Mauro Pivi CERNSLAC CLIC Collabortion Meeting CERN 911 May 2012 Thanks to F Antoniou Y Papaphilippou CERN T Demma LAL A Chao SLAC ID: 798577
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Slide1
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).
Slide2Intra-Beam Scattering (IBS) Simulation Algorithm: CMAD
CMAD parallel code:
C
ollective effects &
MADLattice read from MADX files containing Twiss functions and transport matricesAt 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 coupledMomentum 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
Slide3For 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 tsIBS - Zenkevich-Bolshakov AlgorithmMauro Pivi, CERN, CLIC collaborationSIRE code uses similar implementation (A. Vivoli Fermilab, Y. Papaphilippou CERN)May 9-11, 2012
Slide4IBS modeling: animation
http://www-user.slac.stanford.edu/gstewart/movies/particlesimulation_animation/
IBS - SuperB LER
Parameter
Unit
Value
EnergyGeV4.18Bunch population10106.5
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
-
10
5
N. of grid cells-64x64x64
Bane PiwinskiIBS-Track
M. Pivi, T. Demma
Mauro Pivi CERN, CLIC collaboration
May 9-11, 2012
IBS-Track
C-MAD
Slide6IBS - Swiss Light Source (SLS)
IBS_Track
(T.
Demma
) See: Fanouria talk for SLS experimental resultsEvolution 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
Slide7A.
Vivoli
, Y.
Papaphilippou
Previous work: SIRE Benchmarking (Gaussian Distribution) CLIC DRF. Antoniou, IPAC10
Slide8IBS - CLIC DR
Ideal lattice
One turn evolution
of emittance in the CLIC DR. Energy (GeV)2.86emitx (m)5.554e-11emity (m)
5.8193 e-13Deltap
1.209209e-3sigmaz (m)
0.001461
Slide9CLIC DR parameters
optimization
: IBS and bunch length
Ideal lattice, no magnet misalignments or rotation
One turn emittance evolution for different bunch lengthsC:\Physics CLIC\2012 SIMULATIONS\CLIC_IBS_1GHz_ideal_latticeCMAD
Slide10Next 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 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.
Slide11Lattice 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
Slide12Single particle tracking in lattice with misaligned quadrupoles
Quad misalignment:
dy
=1um
dy=4.5um dy=1um and sextupole offPhase spaces of single particle, 1000 turnsHVZ
Slide13Review: 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-003Tracking (below) shows a synchrotron tune Qs = 7.183E-003Thus reviewing the RF parameters and matchingBeam 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)
Slide14IBS 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 RingsFix RF systemUse ideal MAD lattice (no errors)Include magnet vertical misalignments and vertical dispersionInclude magnet rotation and coupling also to closely benchmark experimental data (CesrTA, SLS)M. Pivi, F. Anotniou, Y. Papaphilippou (CERN)
Slide15Code use to optimize CLIC DRs:Optimize ring parameters and IBS: beam energy, bunch length, optics
Improve code speed: Merge
wiggler elements in
simulationsStudy the evolution of the bunch shape during IBS: generation of non-Gaussian tailsIBS theoretical models: include
betatron couplingM. Pivi, F. Anotniou, Y. Papaphilippou (CERN)IBS evaluation: Long Term Plans
Slide16Electron 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.
Slide17Recommendation of Electron Cloud Mitigations
17
Clearing Electrodes
KEKB
Grooves w/TiN coatingClearing ElectrodeCESRTAGrooves on Cu
Stable Structures
Reliable Feedthroughs
Manufacturing Techniques
& Quality
amorphous-Carbon
Slide18Preliminary C
ESR
TA results and simulations suggest the possible presence of
sub-threshold
emittance growthFurther investigation requiredMay require reduction in acceptable cloud density a reduction in safety marginAn 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 RecommendationDrift*DipoleWigglerQuadrupole*Baseline Mitigation ITiN CoatingGrooves with TiN coatingClearing ElectrodesTiN CoatingBaseline Mitigation IISolenoid Windings
Antechamber
AntechamberAlternate 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 PlanGlobal 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
Slide19Mitigations: Wiggler Chamber with Clearing Electrode
Thermal spray tungsten electrode and Alumina insulator
0.2mm thick layers
2
0mm wide electrode in wigglerAntechamber full height is 20mmJoe Conway – Cornell U.
Slide20Mitigations: 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 chamberJoe Conway – Cornell U.
Slide21Electron cloud assessment for 2012 TDR: P
lans
Photon generation and distribution
PI: Cornell U.
In BENDs with groovesPI: LBNLIn WIGGLERS with clearing electrodesPI: SLACIn DRIFT, QUAD, SEXT with TiN coatingPI: Cornell U.Input cloud density from build-upPI: SLACElectron cloud Build-up Photon distribution Beam Instability
Slide22Photon 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.
Slide23Electron 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.
