Recent Experimental Results on Amorphous Carbon Coatings ......3 Conclusions and outlook Conclusions...

Recent Experimental Results on AmorphousCarbon Coatings for Electron Cloud Mitigation

ECLOUD ’10, Cornell University, Ithaca, New York USA

Christina Yin Vallgren

S. Calatroni, P. Chiggiato, P. Costa Pinto, H. Neupert, M. Taborelli,

W. Vollenberg

Vacuum, Surfaces and Coatings Group (VSC), TE-departmentSPS-U team: E .Shaposhnikova, G. Arduini, J. Bauche, F. Caspers, K. Cornelis,S. Federmann, E. Mahner, E. Metral, G. Rumolo, B. Salvant, F. Zimmermann

CERN, CH-1211, Geneva, Switzerland

October 8-12, 2010

MotivationExperiments

Conclusions and outlook

Outline

1 MotivationSPS-U: Super Proton Synchrotron UpgradeNew solution → Amorphous Carbon Coating

2 ExperimentsCoating ConfigurationsExperiments in the labImplementation in the SPS: E-cloud experimentsAgeing (increase of SEY) observation of a-C coating

3 Conclusions and outlookConclusionsOutlook

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SPS-U: Super Proton Synchrotron UpgradeNew solution → Amorphous Carbon Coating

Outline




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The goal of this work

SPS-U: make the SPS able to deliver the above nominal beams toLHC and reach maximum luminosity.

Find a solution to eliminate e-cloud in the SPS, which

can be implemented in the present SPS-dipoles withoutaperture reduction

does not require bake-out

is robust against air venting (maintenance, installation...)

has a long life time

The condition for the secondary electron yield to avoid e-cloud inSPS dipoles with nominal LHC beam is (G.Rumolo et al.)

δmax < 1.3

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Possible remedies for the electron cloud in the beam pipe:

Low Secondary Electron Yield (SEY) thin-film coatings

surface conditioning

clearing electrodes

chamber with grooves or slots

Ti-Zr-V film coating (implemented in straight sections of LHC) haveδmax = 1.1 after activation at temperature higher than 180◦C (24h).

But they cannot be applied to the SPS because the SPS magnet vacuum

chambers are not bakeable.

TiN works well under the effect of photon conditioning in situ.

But no photons in the SPS.

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Which material to start with:

Known facts

For air exposed stainless steel, Cu and Al δmax > 2.

In the periodic system, elements with fewer electrons (on theleft side) => lower SEY.

’Beam scrubbed’ surfaces are covered by more carbon(at least Cu and StSt).

Try Carbon, which has few electrons

SEY of graphite is much lower than diamond, so try to makegraphite-like coatings.

Graphite is not very reactive, should be less affected by airexposure.

Graphite-like Amorphous Carbon (a-C) Thin Film Coating.

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Which material to start with:

Known facts

For air exposed stainless steel, Cu and Al δmax > 2.

In the periodic system, elements with fewer electrons (on theleft side) => lower SEY.

’Beam scrubbed’ surfaces are covered by more carbon(at least Cu and StSt).

Try Carbon, which has few electrons

SEY of graphite is much lower than diamond, so try to makegraphite-like coatings.

Graphite is not very reactive, should be less affected by airexposure.

Graphite-like Amorphous Carbon (a-C) Thin Film Coating.

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Coating ConfigurationsExperiments in the labImplementation in the SPS: E-cloud experimentsAgeing (increase of SEY) observation of a-C coating

Outline




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Coating Configurations - DC magnetron sputtering

Different coating configurations were used:

Cylindrical tube with one graphite rod cathode (for lab samples forSEY investigation and vacuum characterization)

Liner in tube with 4 graphite rods (Lab samples, liner for e-cloudmonitors)

MBB magnet chamber in-situ (chamber in the dipole) withMulti-electrode geometry (Version I: coating in-situ in SPS dipoles)

MBB magnet chamber stand-alone with liner configuration(Version II: coating outside SPS dipoles)

Different discharge gases (Ne, Kr, Ar) and different coating parameters

(Temperature of substrate, discharge gas pressure, power) can be used.

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Cylindrical tube configurationLab samples for SEY and vacuum characterizations

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Liner in tube with 4 graphite rodsLab samples, liner for e-cloud monitors

The coating chambers were inserted in a solenoid and the magneticfield is parallel to the cathodes and chamber axis.The surface temperature can rise to 250◦C.

