Progress on e-cloud effects (PS and SPS)

G. Iadarola, H.Bartosik, G. Rumolo, M. Taborelli, C. Yin Vallgren

Many thanks to:G. Arduini, T. Argyropoulos, T. Bohl, F. Caspers, S. Cettour Cave, K. Cornelis, H. Damerau,

M. Driss Mensi, J. Esteban Muller, S. Federmann, F. Follin, S. Gilardoni , B. Goddard, S. Hancock, W. Hofle, M.Holz, C. Lazaridis, L. Kopylov , H. Neupert, Y. Papaphilippou, M. Pivi, S. Rioja Fuentelsaz,

D. Schoerling , E. Shaposhnikova, , G. Sterbini, H. Timko

and all the PS and SPS operator crews

Outline

Electron cloud effects in the PS• Beam observation• Flat top instability• RF voltage optimization for e-cloud mitigation• Studies for the main magnets

Electron cloud effects in the SPS• Status for nominal intensity• Tests with higher intensity• “Doublet” beam for scrubbing• e-cloud measurement campaign• a-C coatings

Outline

Electron cloud effects in the PS• Beam observation• Flat top instability• RF voltage optimization for e-cloud mitigation• Studies for the main magnets

Electron cloud effects in the SPS• Status for nominal intensity• Tests with higher intensity• “Doublet” beam for scrubbing• e-cloud measurement campaign• a-C coatings

e-cloud in the PS

h=7b. sp. ≈ 330 ns (4 - 6 b.)

h=21b. sp.≈100 ns (18 b.)

h=42b.sp.=50 ns (36 b.)

h=84b.sp.=25 ns (72 b.)

Triplesplitting

Double splitting

Bunch shortening

Double splitting

e-cloud in the PS

h=7b. sp. ≈ 330 ns (4 - 6 b.)

h=21b. sp.≈100 ns (18 b.)

h=42b.sp.=50 ns (36 b.)

h=84b.sp.=25 ns (72 b.)

Triplesplitting

Double splitting

Bunch shortening

Double splitting

No e-cloud

e-cloud in the PS

h=7b. sp. ≈ 330 ns (4 - 6 b.)

h=21b. sp.≈100 ns (18 b.)

Triplesplitting

Double splitting

Bunch shortening

Double splitting

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Double splitting

Adiabatic shortening

Bunch rotation

b.l.≈14 ns

11 ns

4 ns

e-cloud in the PS

h=7b. sp. ≈ 330 ns (4 - 6 b.)

h=21b. sp.≈100 ns (18 b.)

Triplesplitting

Double splitting

Bunch shortening

Double splitting

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h=84b.sp. = 25 ns (72 b.)

Double splitting

Adiabatic shortening

Bunch rotation

b.l.≈14 ns

11 ns

4 ns

E-cloud expected and observed

e-cloud in the PS: beam observations

• Up to now e-cloud in the PS has never been a limitation for the production of the 25 ns LHC type beams

• In 2012, bunch by bunch emittance measurements performed in the SPS (intensities up to 1.45e11 ppb) never revealed any e-cloud signature on the emittance pattern coming from the PS

Measurements done on the SPS flat top with 1.45e11 ppb injected into the SPS

Horizontal Vertical

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

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Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

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First studies in: R. Cappi, M. Giovannozzi, E. Metral, G. Métral, G. Rumolo and F. Zimmermann, "Electron cloud buildup and related instability in the CERN Proton Synchrotron." Physical Review Special Topics-Accelerators and Beams 5.9 (2002): 094401.

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

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Bunch 10

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

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Bunch 16

• The risetime is decreasing along the train

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

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Bunch 22

• The risetime is decreasing along the train

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Bunch 28

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

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Bunch 34

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

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Bunch 40

• The risetime is decreasing along the train

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Bunch 46

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

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Bunch 52

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

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Bunch 58

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

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Bunch 61

• The risetime is decreasing along the train

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

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Bunch 67

• The risetime is decreasing along the train

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

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Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

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Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

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Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

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Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

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Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

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Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

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Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

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Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

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Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

These features look compatible with an e-cloud

driven instability

Transverse instability with “stored” beam

A possible reason of the absence of any degradation could be that the beam does not interact with the cloud for a sufficiently long time

If we “store” the beam for ~20 ms an horizontal instability is observed.

