1

Electron Cloud in LHC

V. BaglinCERN AT-VAC, Geneva

1. Mecanism and Recipies2. LHC Vacuum Chambers

3. Diagnostics4. Conclusions

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 2

1. Mecanism and Recipies

F. Ruggiero et al., LHC Project Report 188 1998, EPAC 98

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 3

Electron Cloud : the Mecanism

• In modern machine with dense bunches and large positive current : KEK-B, PEP-II, SPS, RICH, LHC …• Emittance growth, gas desorption and heat load in cryogenic machine

S

QP

ElectronsElectrons

• Key parameters :bunch structurevacuum chamber dimmensionsecondary electron yieldphoton electron yieldelectron and photon reflectivities…

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 4

Electron Cloud : the Recipies

• Play with the key parameters• Reduce photoelectron yield (perpendicular vs grazing incidence)• Reduce secondary electron yields (scrubbing, TiZrV coatings, carbon coatings, geometry ..)• Reduce the amount of electrons in the system (solenoid magnetic field, clearing electrodes, material reflectivities …)• Adapt the bunch structure or the chamber geometry to reduce multiplication• …

Secondary Electron Yield

N. Hilleret et al., LHC Project Report 433 2000, EPAC 00

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 5

2. LHC Vacuum Chambers

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 6

LHC Dipole Vacuum System• Cold bore (CB) at 1.9 K which ensures leak tightness• Beam screen (BS) at 5-20 K which intercepts thermal loads and acts as a screen

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 7

LHC Dipole Vacuum System

• Rely on scrubbing at cryogenic temperature• With dense bunch current : kick for high energy electrons ! • But large bunch distances to avoid multiplication : 50 to 75 ns or more

O. Gröbner. PAC 1997

Courtesy R. Cimino

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 8

Room Temperature Vacuum System

• ~ 1 μm thick, Non Evaporable Getter TiZrV coated vacuum chambers ensure the required vacuum performances for LHC• Some vacuum chambers were constructed and getter coated …

Courtesy R.Veness AT/VAC and P. Chiggiato TS-MME

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 9

Room Temperature Vacuum System

• ….. and installed inside the LHC tunnel

Warm magnets

Collimators

Vacuum chambers

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 10

TiZrV Vacuum Performances

Courtesy P. Chiggiato TS/MME

10-3

10-2

10-1

100

101

10-7 10-6 10-5 10-4 10-3

1013 1014 1015 1016

Pu

mp

ing

Sp

ee

d

[

s-1 c

m-2]

CO surface coverage [Torr cm2]

[molecules cm-2]

N2

H2

CO

Pumping Speed

PSD Yields

V. Anashin et al. EPAC 2002

Secondary Electron Yield

C. Scheuerlein et al. Appl.Surf.Sci 172(2001)

ESD Yields

C. Benvenuti et al. J.Vac.Sci.Technol A 16(1) 1998

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 11

Room Temperature Vacuum System : Demonstration

Ultimate Vacuum Pressure Distribution after NEG Activation of theLHC Room Temparture Vacuum Sectors

G. Bregliozzi et al. EPAC’08, Genoa 2008

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008 12

3. Diagnostics

13

Vacuum Gauges

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

Courtesy J.M. Jimenez

14

Vacuum Gauges

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

Courtesy J.M. Jimenez

15

Current measurements

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008Courtesy J.M. Jimenez

16

Current measurements

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

Courtesy J.M. Jimenez

17

Current measurements

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

Courtesy J.M. Laurent

18Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

T_uph - T_downh m Q HeHe

T_up T_down

Flowmeter

mHeater

T_BS

Q.

.

COLDEX #101- Scrubbing run 2004 - part 2 - 21 June 2004 13:00-16:0025 ns - BS = 12 K, CB = 3 K - Intensity scan

4 batches

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.00E+00 2.00E+10 4.00E+10 6.00E+10 8.00E+10 1.00E+11 1.20E+11 1.40E+11

Bunch current (protons/bunch)

BS

hea

t lo

ad (

W/m

)

above electron cloud threshold

V. Baglin. APC, 26/5/2005

Heat Load Measurements

19

Heat Load Measurements

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

20

Pilot Sectors

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

• Under definition ..

G. Bregliozzi et al. EPAC’08, Genoa 2008

21

4. Conclusions

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

22

• After repair of sector 3-4 …..

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

23

• And successfull operation with beam …..

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

24

• Followed by …

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

… P. Higgs in the CCC

HIGGS BOSON DISCOVERY

25

• Electron Cloud could show up !

Vincent Baglin Electron Cloud Mitigation Workshop ECM’08- 20/21 November 2008

We are waiting for it !

Meanwhile we (continue) to prepare ourselves