Groove Mitigation and Plans

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


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


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


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


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


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


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)


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


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



SPS liner for e- cloud tests



Liner for SPS tests

Sep 2009



St st. Groove insert bolt to liner

Variable incursion into chamber, actually 1.5mm


• 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


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


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.


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

Groove Mitigation and Plans

Documents

Transcript of Groove Mitigation and Plans