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International Linear Collider DR electron cloud R&D effort 1 st part: Tests in PEP-II. M. Pivi L. Wang, D. Arnett, G. Collet, R. Kirby, F. King, T. Markiewicz, B. McKee, M. Munro, N. Phinney, T. Raubenheimer, J. Seeman (SLAC), F. Le Pimpec (PSI) ECLOUD 07 - PowerPoint PPT Presentation
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9-12 April 2007
International Linear Collider DR electron cloud R&D effort1st part: Tests in PEP-IIM. Pivi
L. Wang, D. Arnett, G. Collet, R. Kirby, F. King, T. Markiewicz, B. McKee, M. Munro, N. Phinney, T. Raubenheimer, J. Seeman (SLAC), F. Le Pimpec (PSI)
ECLOUD 07Daegu
S. Korea
Courtesy P. Garbincius
• Effort started in 2003 with extensive simulations of electron cloud
build-up in DR including quadrupole and wigglers regions, and
simulations to characterize the single-bunch instability threshold
• International collaboration R&D effort: 2005-2006 simulation
campaign culminating in the recommendation for the damping ring
circumference reduced from 17 km to 12km [electron cloud safe],
then further reduced to 6km [red flag for electron cloud].
• Although an electron cloud is expected in the 6km positron Damping
Ring, simulations give increased confidence on possible remedies as
clearing electrodes and grooves.
• Substantial R&D effort is needed to confirm possible mitigation
techniques.
ILC DR Electron cloud simulation historyILC DR Electron cloud simulation historyILC DR Electron cloud simulation historyILC DR Electron cloud simulation history
Compare options: simulations historyCompare options: simulations historyCompare options: simulations historyCompare options: simulations history
Cloud density near (r=1mm) beam (m-3) before bunch passage, values are taken at a cloud equilibrium density. Solenoids decrease the cloud density in DRIFT regions, where they are only effective. Compare options LowQ and LowQ+train gaps. All cases wiggler aperture 46mm.
Global ILC R&D programIn progress:- At KEKB: in situ Secondary Electron Yield (SEY) measurements, ante-
chamber, Cu, TiN and NEG chambers. PLANNED: Clearing electrodes in wiggler.
- At SLAC: SEY of samples in accelerator beam line, rect. groove chambers, TiN chambers.
PLANNED: Clearing electrodes and grooves in bends.
Planned:- SPS and PS: LHC pre/injectors. Scrubbing runs and several mitigation
techniques are under evaluation.- Daphne: positron ring limited in current. TiN in aluminum wiggler
sections.
Proposed:- CesrTA: suppression techniques in wigglers (ILC damping ring
wigglers). Electron cloud build-up and instability with ultra-low emittancies close to the ILC DR.
- KEKB: Low emittance operation for electron cloud tests
• R&D Goals:– Estimate e-cloud build-up and single-bunch instability thresholds– Reduce surface secondary electron yield (SEY) below electron cloud
threshold for ILC DR: SEY ≤ 1.2
• Surface approaches– Thin film coatings– Electron and photon surface conditioning– Clearing electrodes– Grooved surfaces
• Projects:– ONGOING: conditioning TiN and NEG coatings in PEP-II straights– ONGOING: rectangular groove chambers in PEP-II straights– PLANNED: clearing electrode chamber in magnets– PLANNED: triangular groove chamber in magnets
E-cloud and SEY R&D Program SLAC
SEY GROOVE 1 GROOVE 2FLAT 1 FLAT 2
COLLECTORSENERGY ANALYZER
THERMOCOUPLES
GROOVE CHAMBERS EXPERIMENTSEY TEST STATION
PEP-II test chambers installationPEP-II test chambers installationPEP-II test chambers installationPEP-II test chambers installation
SEY station can be used to expose samples to PEP-ii beam environment and then measure samples in lab (transport in load-lock)
Grooved and Flat chambers installed to measure performance inPEP-ii beam environment
TiN/Al sample exposed to SR
PEP-II LER sideRF seal location
SEY TESTS TiN and NEGSEY TESTS TiN and NEGSEY TESTS TiN and NEGSEY TESTS TiN and NEG
Expose samples to PEP-II LER synchrotron radiation and electron conditioning. Then, measure Secondary Electron Yield (SEY) in laboratory. Samples transferred under vacuum.
