groove mitigation and plans
DESCRIPTION
Groove Mitigation and Plans. M. Pivi and L. Wang (SLAC) Y. Suetsugu, H. Fukuma (KEK) M. Palmer (Cornell) G. Arduini, E. Chapochnikova (CERN) AEC09 CERN 12-13 October 2009. Grooves as mitigation. - PowerPoint PPT PresentationTRANSCRIPT
AEC09, CERNMauro Pivi, SLAC
Groove Mitigation and Plans
M. Pivi
and L. Wang (SLAC) Y. Suetsugu, H. Fukuma (KEK) M. Palmer (Cornell) G. Arduini, E. Chapochnikova (CERN)
AEC09CERN
12-13 October 2009
AEC09, CERNMauro Pivi, SLAC
Grooves strongly damp electron multiplication by trapping mechanism. Most efficient schemes are:
• Rectangular shape in field-free sections• Triangular shape in magnets
Showing here:• Early SEY measurements on test samples, 2006• PEP-II groove chambers, 2007• KEKB groove in wiggler, 2008• CesrTA groove in chicane, 2009
Grooves as mitigation
AEC09, CERNMauro Pivi, SLAC
Special surface profile design, Cu OFHC. EDM wire cutting. Groove: 0.8mm depth, 0.35mm step, 0.05mm thickness.
1 mm
Groove samples SEY Groove samples SEY measurements, SLACmeasurements, SLAC
M.Pivi and G. Stupakov, SLAC
Tested a variety of grooved samples with several different geometries
Un-coated copper sample SEY < 0.8. Smaller SEY~0.6 with deeper grooves
Un-coated copper sample SEY < 0.8. Smaller SEY~0.6 with deeper grooves
PEP-II chamber test samples
PEP-II chamber test samples
Ref: A. Krasnov LHC-Proj-Rep-617
AEC09, CERNMauro Pivi, SLAC
Design - Groove Extrusions - SLAC
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
Linear Collider R&D: Built Groove chambers by Al extrusion, TiN coated and installed in straight section PEP-II LER for ILC tests.
M. Pivi et al, SLAC
AEC09, CERNMauro Pivi, SLAC
Groove Chambers in PEP-II
Standard (flat) chambers installed as reference.
All chambers TiN coated
4 chambers alternating groove and standard (flat or smooth) chambers in PEP-II beam line, straight section.
e+
Grooved chamber Flat
chamber
Electron detectors
AEC09, CERNMauro Pivi, SLAC
Groove Chambers in PEP-II
• Groove chambers in field-free section, a factor ~20 lower e- cloud current• All 4 chambers re-deployed to CesrTA
AEC09, CERNMauro Pivi, SLAC
Grooves in dipole magnet
M. Pivi and L. Wang design, SLAC
Grooves located on upper and lower side of chamber where e- cloud develops. Include diagnostics.
• TiN-coated• Re-deployed to CesrTA• Grooves + TiN chamber best
performances in ongoing chicane tests
Dipole Mitigation Comparisons
• Current scan in L3 Chicane, 1x45 e+, 14ns, 5GeV– Note: Al signal is divided by 20 to show on the same scale– Grooved chamber has
5mm deep 20° triangular grooves with TiN coating
– Performance:• TiN+Grooves
significantly better than TiN alone
• Both TiN and groovessignificantly outperformthe bare Al surface, as expected
CesrTA Mitigation Studies: LCWA09 M. Palmer Cornell
9
4ns
Al TiN
Grooves + TiN
• Chicane B-field Scans– 1x45x1 mA, 4ns, 5GeV, e+– Resonance structure– Plots show
• Central collector (near beam axis)• Collectors near edge of vacuum
chamber• 17 collectors in each RFA
M. Palmer Cornell
Mauro Pivi, SLAC
Grooves tests in KEKB Groove and smooth inserts coated with TiN
– 5mm groove insert (Left) TiN-coated, manufactured by SLAC
– Smooth insert (Right) used as reference– Swapped at same location in KEKB wiggler
– Located on one side of chamber opposite to collector
M. Pivi, L. Wang (SLAC) Y. Suetsugu and H. Fukuma (KEK)
Mauro Pivi, SLAC
Electron Currents 1585 bunches(Bs ~ 6 ns)~1600 mAVr = 0 V
Y. Suetsugu and H. Fukuma (KEK), M. Pivi, L. Wang (SLAC)
AEC09, CERNMauro Pivi, SLAC
Smaller Grooves
Y. Suetsugu, H. Fukuma KEK, M. Pivi, L. Wang SLAC
New smaller ~2mm groove SLAC-KEK design. Ongoing tests at KEKB.
Sharpness of groove geometry can be a manufacturing challenge due to demanding e- cloud tolerances
AEC09, CERNMauro Pivi, SLAC
Groove Tests in the SPS
Planning for tests in SPS dedicated area: • Depth of groove limited to 1 mm due to vacuum
chamber aperture requirements.• Stainless steel insertion• Tight tolerances on roundness of groove tips and
valleys: < 100um.• Groove on one side of test chamber only• Insertion in existing liner or modified liner
AEC09, CERNMauro Pivi, SLAC
Groove Tests in the SPS
SPS liner for e- cloud tests
AEC09, CERNMauro Pivi, SLAC
Groove Tests in the SPS
Liner for SPS tests
Sep 2009
AEC09, CERNMauro Pivi, SLAC
Groove Tests in the SPS
St st. Groove insert bolt to liner
Variable incursion into chamber, actually 1.5mm
AEC09, CERNMauro Pivi, SLAC
• Back-up: 1.9mm aluminum + coating grooves (pictures above),
manufactured at SLAC. Extruded aluminum groove.