• The risetime is decreasing along the train

• Coupled bunch motion is clearly visible

These features look compatible with an e-cloud

driven instability

Good news: the new transverse feedback can delay this instability!

10 ms

See talk by G. Sterbini

Possible mitigation strategies: RF voltage program

Together with the RF experts, we could optimize the 40MHz voltage program in order to mitigate the e-cloud without affecting the beam quality

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H. Damerau, S. Hancock, T. Kroyer, E. Mahner and M. Schokker, Electron Cloud Mitigation by Fast Bunch Compression in the CERN PS (No. CERN-AB-2008-050).

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Possible mitigation strategies: RF voltage program

Together with the RF experts, we could optimize the 40MHz voltage program in order to mitigate the e-cloud without affecting the beam quality

H. Damerau, S. Hancock, T. Kroyer, E. Mahner and M. Schokker, Electron Cloud Mitigation by Fast Bunch Compression in the CERN PS (No. CERN-AB-2008-050).

Possible mitigation strategies: RF voltage program

Together with the RF experts, we could optimize the 40MHz voltage program in order to mitigate the e-cloud without affecting the beam quality

1.25e11 ppb

1.45e11 ppb

60b. schemes with shorter train (e.g. BCMS)

are less critical

To be addressed with simulations and measurements with particular focus on main magnets:• PyECLOUD modules for the

simulation combined function magnets have been developed and tested

• One magnet unit will be equipped for e-cloud detection during LS1 (see talk by S. Gilardoni)

e-cloud in the main magnets

We need to assess if with LIU beam parameters the observed instability (or other e-cloud effects) can degrade the beams on the timescale of the production cycle.

To be addressed with simulations and measurements with particular focus on main magnets:• PyECLOUD modules for the

simulation combined function magnets have been developed and tested

• One magnet unit will be equipped for e-cloud detection during LS1 (see talk by S. Gilardoni)

e-cloud in the main magnets

We need to assess if with LIU beam parameters the observed instability (or other e-cloud effects) can degrade the beams on the timescale of the production cycle.

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e-cloud in the main magnets

We need to assess if with LIU beam parameters the observed instability (or other e-cloud effects) can degrade the beams on the timescale of the production cycle.

[By Teddy Capelli EN/MME]

To be addressed with simulations and measurements with particular focus on main magnets:• PyECLOUD modules for the

simulation combined function magnets have been developed and tested

• One magnet unit will be equipped for e-cloud detection during LS1 (see talk by S. Gilardoni)

Outline

Electron cloud effects in the PS• Beam observation• Flat top instability• RF voltage optimization for e-cloud mitigation• Studies for the main magnets

Electron cloud effects in the SPS• Status for nominal intensity• Tests with higher intensity• “Doublet” beam for scrubbing• e-cloud measurement campaign• a-C coatings

e-cloud in the SPS: nominal bunch intensity

• In the past e-cloud has been strongly limiting the performances with 25 ns beams with detrimental effects both on vacuum and beam quality

• Scrubbing runs regularly performed over the years with evident beneficial effects on dynamic pressure rise and beam quality

Vertical emittance

2000 (1 batch 0.8x1011ppb)

400%

G. Arduini, K. Cornelis et al.

e-cloud in the SPS: nominal bunch intensity

• In the past e-cloud has been strongly limiting the performances with 25 ns beams with detrimental effects both on vacuum and beam quality

• Scrubbing runs regularly performed over the years with evident beneficial effects on dynamic pressure rise and beam quality

• Full characterization of the nominal 25 ns beams in the SPS (bunch by bunch emittance, tune, liferime vs. chrmoaticity) did not show any degradation due to e-cloud

Vertical

2012 (4 batches 1.15x1011ppb)

Tests with higher intensity

• In the last part of the 2012, MD sessions were dedicated to tests with higher intensity 25 ns beams (up to 1.45e11 inj.) with Q20 opticso Emittance blow up observed on trailing bunches of the last

batches

• But:o Machine never scrubbed for these intensitieso Possible other sources still to be investigated

Tests with higher intensity

• In the last part of the 2012, MD sessions were dedicated to tests with higher intensity 25 ns beams (up to 1.45e11 inj.) with Q20 opticso Emittance blow up observed on trailing bunches of the last

batches

• But:o Machine never scrubbed for these intensitieso Possible other sources still to be investigated

Two wire breakage during this tests. Bunch by bunch emittance measurements on full bunch train are extremely important to identify/study this kind of issues.Are we ready for higher intensities?