Complementary at SPS and KEK studies
20mm
Project 2: chamber with coating samples.
e+
sample supports and transferring systems
45o position
0o position
PEP-II
SEY test station in PEP-II LERSEY test station in PEP-II LERSEY test station in PEP-II LERSEY test station in PEP-II LER
45o position
0o position
SEY test station in PEP-II LERSEY test station in PEP-II LERSEY test station in PEP-II LERSEY test station in PEP-II LER
45o position
0o position
SEY chamber instrumentation: SEY chamber instrumentation: e- energy analyzere- energy analyzerSEY chamber instrumentation: SEY chamber instrumentation: e- energy analyzere- energy analyzer
R. Kirby and M. P. SLAC, based on K.Harkay and R.Rosenberg design
p.14
Design- Fin ExtrusionsDesign- Fin Extrusions
FIN TIPS= I.D. OF CHAMFAN HITS HERE FIRST
LIGHT PASSES THRU SLOTS BETW FINSBECAUSE FAN IS “THICKER” THAN FIN
FAN EVENTUALLY HITS “BOTTOM” OF SLOT FOR FULL SR STRIKE
VIEW IS ROTATED 90 CCW FROM ACTUAL FAN ORIENTATION
p.15
Design- Fin ChamberDesign- Fin Chamber
Chambers are constructed of Al extrusions machined to length with end preps for masks & flanges.
Al extrusions were chosen for their economy and ease of manufacture
Bonus - cooling is integral to the cross section, not welded to the outside
Flanges are bi-metal Atlas flanges that are welded directly to chamber
Insufficient space between the chamber and the flange knife edge for a bi-metal transition
Bottom sides of chambers are perforated at the ports Inside surfaces are TiN coated
Reduce thermal outgassing & PSD Reduce secondary electron yield
Fin chamber weight ~ 32 lbs
p.16
Design- Port DetailDesign- Port Detail
4” port shown here, 500 holes, 25 x 20, holes 1.6 mm
1.5” port hole pattern is 50 holes, 10x5, holes 1.6 mm
Instrumentation: collector plate inside portInstrumentation: collector plate inside portInstrumentation: collector plate inside portInstrumentation: collector plate inside port
Chamber samples: SEY after TiN coating Chamber samples: SEY after TiN coating before installation in PEP-II before installation in PEP-II Chamber samples: SEY after TiN coating Chamber samples: SEY after TiN coating before installation in PEP-II before installation in PEP-II
Installation in PEP-II LERInstallation in PEP-II LERInstallation in PEP-II LERInstallation in PEP-II LER
Fin chamber
Flat chamber
p.20
Design – Existing Ring LayoutDesign – Existing Ring Layout
LER DIRECTION
ELEVATION VIEW
PLAN VIEW
BEND B1
AISLE SIDE
TIN/Al GROOVE/FLAT CHAMBERS HERESEY CHAMBER HERE
SEY test chamber samples: SEY before installation in PEP-II
LER #1 and #2 samples are then inserted in the PEP-II stainless steel chamber respectively in the plane of the synchrotron radiation fan (0o position) and out of this plane (45o position)
Secondary Yields after two months in PEP-II LER
LER#1
XPS Before installation After exposure in PEP-II LER for 2 months (e dose 100mC/mm^2)
Different from electron conditioning in laboratory setup where carbon crystals grows! Carbon is strongly reduced if exposed to beam. Same for LER #1 and #2 samples.
