Intrabeam Scattering Mauro Pivi MedAustron work made while at SLAC i n collaboration with T Demma Frascati amp LAL the ILC CLIC and ID: 812048
Download The PPT/PDF document "Electron Cloud in Positron Rings and" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Electron Cloud in Positron Rings and Intra-beam Scattering
Mauro Pivi, MedAustron - work made while at SLAC -
i
n
collaboration
with: T.
Demma
(Frascati & LAL), the ILC / CLIC and
SuperB
Working
Groups
,
colleagues
at
LBNL,
Cornell
University
and SLAC.
Slide2Intra-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.
Slide3IBS Formalisms, models and simulation tools
M.
Boscolo
, USR Workshop, Oct.30th 2012
3
Piwinski
,
Bjorken and Mtingwa formalisms First formalisms ‘70/’80 for calculating IBS growth rates in storage rings based for Gaussian bunch distributionsK. Bane modelHigh energy approximation for Gaussian beamsA. Chao modelNovel analytical model, coupled differential eqs. valid for Gaussian beamsSemi-analitical model Using fit parameters from simulations iteratively, estimate emittanceMonte Carlo macroparticle tracking code (T. Demma et al.)6-D Monte Carlo, realistic studies for non-Gaussian beam distributions‘IBS-Track’ based on Zenkevich-Bolshakov Algorithmaims at exploring final equilibrium for non-Gaussian beams. Tails.ex, ey and ez evolution in time
Methods
are in good agreement
Slide4During the
two particles
small angle collision, the
momentum
change for 1 particle
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 – Monte Carlo code based on Zenkevich-Bolshakov AlgorithmM. Pivi, December 2015
Slide5Intrabeam Scattering in SuperB LER
Parameter
Unit
Value
Energy
GeV
4.18
Bunch population
10
10
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)ms40/40/20 N. of macroparticles-105 N. of grid cells-64x64x64
Bane PiwinskiIBS-Track
Bane PiwinskiIBS-Track
T.Demma, INFN
December 2011
Slide6Emittance Evolution in SuperB LER
SuperB V12 LER
Nb= 2x10
10
- 12x10
10
F=10 tx = 10-1 x 40 ms ty = 10-1x 40 ms ts = 10 -1x 20 msT.Demma, INFNDecember 2011
Slide7Simulations for
SuperB
M.
Boscolo
, USR Workshop, Oct.30th 2012
7
The easy computable semi-analytical approach allows a quick scan of some key design parameters, such as the bunch population
Equilibrium horizontal emittance vs bunch currentEquilibrium longitudinal emittance vs bunch current
Slide8Intra-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 & MADAccelerator lattice uploaded from MADX filesBunch 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
Mauro
Pivi
, CERN, CLIC
May 9-11, 2012
M.Pivi
,
A.Chao
,
C.Rivetta
,
T.Demma
,
M.Boscolo
,
F. Antoniou
, K.Li, Y.Papaphilippou, K.Sonnad, IPAC2012T. Demma, M. Pivi
Slide9IBS modeling: animation
http://www-user.slac.stanford.edu/gstewart/movies/particlesimulation_animation/
IBS - SuperB LER
Parameter
Unit
Value
Energy
GeV
4.18
Bunch population10106.5 Circumferencem1257
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-TrackT. Demma (INFN), M. Pivi (SLAC)IBS-Track C-MADDecember 2011
Slide11Emittance
Evolution
in
SuperB
LER
M. Pivi (SLAC), T.
Demma (INFN)
Slide12IBS Distribution
study
:
tails
Parameter
c
2
799ConfidenceZ 1857.56<1e-6X 1455.68<1e-6Y 778.2280.6920
T.
Demma
(
INFN)
,
M
. Pivi (SLAC
)
Slide13SIRE: IBS Distribution
study
in
CLIC
DR:
tails
ParameterValueEq. ex (m rad)2.001e-10Eq. ey (m rad)2.064e-12Eq. sd 1.992e-3Eq. sz (m)1.687e-3Parameterc
2
999
Confidence
D
p
/p
3048.7
<1e-15
X
1441.7
<1e-15
Y
1466.9
<1e-15
A.