“Doublet” scrubbing beam• An important goal of the studies was the identification of a

possible dedicated scrubbing beam, showing an e-cloud threshold lower than the 25 ns beam.

• Simulations have shown that a possible candidate is 25 ns spaced train of doublets

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PyECLOUD simulation

Accumulation between subsequent turns

“Doublet” scrubbing beam• An important goal of the studies was the identification of a

possible dedicated scrubbing beam, showing an e-cloud threshold lower than the 25 ns beam.

• Simulations have shown that a possible candidate is 25 ns spaced train of doublets

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• Relatively simple production :o Inject long bunches from the PS (b. len.≈10 ns)o Capture in two SPS buckets (5 ns long)

“Doublet” scrubbing beam

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First 500 turns after inj.

• The production scheme has been successfully tested for a train of (2x)72 bunches with 1.7e11 p per doublet

• The possibility to inject more than one batch from the PS has been tested in Feb. 2013

2 s after inj.

“Doublet” scrubbing beam

It seems it works!!!MBA-like Stainless Steel liner

25ns standard (1.6e11p/bunch)

25ns “doublet” (1.7e11p/doublet)

• Clear enhancement observed both on e-cloud detectors and pressure in the arcs

25ns std. (1.6e11p/bunch)

(1.7e11p/doublet)25ns “doublet”

a-C coatings

• In 2012, amorphous carbon coatings have been validated as an e-cloud suppression technique, to be used if scrubbing will not be sufficiento Tests showed that the dynamic pressure rise in a-C coated

section is not due e-cloud in the coated parts

e-cloud measurement campaign• e-cloud direct and indirect observables have been measured

under different beam conditions for the validation models and codes and as a reference for after LS1

ATS-Note in publication

Summary and conclusions

Electron cloud effects in the PS

• Up to now e-cloud in the PS has never been a limitation for the production of the 25 ns LHC type beams but transverse instabilities are observed when “storing” 25 ns beams at 26 GeV (new transverse feedback helps)

• Double bunch rotation, 10% less voltage during the last bunch splitting, and possibly shorter bunch trains give a significant reduction on the e-cloud activity

• To predict the e-cloud behavior at higher intensities PyECLOUD modules have been developed for the simulation of combined function magnets

• A main magnet will be equipped for e-cloud detection during LS1

Summary and conclusions

Electron cloud effects in the SPS

• No visible effect of electron cloud on nominal LHC 25ns (beam parameters within LHC design report specifications)

• Transverse emittance blow-up on the tail of the bunch train observed during tests with higher intensity

• “Doublet” beam has been tested as a possible scrubbing beam with very encouraging results

• a-C coating have been validated as e-cloud suppression technique in case scrubbing does not work

• e-cloud related measurements have been collected under different beam conditions, to be used for the validation of our e-cloud model and as a reference after LS1

Thank you for your attention!

Possible mitigation strategies: RF voltage program

Together with the RF experts, we tried to optimize the 40MHz voltage program in order to mitigate the e-cloud without affecting the beam quality

0 10 20 30 40 50 60

50

150

250

300

200

100

40 M

Hz R

F Vo

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Time [ms]

Double splitting

b.l.≈14 ns

4 ns

1.25e11 ppb

Double bunch rotation

H. Damerau, S. Hancock, T. Kroyer, E. Mahner and M. Schokker, Electron Cloud Mitigation by Fast Bunch Compression in the CERN PS (No. CERN-AB-2008-050).

Tested in 2008 with encouraging results on e-cloud signals