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)

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

• 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, CLICMay 9-11, 2012

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

9-11 May, 2012 CLIC Collaboration Meeting

IBS modeling: animation

• http://www-user.slac.stanford.edu/gstewart/movies/particlesimulation_animation/

http://www-user.slac.stanford.edu/gstewart/movies/particlesimulation_animation/

http://www-user.slac.stanford.edu/gstewart/movies/particlesimulation_animation/

5

IBS - SuperB LER

Parameter Unit ValueEnergy GeV 4.18Bunch population 1010 6.5 Circumference m 1257 Emittances (H/V) nm/pm 1.8/4.5 Bunch Length mm 3.99 Momentum spread % 0.0667 Damping times (H/V/L) ms 40/40/20 N. of macroparticles - 105 N. of grid cells - 64x64x64

Bane PiwinskiIBS-Track

M. Pivi, T. DemmaMauro Pivi CERN, CLIC collaborationMay 9-11, 2012

IBS-Track C-MAD


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.

-- 6×109 ppb-- 60 ×109 ppb-- 100 ×109 ppb

7A. Vivoli, Y. Papaphilippou

Previous work: SIRE Benchmarking (Gaussian Distribution) CLIC DR

F. Antoniou, IPAC10


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


CLIC DR parameters optimization: IBS and bunch length

Ideal lattice, no magnet misalignments or rotation

One turn emittance evolution for different bunch lengths

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CMAD


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.


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


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


Review: RF parameters in CLIC DR latticeIssue:• 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)


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)


• 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

couplingM. Pivi, F. Anotniou, Y. Papaphilippou (CERN)

IBS evaluation: Long Term Plans

9-11 May, 2012 Global Design Effort

Electron cloud in the Linear Colliders

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.

Recommendation of Electron Cloud Mitigations

17

Clearing ElectrodesKEKB

Grooves w/TiN coating

Clearing ElectrodeCESRTA

Grooves on Cu

Stable Structures

Reliable Feedthroughs

Manufacturing Techniques& Quality

amorphous-Carbon

9-11 May, 2012

• 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

ILC Working Group Baseline Mitigation Recommendation

Drift* Dipole Wiggler Quadrupole*

Baseline Mitigation I TiN Coating

Grooves with

TiN coating

Clearing Electrodes TiN Coating

Baseline Mitigation II

Solenoid Windings Antechamber Antechamber

Alternate Mitigation

Carbon coating/ NEG

CoatingTiN Coating Grooves with TiN

CoatingClearing Electrodes

or Grooves*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

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.

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.

9-11 May, 2012

Electron cloud assessment for 2012 TDR: Plans

Photon generation and distributionPI: Cornell U.

In BENDs with groovesPI: LBNL

In WIGGLERS with clearing electrodesPI: SLAC

In DRIFT, QUAD, SEXT with TiN coatingPI: Cornell U.

Input cloud density from build-upPI: SLAC

Electron cloud Build-up

Photon distribution Beam Instability

Photon rates, by magnet type and regiondtc03

Use Synrad3d a 3D simulation code that includes the ring lattice at input and chambers geometry (photon stops, antechambers, etc.)

G. Dugan Cornell U.


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.


Quadrupole in wiggler section• The calculated beampipe-averaged cloud densities does not

reach equilibrium after 8 bunch trains.



Quadrupole in wiggler section

Electron cloud density (e/m3) Electron energies (eV)



Sextupole in TME arc cell

Electron cloud density (e/m3) Electron energies (eV)



Clearing electrode in wiggler magnet

Clearing Field Potential

X (mm)

Y (

mm

)

11.7272

23.4013

35.0755

46.7496

81.772

140.1426

210.1874

303.5804

373.6252

467.0182

-20 -10 0 10 20

-20

-15

-10

-5

0

5

10

15

Modeling of clearing electrode: round chamber is used

Clearing Field (left) & potential (right) L. Wang, SLAC


detail

+600V

0v

+600V+400V +100V

-300V -600V

L. Wang, SLAC

Electrodes with negative (above) or positive (below) potential


Completing evaluation for ILC

Next steps:1) Simulations to include grooves in Bends2) 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 ...)


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


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


Back up slides

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)

9-11 May, 2012

Computational speed (CMAD)

IBS simulations: computing time per turn, Super-B lattice (1582 ring elements)

Mauro Pivi, CERN, CLIC collaboration34

1 processor 64 processors

100,000 macroparticle 200 sec 18.5 sec

300,000 macroparticle 540 sec 24.4 sec

ideal

e- cloud simulations

IBS: Super-B, 100,000 macrop

IBS: Super-B, 300,000 macrop

Room for code optimization

CMAD


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

Previous work: SIRE IBS Distribution study D: IBS

Parameter Value

Eq. ex (m rad) 2.001e-10

Eq. ey (m rad) 2.064e-12

Eq. sd 1.992e-3

Eq. sz (m) 1.687e-3

Parameter c2999 Confidence

Dp/p 3048.7 <1e-15

X 1441.7 <1e-15

Y 1466.9 <1e-15

A. Vivoli , Y. Papaphilippou

Structured Evaluation of EC Mitigations

Nov 3-4, 2011 CLIC coll. meeting

Global Design Effort 37

Criteria for the evaluation of mitigations: Working Group rating

Efficacy of Mitigation

Costs RisksImpact on Machine

Rating 10 1 4 4

Normalized Weighting 0.53 0.05 0.21 0.21

Global Design Effort

EC Mitigation Evaluation – 4 Criteria

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 PSRisk

• 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

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


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


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.

• 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 …

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

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

CLIC DR Meetings Schedule

Date Meeting

Wednesday 23rd May BD

Wednesday 6th June TS and BD

Tentative: Wednesday 13th June BD

Tentative: Wednesday 27th June TS and BD

(BD = Beam Dynamics , TS = Technical Systems)

Join us on the next DR meeting!

Intra-Beam Scattering and Electron Cloud for the Damping Rings

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