Surface analysis: Carbon content decrease
+214 hours at 1.1e-9 torr, 10:1 H2:COAfter 2 months conditioning in PEP-II
SEY after exposure to vacuum
(214 = 52 hours in PEP-II no beam +162 in laboratory setup)
Measured electron energy distribution
Compare vacuum chamber e- currents
Measured e- current in TiN/Al fin/flat chambers << StSt chamber. PEP-II LER current still raising (2.7A 4A).
groove1 groove2 flat2 flat1
18 March 2007
Solenoid ON at fin/flat chambers location
Switched external solenoid winding ON (10A Bz=20 Gauss). Ibeam = 2.2A. Note: at ~20 Gauss, photoelectrons should dominate with respect to secondary electrons..
10 15 20 250
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2x 10
14
S (m)
Ph
oto
n d
ensi
ty (
ph
oto
ns
m-1
s-1)
Photon Density for 1mA beam
G1
G1
F1
F2
0 500 1000 1500 2000 25000
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Beam Current (mA)
Ele
ctro
n C
urr
ent
(10
-6A
/cm
2)
TiN Groove 1TiN Groove 2TiN Flat 1TiN Flat 2Stainless Steel
Photon electron dominant ?
Preliminary benchmark with CLOUDLAND
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5 3
Ib(A)
Ie
SEY=1.3, R=0.001 SEY=1.2, R=0.001 Flat 2
SEY=1.3,R=0.001 SEY=1.2, R=0.0005
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5 3
Ib (A)
Ie
SEY=1.2, R=0.001 SEY=1.1 R=0.001 Flat 1
SEY=1.3, R=0.001 SEY=1.2 SEY=0.0005
Flat 1 Flat 2
In simulation, the SEY and the number of photon electrons are varied
For the Flat chamber, the SEY is around 1.1~1.2
L.Wang SLAC
Flat chamber
0
0.5
1
1.5
2
2.5
3
0 0.5 1 1.5 2 2.5 3 3.5
I (A)
Ie
SEY=1.2 SEY=1.1 Flat 2 SEY=1.3
This plot only show the SEY effect, R=0.001 for all of them
(R=e/p/m)
Simulation: - Uniform photoe- distribution- Electron current at the wall
Grooved chamber
0
0.5
1
1.5
2
2.5
3
3.5
4
0 0.5 1 1.5 2 2.5 3
I (A)
Ie
Groove 1 Groove 2 SEY=1 R=0.004 SEY=1 R=0.005
For the grooved chamber, the SEY is ~1
Simulation: - Uniform photoe- distribution- Electron current at the wall
SEY estimation
500 1000 1500 2000 2500 30000
2
4
6
8
10
12
14
Beam Current (mA)
No
rmal
ized
Ele
ctro
n C
urr
ent
TiN Groove 1TiN Groove 2TiN Flat 1TiN Flat 2
0 500 1000 1500 2000 25000
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Beam Current (mA)
Ele
ctro
n C
urr
ent
(10
-6A
/cm
2)
TiN Groove 1TiN Groove 2TiN Flat 1TiN Flat 2Stainless Steel
Raw data
...)(sec ondaryrmnonlinerteII bphotone
Ratio of Secondary to photoelectronsTotal electrons
Grooved Chamber has more photon electrons for some reason, but Flat Chamber has more secondary electrons, hence a higher SEY. This agree with simulation.
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5 3
I (A)
Ie
New Model
Y. Suetsugu, APAC07
0 500 1000 1500 2000 25000
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Beam Current (mA)
Ele
ctro
n C
urr
ent
(10
-6A
/cm
2)
TiN Groove 1TiN Groove 2TiN Flat 1TiN Flat 2Stainless Steel
PEPII Exp.
KEKB Exp.
Simulation closer to the experimental setup:- Photo e- on the chamber side-Collector on bottom chamber
Need more detail study
Work in progressWork in progressWork in progressWork in progress
• Electron signal in flat & fin chambers is much lower than stainless steel chamber.
• Electron signal in flat chambers is lower than fin chambers:– Photoelectron dominant in fins?– Fin chambers efficient photon absorbers?
