Some thoughts on the evolution of LHC scrubbing

G. Rumolo, G. Iadarola, H. Bartosik

2

10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5x 1014

Time [h]

Tota

l int

ensi

ty [p

]

10 20 30 40 50 60 70 80

0

20

40

60

Time [h]

Hea

t loa

d [W

/hc]

→ After injection and transverse damper set up, 3.5 days of 25ns beam at 450 GeV (6 – 9 December, 2012)

→ Fast intensity ramp up: only one fill with trains of 72 bunches, then trains of 288 bunches

→ Several fills with maximum number of bunches (2748) Very good efficiency Injection time limited by vacuum in the MKI (beginning), then by time required by cryo

to re-adjust to the increasing heat load

Record intensity: 2.7 x 1014 p

Beam 1 Beam 2

3

10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5x 1014

Time [h]

Tota

l int

ensi

ty [p

]

10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5x 10-13

Time [h]

HL/

I [W

/(hc

p)]

Beam 1 Beam 2

Normalized heat load in Sector 5 – 6

→ Scrubbing progress from heat load Clear improvement during the first 60 – 70 hours Slow-down of the process in the last part of the scrubbing

4

→ Beam quality evolution Overview on lifetimes during scrubbing Also from the lifetimes, after a clear improvement at the

beginning, the process seems to significantly slow down

5

10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5x 1014

Time [h]

Tota

l int

ensi

ty [p

]

10 20 30 40 50 60 70 801.35

1.4

1.45

1.5

1.55

1.6

Time [h]

SEY

max

→ Reconstructing the SEY evolution during the scrubbing run Starting from an initial value of 1.55, the dmax in the arc dipoles

seems to quickly flatten at a value slightly below 1.45 Unexpected leveling of the process

From heat load measurements and PyECLOUD simulations

Vacuum evolution (I)• Significant improvement seen in the vacuum (pressure gauges used for

the SEY analysis in the LSS).

Thanks to O. Dominguez, V. Baglin

• Clearer trend in terms of normalized pressure(pressure gauges used for the SEY analysis in the LSS).

Thanks to O. Dominguez, V. Baglin

Vacuum evolution (II)

8

0 5 10 15 20 25 30 35 40 45 500

2

4

6

8

Time [h]

Inte

n. [p

x10

13],

Ener

gy [T

eV]

0 5 10 15 20 25 30 35 40 45 50

0

20

40

60

Time [h]

Hea

t loa

d [W

/hc]

84b

156b 372b

804b804b

→ Heat load in the arcs when ramping up the energy Enhanced heat load probably due to photoelectrons (804 bunches at 4 TeV

produce the same heat load as 2748 bunches at 450 GeV) Violent transient during the ramp (limit of the # of bunches) Not much additional scrubbing visible …

Thanks to L. Tavian

9

→ Beam quality evolution Between the test ramps at 4 TeV and the physics run, there were three more

fills at 450 GeV (14 – 15 December, 2012) Heat load as high as in previous fills with 2748 bunches Emittance degradation still present with 288b fills

170 180 190 200 210 220 2300

5

10

15

20

Time [h]

Inte

n. [p

x10

13],

Ener

gy [T

eV]

170 180 190 200 210 220 230

0

20

40

60

Time [h]

Hea

t loa

d [W

/hc]

170 180 190 200 210 220 2300

5

10

15

20

Time [h]

Inte

n. [p

x10

13],

Ener

gy [T

eV]

170 180 190 200 210 220 230

0

20

40

60

Time [h]

Hea

t loa

d [W

/hc]

Fill 3437: four trains of 288b + one of 144b

Thanks to T. Rijoff, H. Maury-Cuna

10

• Electron cloud in the arcs elsewhere than in the dipoles?→ Quadrupoles, multipoles

• Modeling of the SEY curve → What happens at low energies?→ Re-diffused electrons

• Scrubbing on cold surfaces behaves differently than scrubbing on warm surfaces→ The COLDEX experience

11

• Electron cloud in the arcs elsewhere than in the dipoles?→ Quadrupoles, multipoles

• Modeling of the SEY curve → What happens at low energies?→ Re-diffused electrons

• Scrubbing on cold surfaces behaves differently than scrubbing on warm surfaces→ The COLDEX experience

12

1 1.5 2 2.510

-4

10-2

100

102

104

SEY

Hea

t loa

d [W

/hc/

beam

]

DipoleQuadrupoleDrift

→ Possible interpretation Cells composed of 80% dipoles, but also 6% quadrupole + 14% drift & multipoles SEY thresholds are different in dipole/drift (1.45) or quadrupole (1.2) Electron cloud in dipoles is dominant (1-2 orders of magnitude) as long as dmax >

1.5 in dipole chambers But now quadrupoles (and multipoles?) could be dominant …

→ This could explain Saturation of scrubbing process (scrubbing curve

becomes very steep for SEY below 1.3) Long memory between trains Horizontal blow up

13

• Electron cloud in the arcs elsewhere than in the dipoles?→ Quadrupoles, multipoles

• Modeling of the SEY curve → What happens at low energies?→ Re-diffused electrons

• Scrubbing on cold surfaces behaves differently than scrubbing on warm surfaces→ The COLDEX experience

14

ELECTRON CLOUD STUDIES AND BEAM SCRUBBING EFFECT IN THE SPSJ.M. Jimenez, G. Arduini, P. Collier, G. Ferioli, B. Henrist, N. Hilleret, L. Jensen, J-M. Laurent, K. Weiss, F. Zimmermannhttps://cds.cern.ch/record/615159?ln=it