Vivoli
(CERN)
Slide14IBS - Swiss Light Source (SLS)
IBS_Track
, T
.
Demma
(INFN)
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.Comparison with experimental data at SLS: F. Antoniou et al. IPAC 2012-- 6×109 ppb-- 60 ×109 ppb-- 100 ×109 ppb
Slide15Summary IBS
Both tracking codes
(INFN/CERN
),
that implement the
Zenkevich-Bolshakov
algorithm, 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 codeComparison 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.15
Slide16In 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. decreasing
the collider performances.Electron cloud effect in proton and positron storage rings25 nsElectron cloud in the LHC25 ns
Slide17Surface measurements at SLAC. F. Le
Pimpec
et al.
For convenience the SEY maximum value is often quoted.
The Secondary Electron Yield (SEY) on a surface: Key Parameter for Electron
M
ultiplicationThe secondary electron yield (SEY) is the number of electrons emitted per primary incident electron. It depends on:the energy of the incident electronSurface treatment and history
Slide18Observations of Electron Cloud
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, DA
F
NE, CESRTA,
CERN
SPS and at LHC.H. Fukuma et al.J. Flanagan et al.
Slide19Electron cloud assessment Linear Colliders working group: Worldwide Laboratory
E
ffort
Development of mitigation techniques:
e
-
conditioning, surface coatings, clearing electrodes, grooves, solenoids
SEY measured on samples placed in accelerator environments: SLAC, CERN, KEK, CesrTA, DafneInstability simulations: to determine instability thresholdBuild-up & evolution simulations: fed with measured SEY to evaluate level of electron cloud in the acceleratorConverge to recommendation for adoption of mitigationsJan 18, 2010 ILC BAW-2Global Design Effort19
Slide20Electron 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. Flammini and R. Larciprete Phys. Rev. Lett. 109, 064801 – 2012
Slide21“Clearing” electrodes capture electrons in the time between bunches.
Electron Cloud
Technical Mitigations
Surface coating
with low Secondary Electron Yield material
Solenoid magnetic field modifies electron dynamics
Surface with grooves
confine electrons e-
Slide22Recommendation of Electron Cloud Mitigations
22
Clearing Electrodes
KEK
Grooves w/
TiN
coating, KEK/SLAC
CESRTAClearing ElectrodeGrooves on CuStable StructuresReliable Feedthroughs
Manufacturing Techniques
& Quality
amorphous-Carbon, CERN
Slide23Evaluation of Electron 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.
Slide24Beam 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)
Slide25Electron
Cloud
instability threshold
4.4e11
3.9e11
3.5e11
Cloud density (e/m
3)3.2 km ILC Damping RingInstability simulations for the International Linear Collider Positron Damping Ring. Instability threshold ~2×1011 e/m3
Slide26Build up simulations: Quadrupole in wiggler section
Electron cloud density (e/m
3
) Electron energies (
eV
)
J. Crittenden, Cornell U.
Slide27Sextupole in TME arc cell
Electron cloud density (e/m
3
) Electron energies (
eV
)
J. Crittenden, Cornell U.
Slide28Build-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
Slide29detail
+600V
0v
+600V
+400V
+100V
-300V
-600VL. Wang, SLACBuild-up simulations: Electrodes with negative (above) or positive (below) potential
Slide30Mitigations: Wiggler Chamber with Clearing Electrode
Thermal spray tungsten electrode and Alumina insulator
0.2mm thick layers
2
0mm wide electrode in wiggler
Antechamber full height is 20mm
Joe Conway – Cornell U.
Slide31Mitigations: 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.