Slide24Quadrupole in wiggler section
The calculated
beampipe
-averaged cloud densities does not reach equilibrium after 8 bunch trains.
J. Crittenden, Cornell U.
Slide25Quadrupole in wiggler section
Electron cloud density (e/m
3
) Electron energies (eV
) J. Crittenden, Cornell U.
Slide26Sextupole in TME arc cell
Electron cloud density (e/m
3
) Electron energies (eV
) J. Crittenden, Cornell U.
Slide27Clearing electrode in wiggler magnet
Modeling of clearing electrode: round chamber is used
Clearing Field (left) & potential (right)
L. Wang, SLAC
Slide28detail
+600V
0v
+600V
+400V+100V-300V-600VL. Wang, SLAC
Electrodes with negative (above) or positive (below) potential
Slide29Completing 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 ...)
Slide30CLIC 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 othersNeed for an up-to-date R&D program to:systematically evaluate the electron cloud build-up and instabilities in the present DR configurationproperly select mitigation techniques to be implemented in each of the DR regionsovercome the beam instability and excessive heat loads
Slide31Summary
Intra-Beam Scattering codes in agreement with theoretical models
Estimations for Super-B and SLS,
CesrTAPlans 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
Slide32Back up slides
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)
Slide34Computational speed
(CMAD)
IBS simulations: computing time per turn,
Super-B lattice
(1582 ring elements)Mauro Pivi, CERN, CLIC collaboration341 processor64 processors100,000 macroparticle200 sec18.5 sec300,000 macroparticle540 sec24.4 secideal
e- cloud simulations
IBS:
Super-B, 100,000 macrop
IBS: Super-B, 300,000 macrop
Room for code optimization
CMAD
Slide35Intra-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 couplingPlans for IBS evaluation
Slide36Previous
work
: SIRE
IBS Distribution study D: IBSParameterValueEq. ex (m rad)2.001e-10Eq. ey (m rad)2.064e-12Eq. sd 1.992e-3Eq. sz (m)1.687e-3Parameterc2999
Confidence
Dp/p3048.7
<1e-15X1441.7<1e-15
Y1466.9<1e-15
A.
Vivoli
, Y.
Papaphilippou
Slide37Structured Evaluation of EC Mitigations
Nov 3-4, 2011 CLIC coll. meeting
Global Design Effort
37
Criteria for the evaluation of mitigations: Working Group ratingEfficacy of MitigationCostsRisksImpact on MachineRating10144Normalized Weighting0.530.050.210.21
Slide38EC 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%CostDesign and manufacturing of mitigationMaintenance of mitigationEx: Replacement of clearing electrode PSOperationalEx: Time incurred for replacement of damaged clearing electrode PS
Risk
Mitigation manufacturing challenges:
Ex: ≤1mm
or less in small aperture
VCEx: 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
electrodesImpact on opticsEx: x-y coupling due to solenoidsOperationalEx: NEG re-activation after saturationNov 3-4, 2011 CLIC coll. meetingDedicated ILC DR Working Group Workshop Meeting to evaluate technologies and give recommendation on electron cloud mitigations
Slide39Bends: Overall average EC density: all cases
(QE=0.05)
M. Furman, LBNL
Slide40Methodical 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 ringCharacterize the electron cloud (EC) effect in field free regions, dipole, quadrupole, sextupole and wiggler regionsEstimate effect of antechamber and photon stop designs on EC build-upPerform parameter space studies: vacuum chamber radii, base vacuum pressure, scan of the secondary electron yield and beam parameters, antechamber and photon stop designEstimate the single-bunch instability threshold by simulations and for a realistic CLIC damping ring latticeInvestigate coupled-bunch instability by simulations: quantify growth rate and address feedback systemDefine the maximum acceptable secondary electron yield SEY level, above which the beam would be unstable
Slide41Phase II. R&D on mitigations and recommendation:
Estimate
beneficial effect of solenoid field in field free
regionsInvestigate efficacy of technical mitigations on suppressing electron cloud build-up by simulationsE
xperimental R&D effort on mitigations tailored to the CLIC DR : amorphous Carbon, NEG and TiN coating, clearing electrodes, groovesEvaluate impact on impedance for possible mitigations: all coating options, clearing electrodes, grooves and photon stopsGive recommendation for technical mitigations for each machine regionGive recommendation on the design and specifications of mitigationsMethodical Electron Cloud evaluation for CLIC DR: Major Research Goals.
Slide42Change 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 …
Slide43CLIC 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
Slide44CLIC 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
Slide45CLIC DR Meetings Schedule
Date
Meeting
Wednesday 23
rd MayBDWednesday 6th JuneTS and BDTentative: Wednesday 13th JuneBDTentative: Wednesday 27th JuneTS and BD(BD = Beam Dynamics , TS = Technical Systems)Join us on the next DR meeting!