. F. Le Pimpecet al. • The secondary electron yield (SEY) is the number of electrons emitted per primary incident electron. It depends on: • the energy of the incident electron • Surface treatment and history For convenience the SEY maximum value is often quoted.

  18. Observations of Electron Cloud J. Flanagan et al. H. Fukuma et al. • KEK-B accelerator, Japan: the vertical bunch size increases along the train due to the build-up of the electron cloud density. • Electron cloud has been observed in several accelerators including: PEP-II, DAFNE, CESRTA, CERN SPS and at LHC.

  19. Electron cloud assessment Linear Colliders working group: Worldwide Laboratory Effort • Development of mitigation techniques: e- conditioning, surface coatings, clearing electrodes, grooves, solenoids • SEY measured on samples placed in accelerator environments: SLAC, CERN, KEK, CesrTA, Dafne • Instability simulations: to determine instability threshold • Build-up & evolution simulations: fed with measured SEY to evaluate level of electron cloud in the accelerator • Converge to recommendation for adoption of mitigations Global Design Effort

  20. Electron Cloud Effect Mitigations Electron “scrubbing” or “conditioning”: electrons impinging on the surface.  decrease of SEY linked to surface “graphitization” Secondary electron Yield (dmax) vs electron dose for different electron energies on LHC beam screen colaminated Cu. R. Cimino, T. Demma, M. Commisso, D. R. Grosso, V. Baglin, R. Flamminiand R. LarcipretePhys. Rev. Lett. 109, 064801 – 2012

  21. Electron Cloud Technical Mitigations Surface coating with low Secondary Electron Yield material Surface with grooves confine electrons e- Solenoid magnetic field modifies electron dynamics “Clearing” electrodes capture electrons in the time between bunches.

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

  23. Evaluation ofElectron Cloud Effect Used two categories of simulation codes: • The build-up codes: follow the evolution in time of the electron cloud interacting with a stable (fixed) beam. • Secondary electron yields as measured in accelerator environments and all technical mitigations are included in simulations. • The beam instability codes: assume already formed clouds with given density and track the beam particles. • used to define the cloud density that results in an instability threshold.

  24. Beam Instability Code: CMAD • CMAD(M. Pivi, Theo Demma, Kiran Sonnad, Claudio Rivetta): • The code simulates: • electron cloud instability. (Mauro P., Kiran S.) • Intra-beam scattering (Theo D.) • Feedback system to mitigate electron cloud instability (Claudio R.) • The accelerator model is uploaded via MAD-X. • The code tracks the beam for several turns and computes the electromagnetic interaction between particles in the beam and the electrons in the cloud. Parallelized code. CMAD has been used at a number of institutions including CesrTA Cornell University, Frascati Laboratory Italy and SLAC. M. Pivi, in the Proceedings PAC07 Conference THPAS066 (2007)

  25. Electron Cloud instability threshold 3.2 km ILC Damping Ring Cloud density (e/m3) 4.4e11 3.9e11 3.5e11 Instability simulations for the International Linear Collider Positron Damping Ring. Instability threshold ~2×1011 e/m3

  26. Build up simulations: Quadrupole in wiggler section Electron cloud density (e/m3) Electron energies (eV) J. Crittenden, Cornell U.

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

  28. Build-up simulations: Model of clearing electrode in wiggler magnets Modeling of clearing electrode: round chamber is used Clearing Field (left) & potential (right) L. Wang, SLAC

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

  30. 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.

  31. 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.

  32. Electron Cloud Mitigation Recommendation • Dedicated ILC DR Workshop at Cornell University, NY, USA 2010 on 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

  33. Structured Evaluation of EC Mitigations Global Design Effort

  34. 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 • 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 • 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

  35. Completing evaluation for ILC • With recommended mitigations the ring-average cloud density is 4×1010e/m3, well below the instability threshold of 2×1011e/m3. • ILC Technical Design Report 2012: implemented technical mitigations allowed reducing the size of the ILC damping rings to 3.2km (17km in 2004). • Mitigations adopted also at SuperKEKBand Daphne.