• Simulation campaign starting:– Fitting stainless steel data to parameterize SEY– Fitting to flat & fin chamber data:
• Low SEY in flat chambers and grooved chambers between 0.9~1.2
• Appear to have higher photo e- rate in fin chambers
– Need ray tracing of photons to understand fin chamber
More input would be welcome
Plan for future workPlan for future workPlan for future workPlan for future work
Simulations:
• Systematic simulation effort starting • Further code benchmarking will be done
Experimental
• Conditioning and recontamination studies
• Insertion in beam line of non-evaporable getter NEG samples
• Insertion of samples with different materials: Cu, Stst, Al
• Study asymptotic conditioning effect: coating the stainless steel chamber with TiN (and NEG).
• Testing of chambers with NEG and clearing electrodes
Outstanding e-cloud questions Outstanding e-cloud questions Outstanding e-cloud questions Outstanding e-cloud questions Simulations
• Are the build-up codes sufficiently developed and benchmarked?
• Are the instability code sufficiently developed and benchmarked?
• What is the SEY threshold in the ILC DR configuration 3ns bunch spacing? – More code benchmarking needed
• In the presence of an electron cloud: is the dynamic aperture preserved at injection? – Large beam sizes no instability, but incoherent tune shift, ..
• Incoherent emittance growth below threshold, is it a real effect?
Remedies
• Is TiN thin film resistant after long term exposure?
• How to minimize vacuum recontamination (SEY) effects?
• What coating: TiN or NEGs (TiZrV)
• Do we need ultra-small emittance facilities to run electron cloud tests? CesrTA/KEKB
• Dependence of the SEY with NEG activation cycles? (highly requested by CERN!)
• Do we need to test clearing electrodes to suppress the electron cloud?
• Is TiN coating sufficient in wigglers?
• Measured trapping and accumulation of electrons in quadrupoles (sextupoles)? Is this an issue per se?
41
Milestones to the ILC Engineering Design Report (EDR)
1. Characterize electron-cloud build-up. (Very High Priority)
2. Develop electron-cloud suppression techniques. (Very High Priority)
Priority: characterize coating techniques and testing of conditioning and recontamination in situ.
Clearing electrodes concepts by installation of chambers in accelerators. Characterization of impedance, HOM and power load deposited to the electrodes.
Groove, slots and other concepts. Characterization of impedance, and HOM.
3. Develop modeling tools for electron-cloud instabilities. (Very High Priority)
4. Determine electron-cloud instability thresholds. (Very High Priority)
Characterization the electron cloud instability: various codes in use PETHS, HEAD-TAIL, WARP/POSINST, CMAD
SummarySummarySummarySummary
• Installed 5 chambers in PEP-II in January 2007
• Directly measured secondary electron yield of ~0.9 of TiN samples after exposure to beam. [Steering the ILC R&D effort in the direction of fully characterizing coating mitigation techniques..]
– Recontamination studies ongoing
• Electron signal in Fin & Flat chambers is much lower than stainless steel chamber
• Initial simulations: consistent with high SEY in Stainless steel chamber and low SEY in Fin & Flat TiN/Al chambers
– Systematic simulation effort ongoing to parameterize fin & flat chambers results
Thanks To contributors and collaborators: L. Wang, T. Raubenheimer,
D. Arnett, G. Collet, R. Kirby, N. Kurita, B. Mckee, M. Morrison, G. Stupakov, N. Phinney, J. Seeman (SLAC), M. Palmer, D. Rubin, D. Rice, L. Schachter, J. Codner, E. Tanke, J. Crittenden (Cornell), J. Gao (HIPEP), A. Markovic et al. (Rostock Univ.), M. Zisman, S. De Santis, C. Celata, M. Furman, J.L. Vay, S. De Santis (LBNL), K. Ohmi, Y. Suetsugu (KEK), F. Willeke, R. Wanzenberg (DESY), J.M. Laurent, A. Rossi, E. Benedetto, F. Zimmermann, G. Rumolo, J.M. Jimenez, J-P. Delahaye (CERN), A. Wolski (Cockroft Uniiv.), B. Macek (LANL), C. Vaccarezza, S. Guiducci, R. Cimino, P. Raimondi (Frascati), et many other colleagues…