Electron Stimulated Desorption of OFE Copper
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Electron Stimulated Desorption of OFE Copper
Chiara Pasquino, Politecnico di Milano
9th March 2011, RF Structure Meeting
9th March 2011, RF Structure Meeting
2
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
9th March 2011, RF Structure Meeting
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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
9th March 2011, RF Structure Meeting
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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
9th March 2011, RF Structure Meeting
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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
9th March 2011, RF Structure Meeting
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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
9th March 2011, RF Structure Meeting
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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 !!!
9th March 2011, RF Structure Meeting
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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.
9th March 2011, RF Structure Meeting
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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
9th March 2011, RF Structure Meeting
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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
9th March 2011, RF Structure Meeting
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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
9th March 2011, RF Structure Meeting
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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
9th March 2011, RF Structure Meeting
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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.
9th March 2011, RF Structure Meeting
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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!!!
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