Four graphite rods were used to avoid coating in-homogeneity.

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Liner in tube with 4 graphite rodsLab samples, liner for e-cloud monitors

The coating chambers were inserted in a solenoid and the magneticfield is parallel to the cathodes and chamber axis.The surface temperature can rise to 250◦C.

Four graphite rods were used to avoid coating in-homogeneity.

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Coating for the Electron Cloud Monitor in the SPS

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Coating for the Electron Cloud Monitor in the SPS

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MBB magnet in-situ with Multi-electrode geometryVersion I: coating in-situ in SPS dipoles

The magnetic field of the dipole was used and was perpendicular

to the cathodes and chamber axis.

The power during coating was kept limited in order to avoidoverheating and damaging of the coil of the dipole.

Three MBBs have been coated.

Disadvantage: in-homogeneity.

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MBB magnet in-situ with Multi-electrode geometryVersion I: coating in-situ in SPS dipoles

The magnetic field of the dipole was used and was perpendicular

to the cathodes and chamber axis.

The power during coating was kept limited in order to avoidoverheating and damaging of the coil of the dipole.

Three MBBs have been coated.

Disadvantage: in-homogeneity.

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MBB magnet stand-alone with liner configurationVersion II: coating outside SPS dipoles

Use the same technique as for liner coating to coat thevacuum chamber outside the SPS magnet.

Three new MBBs have been coated.

Disadvantage: Cut-open SPS dipole magnet and reassembly.(Expensive process!)

Advantage: Perfectly homogeneous coating for large scaleproduction can be done in advance.

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MBB magnet stand-alone with liner configurationVersion II: coating outside SPS dipoles

Use the same technique as for liner coating to coat thevacuum chamber outside the SPS magnet.

Three new MBBs have been coated.

Disadvantage: Cut-open SPS dipole magnet and reassembly.(Expensive process!)

Advantage: Perfectly homogeneous coating for large scaleproduction can be done in advance.

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In the lab: The SEY as a function of PEP: power, p: pressure

200 400 600 800 1000 1200 1400 16000.6

0.7

0.8

0.9

1

1.1

Primary Energy (eV)

SE

Y δ

high P, med phigh P, high phigh P, low pmed P, low pmed P, med plow P, med p

Measured directly afterextraction from thedeposition chamberand transfer to theSEY apparatusthrough air.

The precision of thepresented SEY valuesis estimated to ±0.03.

δmax is between 0.9and 1.1 and Emax =300 eV. (not sensitiveto coating parametersas pressure, power.)

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In the lab: The SEY as a function of PEP: power, p: pressure

0.8 0.9 1 1.1 1.20

5

10

15

20

25

δmax

of a−C coatings

Nu

mb

ers

of

the

co

atin

gs.

To

tal:

90

sa

mp

les

Measured directly afterextraction from thedeposition chamberand transfer to theSEY apparatusthrough air.

The precision of thepresented SEY valuesis estimated to ±0.03.

δmax is between 0.9and 1.1 and Emax =300 eV. (not sensitiveto coating parametersas pressure, power.)

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Electron Cloud Monitor (ECM) in the SPS

Electron cloud current normalized withbeam intensity v.s time, measured byECM in the SPS.

3-4 batches of nominal LHC beam.(1.15 · 1011 protons/bunch)

0 1 2 3 4 5−6

−5

−4

−3

−2

−1

0

Time(h)

Log1

0(In

tEle

ctro

nCur

rent

/IntF

BC

T)

Normalized e−cloud from the MD runs

a-C nr1 tested in the SPSa-C nr2 tested in the SPSStainless Steel

SEY measurements in thelab.

0 200 400 600 800 1000 1200 1400 1600 18000.5

1

1.5

2

2.5

Primary Energy (eV)

SE

Y δ

a−C nr1 tested in the SPS: δ = 0.92a−C nr2 tested in the SPS: δ = 1.14Stainless Steel: δ = 2.25

Observe!

EC signal is 104 higher onStSt than a-C.

Low SEY ⇒ Low electroncurrent signal.

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Ageing observation of a-C liner in the ECM in the SPS

One a-C coated liner has been tested during 3 MachineDevelopment (MD) Runs with 3-4 batches of nominal LHC beamaccelerated to 450 GeV/c.

Vertical unit: nC/1010 protons perbunch

The a-C coated liner was kept inthe SPS for more than one yearoperation. (more than 2 months ofventing, maintenance,installation...)

