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Electron Stimulated Desorption of OFE Copper Chiara Pasquino, Politecnico di Milano 9th March 2011, RF Structure Meeting
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]
9th March 2011, RF Structure Meeting
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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!
9th March 2011, RF Structure Meeting
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Dynamic Vacuum studies: theoretical models
Gortel Fully Quantum Mechanical Model
MGR Model
e-
Antoniewicz
e-
9th March 2011, RF Structure Meeting
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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
9th March 2011, RF Structure Meeting
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ESD Experimental Set-Up
A
A
V
V
+15 V
2-3 A
35 KV
9th March 2011, RF Structure Meeting
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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!!!
