Electron Stimulated Desorption of OFE Copper

Chiara Pasquino, Politecnico di Milano

9th March 2011, RF Structure Meeting

9th March 2011, RF Structure Meeting

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Dynamic Vacuum: an issue for CLIC accelerating structures

Static Vacuum: 10-9 mbar [G.Rumolo, C.Garion]

Dynamic Vacuum: CO2, H2 < 10-9 mbar

Technical Note, EDMS 1095288

http://ilcagenda.linearcollider.org

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Dynamic vacuum sources due to the High Gradient

Breakdowns: during the discharge a gas burst is always detected;

Dark Currents: FE currents that don’t lead to a breakdown impinge on the Copper surface causing the ESD Effect.

FAST ION – BEAM INSTABILITIES

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Dynamic Vacuum studies : Breakdowns

2*102 H2 or CO molecules released [exp. Data DC “spark test” reported in PRST-AB12, 092001 (2009)];

Uniform pressure along the structure after ~ 3ms;

Background pressure recovered after 20 ms, no dynamic vacuum problems.

[C.Garion]

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Dynamic Vacuum studies : ESD

e- on faraday cup

e- are uniformly distributed inside the cell

e- on faraday cup

S. Calatroni

Faraday Cup measurement - T18_VG24_Disk_2 – KEK [T. Higo] ESD measurement on unbaked Copper [ N. Hilleret, CAS Vacuum School 2006 - G. Vorlaufer CERN-Thesis (2002)]

H2 PP = 1.12E-8 mbar 10 times higher CO2 PP = 3.37E-9 mbar 3 times higher

NEW ESD EXPERIMENTAL DATA ON UNBAKED OFE COPPER AT HIGH ELECTRON ENERGY NEEDED!

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Dynamic Vacuum studies: theoretical models

Gortel Fully Quantum Mechanical Model

MGR Model

e-

Antoniewicz

e-

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Desorption Yield

VolQ

pumpQ

desQ

Steady State Condition

0**

jjdes

j

vol

j SpVtp

Vtp

jjdes

j SpVtp

*

kTeISpp s

jjjj 01

s

jjjj kTI

eSpp

01

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Sample Campaign

w/o etch

Passivatio

n SLAC etch

w/o etch

Passivatio

nSLAC etch

w/o etch

Passivatio

nSLAC etch

w/o etch

Passivatio

nSLAC etch

w/o etch

Passivatio

nSLAC etch

w/o etch

Passivatio

n SLAC etch

w/o etch

Passivatio

n SLAC etch

w/o etch

Passivatio

nSLAC etch

w/o etch

Passivatio

n SLAC etch

CERN 2 2 2 2 2 2 2 2 2 2 2 2 24

Bodycote 2 2 2 2 2 2 2 2 2 18SLAC 2 2 2 2 2 4 14

2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 4 56

Hydrogen (1 bar)

elliptical samples

Vacuum dynamics REFERENCE Vacuum Argon (mbar) H2 (mbar) H2 (1 bar) Vacuum Argon (mbar) Hydrogen (mbar)

• 3 Cleaning Procedures : w/o etching, passivation & SLAC etching

• Several Thermal Treatment : Vacuum, Argon, H2 atmosphere @ 1040 or 820 °C

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H2 Diffusion Profiles :SLAC bonding

0 100 200 300 400 500 600 7000

300

600

900

1200

2020 20

1040 1040

800

1040_H2

Time (minutes)

T (

°C) H2 H2

Cu – H is an endothermic system! equal Cs at both surfaces

TpHxH

242677.4log21log 2

RTD 37320exp10*34.8 3

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H2 Diffusion Profiles: SLAC bonding

-0.5 0.0 0.51.1993573x10-4

1.1993574x10-4

C (%

wt)

x (cm)

H in Cu, 1h30 @ 1313

-0.5 0.0 0.51.194x10-4

1.196x10-4

1.198x10-4

1.200x10-4

C (%

wt)

x (cm)

1309 K 1305 K 1301 K 1297 K 1293 K 1289 K 1285 K 1281 K 1277 K 1273 K 1269 K

Ramp down, 4K/min

-0.5 0.0 0.51.1782x10-4

1.1784x10-4

1.1786x10-4

1.1788x10-4

C (%

wt)

x (cm)

1073 K

H in Cu @ 1073 K

-0.5 0.0 0.51.40x10-9

1.45x10-9

1.50x10-9

1.55x10-9

1.60x10-9

C (%

wt)

x (cm)

10 d 5 d 2 d 1 d 10 h 8 h

Heat treatment after bonding

THE ANNEALING TIME CAN BE DECREASED !!!

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ESD Experimental Set-Up

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ESD Experimental Set-Up

A

A

V

V

+15 V

2-3 A

35 KV

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Measurement Scheme

~ 20 s of desorption pulse; precise check of the background pressure; train of measurement continuous check of the pressure through the dual gauge read by Labview [thanks Rocio!!]; steady state condition useful experimental data.

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Experimental Data @ 10 KeV: Cu spare samples

1E11 1E12 1E13 1E14 1E15 1E161E-4

1E-3

0.01

0.1

1D

es Y

ield

(#m

ol/e

-)

Dose (e-/cm2)

H2 CH4 H2O N2/CO C2H6 CO2

ESD @ 10 kV

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Experimental Data @ 10 KeV: 19_PCV082C

1E15 1E161E-4

1E-3

0.01

0.1D

es Y

ield

(mol

/e-)

Dose (e-/cm2)

H2 CH4 H2O N2/CO C2H6 CO2

PCV082C @ 10 kV

Experimental Error Analysis 2

2

0

222 0

IPPIPP

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Energy Correlation: Stopping Powers

1E-3 0.01 0.11

10

Stop

ping

Powe

r (M

eV cm

2 /g)

Kinetic energy (MeV)

Stopping Power

Copper

1E-3 0.01 0.1

10

100

Stop

ping

Powe

r (M

eV cm

2/g)

Energy (MeV)

Hydrogen

1E-3 0.01 0.11

10

100

Stop

ping

Powe

r (M

eV cm

2/g)

Energy (MeV)

Nitrogen

1E-3 0.01 0.11

10

100

Stop

ping

Powe

r (M

eV cm

2/g)

Energy (MeV)

CO2

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Energy Correlation: Experimental Data

0 2 4 6 8 10 12 14

1E-3

0.01

0.1

Des

Yie

ld (m

ol/e

-)

Energy (keV)

H2 CH4 H2O N2/CO C2H6 CO2

19_PCV082C

Increase up to 2.5 KeV, then a small decrease; From 5 to 15 KeV, no dependence! Something to be studied in the future!

5 10 15 20

1E-3

0.01

0.1

Des

Yie

ld (m

ol/e

-)

Energy (keV)

H2 CH4 H2O N2/CO C2H6 CO2

19_PCV082C, Dose: 2.7E15

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Conclusions A new experimental set – up has been built in

order to provide ESD experimental data for unbaked copper at higher electron energy, as required;

The experimental set – up has been improved and it’s correctly working;

Further investigations about SLAC procedure are needed;

Further investigations on the energy correlation are required as well.

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THANKS FOR THE ATTENTION!!!!

Many thanks to: Sergio, Mauro, Walter, Rocio, Helga, Jan, Markus, Ivo, Donat, Pawel, Luigi, Paul, Wil, Holger!!!