The Effect of Gas Ion Bombardment on the Secondary Electron Yield of TiN, TiCN and TiZrV Coatings For Suppressing Collective Electron Effects in Storage RingsF. Le Pimpec, R.E. Kirby F.K. King and M. Pivihttps://cds.cern.ch/record/924733?ln=it

15

THE SECONDARY ELECTRON YIELD OF TECHNICAL MATERIALS AND ITS VARIATION WITH SURFACE TREATMENTSV. Baglin, J. Bojko1, O. Gröbner, B. Henrist, N. Hilleret, C. Scheuerlein and M. Taborellihttps://cds.cern.ch/record/466534?ln=it

16

THE SECONDARY ELECTRON YIELD OF TECHNICAL MATERIALS AND ITS VARIATION WITH SURFACE TREATMENTSV. Baglin, J. Bojko1, O. Gröbner, B. Henrist, N. Hilleret, C. Scheuerlein and M. Taborellihttps://cds.cern.ch/record/466534?ln=it

MEASUREMENTS AT EPA OF VACUUM AND ELECTRON-CLOUD RELATED EFFECTSV. Baglin, I. R. Collins, O. Gröbner, C. Grunhagel, B. Henrist, N. Hilleret and B. JenningerChamonix XI

170 50 100 150 200 250 300 3500

0.5

1

1.5

2

Energy [eV]

SEY

0 20 400

0.5

1

1.5

Energy [eV]

SEY

R=1

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THE CHEMICAL ORIGIN OF SEY AT TECHNICAL SURFACESR. Larciprete, D. R. Grosso, M. Commisso, R. Flammini, R. CiminoProceedings of ECLOUD12

19

UsualCosFlat

20

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.810

-6

10-4

10-2

100

102

SEY

Scru

bbin

g do

se (5

0eV)

[mA

/m]

72bpi - cos low en.288bpi - cos low en.72bpi - usual mod.288bpi - usual mod.

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.810

-4

10-3

10-2

10-1

100

101

102

SEY

Scru

bbin

g do

se (5

0eV)

[mA

/m]

72bpi - flat low. en.288bpi - flat low. en.72bpi - usual mod.288bpi - usual mod.

21

• Electron cloud in the arcs elsewhere than in the dipoles?→ Quadrupoles, multipoles

• Modeling of the SEY curve → What happens at low energies?→ Re-diffused electrons

• Scrubbing on cold surfaces behaves differently than scrubbing on warm surfaces→ The COLDEX experience

22

Ep

qsecondaries

elastically reflected

rediffused

23

Re-diffused electrons are not included in our models…

⇒ Re-diffused electrons enhance the build up⇒ Can impact up to a factor 2 on heat load

calculations (e.g. LHC, PS2)

With re-diffused, POSINST model (G. Bellodi, 2004, ISIS studies)

No re-diffused (present model)

⇒ In the present ECLOUD/PyECLOUD model, electrons are either reflected or cause secondary emission

24

Effect of re-diffused electrons: LHC heat load simulations (M. Furman)

25

• Electron cloud in the arcs elsewhere than in the dipoles?→ Quadrupoles, multipoles

• Modeling of the SEY curve → What happens at low energies?→ Re-diffused electrons

• Scrubbing on cold surfaces behaves differently than scrubbing on warm surfaces→ The COLDEX experience

26

ELECTRON CLOUD AND BEAM SCRUBBING IN THE LHCN. Hilleret, O. Bruning, F. Caspers, I.R. Collins, O. Grobner, B. Henrist, J.-M. Laurent, M. Morvillo, M. Pivi, F. Ruggiero, X. Zhang

27

MEASUREMENTS AT EPA OF VACUUM AND ELECTRON-CLOUD RELATED EFFECTSV. Baglin, I. R. Collins, O. Gröbner, C. Grunhagel, B. Henrist, N. Hilleret and B. JenningerChamonix XI

THE SECONDARY ELECTRON YIELD OF TECHNICAL MATERIALS AND ITS VARIATION WITH SURFACE TREATMENTSN. Hilleret , V. Baglin, J. Bojko, O. Gröbner, B. Henrist, C. Scheuerlein, M. TaborelliLHC Project Report 433 (2000)

28

R. Cimino, A surface study on the origin of SEY reduction on accelerator walls, in Electron Cloud Simulations Meeting,29/07/2011

Dose [C/mm2]

10-8 10-6 10-4 10-2 1001

1.2

1.4

1.6

1.8

2

SEY m

ax

Dose [C/mm2]

Scrubbing of Cu measured

with e- at 500eV

C. Yin Vallgren, Ph.D. thesis, CERN-THESIS-2011-063(2011)

29

THE CHEMICAL ORIGIN OF SEY AT TECHNICAL SURFACESR. Larciprete, D. R. Grosso, M. Commisso, R. Flammini, R. CiminoProceedings of ECLOUD12

30

In general (Cu on StSt):

1. E > 100 eV2. About 10-2 C/mm2

dmax below or about 1.2 Scrubbing curve flattens for doses above

10-3 C/mm2 (dmax below 1.3)

Measurements of scrubbing on warm surfaces

31

THE LATEST NEWS ON ELECTRON CLOUD AND VACUUM EFFECTS J.M. JIMENEZ, on behalf of the AT Department/Vacuum Group Chamonix XIII

32

Latest results from COLDEX V. BaglinAPC, 16/05/2005