Slide32Electron Cloud Mitigation Recommendation
Global Design Effort
32
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 PSRiskMitigation manufacturing challenges: Ex: ≤1mm or less in small aperture VC
Ex: C
learing
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 performanceEx: NEG pumping can have a positive effectEx: Vacuum outgassingImpact on machine impedanceEx: 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 Workshop at Cornell University, NY, USA 2010 on Recommendation on electron cloud mitigations
Slide33Structured Evaluation of EC Mitigations
Nov 3-4, 2011 CLIC coll. meeting
Global Design Effort
33
Criteria for the evaluation of mitigations: Working Group rating
Efficacy of Mitigation
Costs
RisksImpact on MachineRating10144Normalized Weighting0.530.050.210.21
Slide34C
ESR
TA
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 marginAggressive 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 WindingsAntechamberAntechamberAlternate MitigationCarbon coating/ NEG CoatingTiN CoatingGrooves 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
34
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
Slide35Completing evaluation for ILC
With recommended mitigations
the ring-average cloud density
is
4
×10
10 e/m3, well below the instability threshold of 2
×1011 e/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 SuperKEKB and Daphne.
Slide36e-
Cloud
@ DAFNE: Clearing
Electrodes
D.
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
cloud
evolution
with clearing
electrodes
(POSINST)
0 50 100 150 200 250 300 350
Time (ns)
Theo
Demma
, INFN
Slide37Clearing electrodes in DaF
ne
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)Simulated evolution of the cloud density for different electrode voltage.
Slide38Horizontal
fractional tune as a function of bunch
number along train of bunches.
Electrodes OFF
Electrodes ON
Effect of clearing electrodes on beam in
Da
FneBeam dimension (um) at the Synchrotron light monitor turning all electrodes progressively off.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
Slide39Electrod cloud mitigations in Da
F
ne
: clearing electrodes
Clearing electrodes installed in
Da
F
ne dipoles and wigglersExperimental 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.
Slide4040
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:
Beam energy E[GeV]
6.7
circumference L[m]
1200
bunch population N
b
5.7x10
10
bunch length
σ
z
[mm]
5
horizontal emittance
ε
x
[nm rad]
1.6
vertical emittance εy [pm rad]4hor./vert. betatron tune Qx/Qy40.57/17.59synchrotron tune Qz0.01hor./vert. av. beta function25/25momentum compaction 4.04e-4Input parameters (LNF conf.) for CMAD=5x1011=4x1011=3x1011T. Demma: Preliminary results for SuperBVertical emittance growth induced by e-cloud
Slide4141
Snapshot of the electron (x,y) distribution
Density at center of the beam pipe is larger then the average value.
Buildup in Free Field Regions
Snapshot of the electron (x,y) distribution 50G solenoids on
Solenoids reduce to 0 the e-cloud density at center of beam pipe
Slide4242
Snapshot of the electron (
x,y
) distribution
“
just before
”
the passage of the last bunch
LER Arc quadrupole vacuum chamber (CDR)
dB
y
/dx=2.5T/m,
=99%
max
=1.2
center
average
Buildup in the SuperB arcs: Quadrupoles
Cloud density average in chamber and near beam center
Slide4343
Single Bunch Instability Threshold
June 2008
January 2009
March 2009
int
[10
15
m
-2
]
solenoids
int
[10
15
m
-2
] no solenoids
int
[1015m-2] solenoidsint [1015m-2] no solenoidsint [1015m-2] solenoidsint [1015m-2] no solenoidsSEY=1.195%0.062.10.092.50.222.799%0.020.250.040.30.04 0.7SEY=1.295%0.222.80.273.20.456.599%0.0450.710.060.820.072.4SEY=1.395%2.720.22.925.75.42599%0.943.21.34.14.513SuperB V12center 1012 [e-/m3]0.10.070.60.22.00.7th= 1012 [e-/m3]
Slide4444
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 ~10
12 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
Slide45Multi-particle code simulations
Mauro Pivi
IBS in Super-B; Theory compared with C-MAD and IBS-Track codes.
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 mitigationsElectron cloud: emittance growth with cloud density in Super-BC-MADT. Demma and M. Pivi, Collective effects in Super-B, IPAC 2010Electron cloud: clearing electrodes in Super-B+100V+1000V0V