26 January 07
Trond RamsvikTS / MME
DC Spark Test System for CLIC
26 January 07
Outline
• Experimental Setup• Breakdown characteristics of pure metals
– Esat, Energy, Power
• Mechanical surface treatments– Molybdenum: EDM ↔ Rolled– Copper / GlidCop / CuZr: EDM ↔ Milled
• Heat treatments– Results from annealing with e-beam and oven
• Field Stability• Mass Spectroscopy Studies• Knowledge obtained from DC spark tests • Further plans
26 January 07
Experimental SetupSphere / Plane geometry
HV supply
0 to + 12 kV
UHV
Sample
Tip
A-meter
Field Emission Measurements
HV supply
0 to + 12 kV
UHV
Sample
Tip
Q-meter
Scope
CSwitch
Breakdown MeasurementsSwitch
26 January 07
Typical Conditioning Curves - Scaled
0 100 200 300 4000
100
200
300
400
500
600
700
800
900
Number of Breakdowns
Ti
0 100 200 300 4000
100
200
300
400
500
600
700
800
900
Number of Breakdowns
Cr
0 100 200 300 400 5000
100
200
300
400
500
600
700
800
900
Number of Breakdowns
Mo
0 100 200 300 400 5000
100
200
300
400
500
600
700
800
900
Ebr
eakd
own [
MV
/m]
Number of Breakdowns
W
0 10 20 30 40 50 60 70 80 900
100
200
300
400
500
600
700
800
900
Number of Breakdowns
Al
0 50 100 150 200 2500
100
200
300
400
500
600
700
800
900
Number of Breakdowns
Cu
0 50 100 150 2000
100
200
300
400
500
600
700
800
900
C
Ebr
eakd
own [
MV
/m]
Number of Breakdowns
26 January 07
Electrode Material
Esat EnergyMaterial
Displacement
[MV/m] [mJ]
Graphite 83 3 66 10 < 13 %
OFE Copper 151 39 319 82 < 24 %
Aluminium 155 12 336 26 < 37 %
Tungsten 318 65 775 167 < 37 %
Molybdenum
431 ± 32 854 201 < 10 %1
Chromium 468 26 940 168 < 32 %
Titanium 776 118 1749 212 < 50 %
Saturated Breakdown Fields and Energies
1Valid for non-heated Molybdenum
Perry Wilson:
26 January 07
Saturated Breakdown Fields and Energies
C Cu Al W Mo Cr Ti0
200
400
600
800
1000
1200
1400
1600
1800
En
ergy
[m
J]Elements
C Cu Al W Mo Cr Ti0
100
200
300
400
500
600
700
800
900
Esa
t [M
V/m
]
Elements
HDS 11 Ti
CTF3, HDS 11 Ti:
At ~ 75 ns, energy: ~2700-3000 mJ
DC sparks, Ti:
Energy: ~1500-2000 mJ
26 January 07
Power Flow (Scaled)
C Cu Al W Mo Cr Ti0
5
10
15
20
25
30
Pow
er [
MW
] -
scal
ed
Elements
RF HDS TiPmax = 50 MW @ 40
nsRF circular Mo:
Pmax = 65 MW @ 70 ns
DC:1 mm in diameter => ~0.79 mm2
RF circular Cu:Pmax = 40 MW @ 40
ns
RF:circumference x width = 16 mm2
P = PDC x(16/0.79)
Lower power flow available in the
discharge compared to RF
26 January 07
Chromium
0 75 150 225 300 375 4500
100
200
300
400
500
600
700
800
Eb
reak
dow
n [
MV
/m]
Number of Breakdowns
dgap = 16.7 μm → 14.4 μm
14 % decrease
Esat = (491 11) MV/m
Intensive breakdown conditioning of chromium
shows:• equal and higher
breakdown fields than Molybdenum
• less erosion than Titanium.
26 January 07
Breakdown ConditionsIn addition to the type of electrode materials, the breakdown
characteristics in vacuum for a given field depend on several other important parameters:
• Electrode Geometry and Gap Distance: • Electrode Surface “Finishing” Treatment:
• standard metallurgical polishing techniques
• mechanical • chemical • electrochemical
• heat treatment
• Conditioning Processes:
• removal of contamination and surface smoothing
• field emission
• repeated breakdown events
• Residual gas pressure:
26 January 07
Molybdenum : EDM ↔Cold Rolled
Mo
Rolled / Chem. cleaned
Mo
EDM
0 100 200 300 4000
100
200
300
400
500
600
Eb
reak
dow
n [M
V/m
]
Number of Breakdowns0 300 600 900 1200
0
100
200
300
400
500
600
Eb
reak
dow
n [
MV
/m]
Number of Breakdowns
26 January 07
CuZr : EDM ↔Milling
0 25 50 75 1000
30
60
90
120
150
180
210
240
Esat
= (121 2) MV/mEsat
= (125 4) MV/m
Esat
= (113 1) MV/mEsat
= (142 7) MV/m
EDM
Eb
reak
dow
n [
MV
/m]
Number of Breakdowns0 50 100 150 200 250
EDM
Number of Breakdowns
0 100 200 300 4000
30
60
90
120
150
180
210
240
Eb
reak
dow
n [
MV
/m]
Number of Breakdowns
Milled
0 50 100 150 200 250 300
Number of Breakdowns
Milled
26 January 07
Glidcop : EDM ↔Milling
0 50 100 150 200 2500
30
60
90
120
150
180
210
240 Esat
= (119 ) MV/m
Esat
= (115 3) MV/m
Esat
= (112 ) MV/m
EDM
Eb
reak
dow
n [
MV
/m]
Number of Breakdowns0 50 100 150 200 250
EDM
Number of Breakdowns
0 10 20 30 40 500
30
60
90
120
150
180
210
240
Eb
reak
dow
n [
MV
/m]
Number of Breakdowns
Milled
0 75 150 225 300 375 450Number of Breakdowns
Milled
26 January 07
Comparison: Cu – CuZr - GlidCop
MaterialUNS C
ChemicalComposition
Density
Melt.
