Carbon for SPS, state or the art and scrubbing runs

, P.Chiggiato, P.Costa Pinto, P.Cruikshank, J.Ferreira Somoza, H.Neupert, A.Sapountzis, M.Taborelli, M.Van Gompel, C. Yin Vallgren

Thanks to H.Bartosik, J.Bauche, P.Catherine, K. Cornelis, G.Iadarola, B. Goddard, G.Rumolo, E. Shaposhnikova,

Information expected from scrubbing runs:

- Restarting ECM (e-cloud monitor) with carbon coating after LS1 long venting: any e-cloud due to aging?

- Installation of 2 coated cells: static and dynamic pressure?

- In situ SEY measurement: follow conditioning

What we know and learned on carbon coatings :

On surface and lab :

It was demonstrated that carbon coatings are robust with respect to venting:

-no important increase of SEY in 1 year storage in the lab

-no peel-off issues (scotch tape test) -no dust issue (was addressed in 2008)

Coating of magnets: We can coat single SPS MBB and MBA (hollow cathode)

with a carbon thin film having SEY of 1+/-0.1 (chambers cleaned with detergent)

We can coat QD, QF chambers and re-weld the end flange after assembly, without loss of performance (chambers cleaned with detergent) We can remove the coating with an O2 plasma

Learned after LS1 and during scrubbing 2014

2 carbon coated cells installed (16 dipoles, 4 quads) in LS1: -no static pressure issue upon re-starting after LS1 -dynamic pressure with LHC beam in the same range as other cells

of the ring: dominated by SSS since there is no pressure rise with the doublet beam (doublet makes no e-cloud in SSS) withContribution of quads cannot be excluded

dynamic

coated

drift

uncoated

3e-7

3e-8

3e-9

Static

1e-8

1e-9

Gauge positionP

[mba

r]

P [m

bar]

doublet

5 batches 26GeV 25 ns

Time

In drift sections the effect against e-cloud was demonstrated (solenoid experiment 2012)

Robustness: - no loss of performance of carbon in the e-cloud monitors of SPS after 1 year venting (LS1) and more; ECM in SPS since 2008-coated mobile sample and other samples in SPS vacuum preserved the SEY when in line of sight of the beam

Learned from the 2 cells installation:

Re-installing the magnets needs training- improve transport care to avoid damages - anticipate problems of misalignments on re-assembling (bellows,

RF- shields…); the magnets are not perfectly identical (chamber length, bellows…)

-lowest measured SEYmax of StSt from: 1.38 measured on dark stripe of quad RF-shield (after air exposure)

-lowest measured SEYmax of StSt on mobile sample: 1.6

-trials in the lab (e-gun and multipacting): to go below 1.3 a relevant amount of graphitic C must be present on the surface. The mechanism of this carbon growth is still unclear

-it was not possible to speed up conditioning by feeding C2H2 or C12H26 in the multipacting system

- Lowest SEYmax acheived in multipacting bench (meas. after venting): 1.25

-follow up in next scrubbing runs of the in situ system (drift space)

About conditioning of StSt

Future: Baseline for coating

-dipoles: remove all, detergent cleaning, coating on surface-quadrupoles:

-remove all chambers, coat them on surface, re-weld all in the tunnel

OR -remove all chambers, prepare new coated ones, re-weld all in the tunnelOR- prepare only coated QD chambers and coat QF chambers on

surface, re-weld in the tunnel-RF shields: coated separately or in the dipole or not coated (=3% of cell)-no coating on SSS (=6% of the cell length); other regions in the ring?-option: plasma vs wet cleaning (from “in situ development”)

To do in practice:- Find space for prototype bench- Pilot bench to coat 2 piled-up dipoles to be designed and built- Find space for final workshop on surface, estimate resources: goal is to

do 24 dipoles/week + 5-6 quads/week (744 MB +216 Q)- Issues of interference with RF-upgrade, internal dump…to be checked- Synergy with flange shielding and exchange for impedance reasons to be

checked

In situ option

-dipoles: coat 2 MBA+2 MBB, without displacing them, cleaning with O2 plasma; effectiveness of plasma cleaning with actual state of

chambers and coating with 13m cathode to be tested-quadrupoles:

-remove quads to access the dipoles: move all in one (lose survey reference) or remove one every second one (impact on dipole

coating rate, pumping twice the same 2+2)- same coating options as “baseline” or w’shop in cavern

-RF shields: coating of some separately? For sure not coated between MBA-MBB (0.6% of cell/connection)-no coating on SSS (=6% of the cell length); other regions?

To do in practice:- Find space for prototype bench of 2+2 magnets. - Modular cathodes (train) and anodes to clean/coat 2+2 dipoles to be designed and built- Same as baseline: Issues of interference with

RF-upgrade, dump…to be checked, synergy with flange shielding and exchange for impedance reasons to be checked

Upgrade for hollow C-cathode system

Modular design:

Individual pieces of max. 2 meters

Monoblock cathode

Train-like connection

Special attention to easy mounting and dismounting

Robust (non-ceramic) parts to minimize part failure during installation

All pieces ordered or being fabricated to build mock-up

2m length

Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4

space for the coating bench prototype

design of piled up bench, find space to

test it

construction of piled up system

define cleaning wet vs plasma: if wet,

procure the parts

test cleaning on piled up bench

test coating in piled up bench on MBB

test coating in piled up bench on MBA

order graphite for all cathodes?

order all power supplies?

define strategy for QD, QF

order new chambers for quads QD?

2015 2016

define necessary space, personnel, resrouces for the coating of All SPS in LS2

Planning of developments needed for the baseline

Resources est.

proto bench design

Proto construction

define cleaning

test cleaning on bench

Resources estimate

2 MBA coating in bench 2 MBB

Coating in bench order all

power supplies, cathodes

Strategy for Qs

order QDs chambers?

space for proto-bench

design modular cathodes build 6m cathodes

Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4

space for the coating bench prototype

design of piled up bench, find space to

test it

construction of piled up system

define cleaning wet vs plasma: if wet,

procure the parts

test cleaning on piled up bench

test coating in piled up bench on MBB

test coating in piled up bench on MBA

order graphite for all cathodes?

order all power supplies?

define strategy for QD, QF

order new chambers for quads QD?

2015 2016

define necessary space, personnel, resrouces for the coating of All SPS in LS2

Design modularcathodes

Design anodes

build cathodes 13 m

build anodes 13 m

Building for 4 dipolestest

Install 2 dipoles in 181

Cleaning/coating test

Install 2+2 dipoles

Test on 2+2dipoles

Planning of developments needed for “in situ” option

Thank you for your attention!