Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results...

Vacuum, Surfaces & Coatings GroupTechnology Department 04/12/2014

R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN

COLDEX results during SPS Scrubbing Run I

R. Salemme, V. Baglin, G. Bregliozzi

on behalf of TE-VSC group

Electron Cloud Meeting #18

CERN

December 04th 2014



• First COLDEX experimental run during SPS Scrubbing Run I (03-10/11)• COLDEX inserted on Monday 3rd at 12:00: no impact on beam lifetime• COLDEX sector extracted on Monday 10th, at 6:00

Objectives and achievements• Accumulation of beam time and electron dose

→ Time integrated beam current exceeds 4 A∙h→ different, in some cases limited, circulation time before dump (at flat bottom, at flat top)

• Study with different SPS parameters (beams and intensities)→ from 1 to 5 batches of 72 bunches, 25 ns bunch spacing, up to 1.3E+11 ppb→ mainly at 26 GeV/c, but also with acceleration to 450 GeV/c

• Study at 2 beam screen temperatures: ~50 K, then ~5-10 K

• Study with doublet beams (5+20 ns hybrid spacing)→ observed limited effects due to field-free and a-C coated region

COLDEX: SPS Scrubbing Run I

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COLDEX Measurements

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• Total pressures along the vacuum system: VGIs

• Partial pressures in the RT and cryogenic parts: RGAs

• Electron activity on the

middle electrode: chimney biased electrode

• BS and CB temperatures: CERNOXs

• Heat load on the beam screen



Preliminary Results: overview

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50 K

5 K10 K



Preliminary Results: at 50 K

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Preliminary Results: H2 evolution

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Preliminary Results: at 5K

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Preliminary Results: H2 evolution

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Conclusions for Scrubbing Run 1● Within the beam time obtained during the first SPS Scrubbing Run, first

observations of a-C coating at 50 K and 5-10K with LHC type beams and

doublet beams did not reveal strong effects of vacuum degradation imputable to

electron cloud

● Along the scrubbing run, significant pressure rises were observed outside the

COLDEX system, while in COLDEX a pressure rise has been observed mainly

due to H2 gas accumulation at 50 K

● No appreciable electron activity was observed on the RT electron collector of

COLDEX: below 50 nA

● Observed dissipated heat loads along the a-C coated beam screen are smaller

than 1 W/m

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Future perspectives: 2014● Participation to second SPS Scrubbing Run: 08-09-10?/12

→ longer studies with BS at 10 K, CB at 3 K

→ more interested in higher beam intensities rather than doublets (low

effectiveness for COLDEX location and set-up)

(gradually) increase of bunch intensity: > 1.3∙1011 ppb

inject 4 batches or more

→ long beam circulation time before dump is essential

Operate with maximum achievable beam dump time to get cycle close

to 100 %

● Improve understanding of dynamic effects linked to H2

→ in-situ different gas injections and evolution follow-up during Xmas TS

→ simulations

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R. Salemme – COLDEX results during SPS Scrubbing Run I Electron Cloud Meeting #18, CERN 11

Future perspectives: 2015● COLDEX is not compatible with LHC PHYSICS operation (too much time for

extraction/insertion)

● Participation to SPS Scrubbing Runs in 2015. Preliminary schedule sees:

w.16 → but LHC re-commissioning with beam: compatible?

w.22 → depending on LHC Technical Stop 1 (Mo-Fr)

● Perform specific studies e.g. gas accumulation, different BS temperature

ranges, coating ageing, etc. during 2015 MDs

→ ~ 5 x (8-12) hours “fully dedicated” MDs with LHC type beams

→ possible allocation: before LHC operation (February) and close to LHC

TSs?



Future perspectives: 2016● During last IEFC (28/11), L. Rossi approved COLDEX runs also for 2016 (Crab

Cavities will be installed in SPS LSS4 in EYETS 2016-17)



Acknowledgments● Strong support and commitment of many CERN groups for COLDEX

refurbishment and operation: TE-VSC, TE-CRG, BE-OP, BE-ABP, TE-EPC, EN-

ICE

● Thanks to L. Rossi, HL-LHC project leader, Crab Cavities, WP 4, and Cryogenic,

WP9, projects for their support to operate COLDEX during 2016

Vacuum, Surfaces & Coatings Group Technology Department 04/12/2014 R. Salemme – COLDEX results...

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