0 100 200 300 400 500 600 7000.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Energy (eV)
SE
Y
0=1.50,Height=1.9mm, =200
Flat surfacer=0.14mm,B=2 Teslar=0.14mm,B=0.2Teslar=0.09mm,B=2 Teslar=0.09mm,B=0.2Teslaaverage,B=2 Tesla
Lanfa Wang, SLAC
Tip Valley
Aluminum triangular groove, SLAC. Depth 1.9mm, Opening angle 20o, radius top 95um, radius valley 144um
Mauro Pivi - SLACApril 2008
Tip
Extruded aluminum insertion
AEC09, CERNMauro Pivi, SLAC
Impedance enhancement factor for the triangular grooved surface with round tips. Note that this is valid for frequencies ω such that c/ ω >> W; for example, for W~3mm this means <6e11 Hz.
ref. [L. Wang et al. FRPMS079, Proceedings of PAC07.]
Effect of triangular grooves on ImpedanceEffect of triangular grooves on Impedance
L. Wang et al. SLAC
Linear Collider R&D - Electron Cloud Working Group Charges
• To evaluate electron cloud mitigation techniques, simulations and code benchmarking for the AD&I option. In particular, evaluate the differences between mitigations as grooves clearing electrodes, coating (TiN, TiZrV NEG and amorphous Carbon) regarding their feasibility, effectiveness, impact on the vacuum system, on the beam impedance and on costs, for different regions of the ILC DR as drifts, arc magnets and wigglers.
Working Group Charges
• Mitigation techniques might be different for different regions of the damping ring.
• To recommend a baseline solution along with alternate solutions for the electron cloud mitigations in the 6.4km Damping Ring.
Furthermore, evaluate:• The proposal and options to reduce the DR
circumference to 3.2 km.• The ‘upgrade’ potential from 6ns to 3ns bunch
spacing in a 3km DR, immediately identified as bottleneck.
• The current limits due to e-cloud for the 3.2 km DR.
Working Group Charges
Deliverable
Recommendation for the baseline and alternate solutions for the electron cloud mitigation in various regions of the ILC Positron Damping Ring.
Recommendation for mitigation table
DR element % ring Antechamber need
Coating Additional Mitigation
Remarks
DRIFT in STRAIGHT
33 No NEG Solenoid Grooves
DRIFT in ARC
56 Downstream of BEND only
NEG Solenoid Grooves
BEND 7 Yes TiN Grooves
WIGG 3 Yes TiN Electrodes
QUAD 1 Downstream BEND / WIGG
TiN Grooves
Preliminary table to be completed as input for Technical Design Phase. Goal is to turn all Red colors to Green as input for the recommendation.
Other mitigations under development (carbon coating CERN/CesrTA)
Report Document
• A document produced by the working group by FY10 including the research work, a clear set of criteria for the recommendation and the recommendation itself.
Report DocumentRecommendation on electron cloud mitigations for the ILC DRIntroduction 5Request from AAP 5Working Group Charges and Deliverables 5Introduction Electron Cloud effect 10 [Zimmermann / Furman]Mitigations description
Solenoid 10 [Seeman]TiN coating10 [Suetsugu]Carbon coating 10 [Calatroni / Palmer]NEG coating 10 [Malishev]Grooves and Impedance 10 [Pivi]Clearing Electrodes and Impedance 10 [Suetsugu]Feedback system 10 [J. Fox]Conditioning 10 [Pivi / Suetsugu]Other mitigations (more or less mature) 8
Overall Experience at CesrTA 20 [Palmer]Overall Experience at PEP-II 20 [Pivi]Overall Experience at KEK-B 20 [Oide]Overall Experience at SPS 20 [Rumolo / Arduini]
Report Document
ILC Damping Ring 15Layout and parameters 8 [Pivi / Guiducci]Photon and Photoelectron Production 10 [Dugan]Simulation build-up 20 [Demma / Furman]Simulation single-bunch instability 20 [Pivi]Impedance of mitigations 15 [Suetsugu / Bane]Integrate CesrTA results to DR 20 [Palmer]
Process for mitigations recommendation 20Set of criteria for a decision 20External Reviews and Meetings 20Mitigations cost 5 [Palmer]
Recommendation for Mitigations in the ILC DR 5Summary 5
AEC09, CERNMauro Pivi, SLAC
Summary
• Overall grooves had excellent performances with e- cloud reduction in field free, dipole and wiggler sections of PEP-II, KEK-B and CesrTA.
• Manufacturing groove insert for SPS tests. mm size grooves manufacturing challenge. Implementation in existing machines is challenging.
• Looking at reducing groove depth to ~mm in long structures for Linear Colliders Damping Ring.
• Recommendation for electron cloud mitigations in ILC DR.
AEC09, CERNMauro Pivi, SLAC
MAFIA simulations (A. Novokhatski) indicate that wake fields are not excited during the beam passage in PEP-II design. Very small losses at transition estimated 1.5E-04 V/pC. Quoting A. Novokhatski: actually, grooves may help damping the propagation of Higher Order Modes down the beam pipe (need of simulations)
Power losses due to image charge are contained (ex. PEP-II, dP/ds=1W/cm).
Wakefield simulations PEP-II design