  36. e-Cloud @ DAFNE: Clearing ElectrodesD. Alesini, T. Demma et al. , in Proc. of IPAC 2010. Electric Field as computed by POISSON • Clearing electrodes are installed in the vacuum chambers of wigglers and dipoles of DAFNE positron ring. Electron cloudevolution with clearing electrodes (POSINST) 0 50 100 150 200 250 300 350 Time (ns) Theo Demma, INFN

  37. Clearing electrodes in DaFne Simulated evolution of the cloud density for different electrode voltage. Clearing electrodes ON/OFF: horizontal tune shift of 0.0065. D. Alesini, A. Drago, A. Gallo, S. Guiducci, C. Milardi, A. Stella, M. Zobov, S. De Santis, T. Demma, P. Raimondi, Phys Rev. Letters 110,124801 (2013)

  38. Effect of clearing electrodes on beam in DaFne Electrodes OFF Electrodes ON Beam dimension (um) at the Synchrotron light monitor turning all electrodes progressively off. Horizontal fractional tune as a function of bunch number along train of bunches. Growth rate of horizontal instability for different clearing electrode voltages. D. Alesini, A. Drago, A. Gallo, S. Guiducci, C. Milardi, A. Stella, M. Zobov, S. De Santis, T. Demma, P. Raimondi, IPAC 2012

  39. Electrod cloud mitigations in DaFne: clearing electrodes • Clearing electrodes installed in DaFne dipoles and wigglers • Experimental measurements have shown an impressive effectiveness of these devices in mitigating the e-cloud. • Electrodes ON indicate an evident reduction of the electron cloud density. • Electrodes allowed reducing the beam size, increase the instabilities growth rate, increase the beam current and luminosity.

  40. T. Demma: Preliminary results for SuperB =5x1011 =4x1011 =3x1011 Vertical emittance growth induced by e-cloud Input parameters (LNF conf.) for CMAD • The interaction between the beam and the cloud is evaluated at 40 Interaction Points around the SuperB HER (LNF option) for different values of the electoron cloud density. • The threshold density is determined by the density at which the growth starts:

  41. Buildup in Free Field Regions Snapshot of the electron (x,y) distribution 50G solenoids on Snapshot of the electron (x,y) distribution Solenoids reduce to 0 the e-cloud density at center of beam pipe Density at center of the beam pipe is larger then the average value.

  42. Buildup in the SuperB arcs: Quadrupoles LER Arc quadrupole vacuum chamber (CDR) dBy/dx=2.5T/m, =99% max=1.2 average center Cloud density average in chamber and near beam center Snapshot of the electron (x,y) distribution “just before” the passage of the last bunch

  43. Single Bunch Instability Threshold th= 1012 [e-/m3]

  44. T.Demma: Summary of electron cloud evaluation for SuperB • Single bunch instability simulations for SuperB HER V12 taking into account the effect of solenoids have been performed using CMAD. They indicate a threshold density of ~1012 e-/m3 (roughly 2 times previous estimates). • Build-up simulations Indicate SEY<1.2, eta < 0.05 as safe region for the single-bunch instability.. • But: • what is our confidence level in reaching these safe SEY values even including countermeasure such as antechambers, coatings, grooves, clearing electrodes…? • Do we have reliable estimates (from measurements) of parameters such as PEY, photon reflectivity…? December 2011

  45. Multi-particle code simulations T. Demma and M. Pivi, Collective effects in Super-B, IPAC 2010 C-MAD 0V +100V +1000V Electron cloud: emittance growth with cloud density in Super-B Electron cloud: clearing electrodes in Super-B IBS in Super-B; Theory compared with C-MAD and IBS-Track codes. Mauro Pivi • CODE DEVELOPMENT • SUMMARY • Evaluation of electron cloud build-up and instability in LHC, Super-B, ILC • Evaluation of IBS in ultra-low emittance rings: CLIC, Super-B • Validation of mitigations

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