No sign of ageing in the SPS.

0 1 2 3 4 5−1

0

1

2

3

4

5x 10−4

Time(h)

IntE

lectr

on

Cu

rre

nt/In

tFB

CT


a-C in MD1: 12 August, 2008a-C in MD2: 6-8 October, 2008a-C in MD3: 15-18 June, 2009

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0 1 2 3 4 5−1

0

1

2

3

4

5x 10−4

Time(h)

IntE

lectr

on

Cu

rre

nt/In

tFB

CT



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0 1 2 3 4 5−1

0

1

2

3

4

5x 10−4

Time(h)

IntE

lectr

on

Cu

rre

nt/In

tFB

CT



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Inspection of FIVE liners extracted from SPSOne Stainless Steel liner and four a-C coated liners

Liner SPS operation δinitial

StSt 1 year 2.25(Reference) (5 MD runs)

C-strip 1 year 0.92(a-C coating of 40mm width) (5 MD runs)

C-Zr 1.5 years 0.95(a-C on rough Zr coating) (9 MD runs)

CNe64 3 months 0.95(a-C coating) (2 MD runs)

CNe65 3 months 0.95(a-C coating) (2 MD runs)

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Three MBB dipoles have been coated with a-C coatingin-situ dipole (Version I) inserted in the SPS

Microwave transmission measurements detected e-cloud

related signal in the coated and uncoated magnets.

F. Caspers, S. Federmann

Dynamic pressure rise used to monitor the behavior of

the coated and uncoated magnets. 28 / 42




Three MBB dipoles have been coated with a-C coatingin-situ dipole (Version I) inserted in the SPS

Microwave transmission measurements detected e-cloud

related signal in the coated and uncoated magnets.

F. Caspers, S. Federmann

Dynamic pressure rise used to monitor the behavior of

the coated and uncoated magnets. 29 / 42




E-cloud related measurements/SEY measurements in thelab

Dynamic pressure rise between thecoated and uncoated magnets.

The nominal LHC beam: 1,2,3 and4 batches with 72 bunches at 25 nsspacing.

SEY measurements before/afterinsertion in the SPS.

0 200 400 600 800 1000 1200 1400 1600 18000.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

Primary Energy (eV)

SEY

δ

MBB magnet before insertion in the SPS: δ = 1.00MBB magnet after 1 year operation: δ = 1.33

No different in pressure rise.

SEY increases after extraction.

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E-cloud related measurements/SEY measurements in thelab

Dynamic pressure rise between thecoated and uncoated magnets.

The nominal LHC beam: 1,2,3 and4 batches with 72 bunches at 25 nsspacing.

Non-uniform coating color indicatesdifferences in thickness andpossibly composition.

Bad SEY is mostly due to thecoating configuration.

Coat MBB vacuum chamberstand-alone outside dipole!!!(Version II)

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ConclusionsOutlook

Outline




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ConclusionsOutlook

Conclusions

A-C thin films produced by d.c magnetron sputtering show areliable low initial SEY (well below δthreshold = 1.3).

A complete suppression of e-cloud can be achieved by coatingof liners with a-C.

The coating of liners does not show ageing (increase of SEY)after more than 1 year of exposure in the SPS.

Magnetron sputtered a-C film is a potential solution toeliminate e-cloud.

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ConclusionsOutlook

Conclusions





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ConclusionsOutlook

Conclusions





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ConclusionsOutlook

Conclusions




Magnetron sputtered a-C film is a potential solution toeliminate e-cloud. ✓

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ConclusionsOutlook

Outlook

The future activities will be focused on:

modifying the coating system in order to find an efficient andeconomical solution to coat beam pipes in a large scale withthe same quality of coating as in the ECMs.following the ageing development of the liners and getting adeeper understanding of a-C thin film both in the lab and inthe SPS.following the ageing development of the new version of MBBcoating and getting a deeper understanding of the relationshipbetween dynamic pressure rise and e-cloud effect.

The first implementation in a large scale with this type of a-Ccoating is now planned to be performed in the SPS magnet oftotal 200 m during the shutdown 2012.

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ConclusionsOutlook

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ConclusionsOutlook

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ConclusionsOutlook

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Thanks

Thanks for your attention ! and Questions

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Recent Experimental Results on Amorphous Carbon Coatings ......3 Conclusions and outlook Conclusions...

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