Point
ConductivityTemperstate
TensileStrengt
h
Fatigue Strengt
h (ultras. tests)
Supplier
S†
L†† Electr. Therm.at 109
cycles
Mg/m3 Kμ-1cm-1
(IACS%)Wm-1∙K-
1 MPa MPa
Cu-OFE(C10100
)
Cu > 99.99%O2 < 5 ppm 8.94
1356 1356
0.59(101%)
391cold
worked 50%
240-280 120Luvata
Oy
GlidCop® Al-15
(C15715)
Cu = 99.85 %Al2O3 = 0.15 % 8.90
1356 1356
0.54(90%)
365
hot extruded, (no cold working)
393 180
SCM Metal
Products Inc.
CuZr (C15000
)
Cu = 99.8-99.9 %
Zr = 0.1-0.2 %8.89
1253 1355
0.54(93%)
367
aged and cold
worked 40%
340 190Hitachi Cable Corp.
†Solidus ††Liquidus
240-280
393
340
120
180
190
26 January 07
Comparison: Cu – CuZr - GlidCop
0 50 100 150 200 2500
25
50
75
100
125
150
175
200
225
250
275
Ebr
eakd
own [
MV
/m]
Number of Breakdowns
OFE Cu
0 50 100 150 200 250
Number of Breakdowns
CuZr
0 50 100 150 200 250
Number of Breakdowns
GlidCop
Esat = (142 2) MV/m Esat = (121 2) MV/m Esat = (115 3) MV/m
26 January 07
Possible implications for CLIC
the breakdown characteristics are similar for all three Cu materials
the choice of mechanical surface finishing techniques are important to shorten the breakdown conditioning time.
EDM: ~50 and ~200 breakdown events for CuZr and GlidCop, respectively.
Milling: Immediate conditioning for both Cu materials more extreme differences between EDM treated and rolled Mo electrodes
a final decision of cavity materials should be based on other parameters such as from the on-going fatigue measurements.
26 January 07
Mo - heated with e-beam
0 20 40 60 80 100 120 140 1600
100
200
300
400
500
600
Ebr
eakd
own [
MV
/m]
Number of Sparks
Conditioning almost immediately to ~450 MV/m
~ 4 hours in air between heating and mounting in spark system
26 January 07
Mo – heated in oven
0 20 40 60 80 100 1200
100
200
300
400
500
600
T = RT
Ebr
eakd
own [
MV
/m]
0 20 40 60 80 100 1200
100
200
300
400
500
600
0510152025303540455055
T = 1200oC for 2 hours
Number of Breakdowns
0 20 40 60 80 100 1200
100
200
300
400
500
600
0510152025303540455055
Ebr
eakd
own [
MV
/m]
Number of Breakdowns
T = 1000oC for 2 hours
0 20 40 60 80 100 1200
100
200
300
400
500
600
0510152025303540455055
T = 875oC for 2 hours
Immediate
conditioning not
observed
Faster conditioni
ng
No clear improveme
nt in the conditionin
g speed with
increasing temperatur
es
257 252
184 174
recrystallized
26 January 07
0 100 200 300 400 500 6000
50
100
150
200
250
300
350
400
450
500497
473450
429
Ebr
eak o
r E
op [
MV
/m]
Number of Runs
406
Esat
= (422 ± 9)
Field Stability of Conditioned Mo
1 1 29 4 60
1000oC for 2 h
26 January 07
Field Stability of Conditioned Mo
0
100
200
300
400
500
Per
c. B
reak
dow
ns
[%]
Ebr
eak o
r E
op [
MV
/m]
Number of Runs
20
30
40
50
0 100 200 300 400 5000
10
20
30
40
50 xc = 432.2 ± 7.4
Cou
nts
Ebreakd
[MV/m]
0
100
200
300
400
500
35 breakdown events
47 runs
453480
~2900~130
0 ~5600
26 January 07
Mass Spectroscopy
Goal:To provide quantitative information about gas releases during breakdown events.
Provide necessary input parameters for future pressure distribution calculations within the PETS system and the accelerating structure
Pedro Costa-Pinto
26 January 07
Gas Releases - Mo
2700 2750 2800 2850 2900 29504,0x10-10
4,1x10-10
4,2x10-10
4,3x10-10
4,4x10-10
4,5x10-10
4,6x10-10
Ion
Cur
rent
[A
]
Relative Time [sec]
0 500 1000 1500 2700 2800 2900 30000
1x10-9
2x10-9
3x10-9
4x10-9
5x10-9
6x10-9
7x10-9
8x10-9
2,0x10-8
4,0x10-8
6,0x10-8
8,0x10-8
1,0x10-7
1,2x10-7
Pre
ssur
e H
2 [m
bar]
389,341 MV/m
372,037 MV/m
341,755 MV/mIon
Cur
rent
[A
]
Relative Time [sec]
Hydrogen Gas
Example: Release of Hydrogen GasPumping Speed: ~0.3 Litre/sec
26 January 07
Gas Releases - Mo
Releases of H2 and CO gas dominate
Release of gas due to breakdown events
2 4 6 8 10 12 14 16 180.0
2.0x1011
4.0x1011
6.0x1011
8.0x1011
1.0x1012
1.2x1012
1.4x1012 NCO
=(7.4 ± 0.11010*(Pressure Rise - 1)
Num
ber
of C
O M
olec
ules
Pressure Rise
H2O Ar CO2 CH4 CO H2109
1010
1011
# of
Mol
ecul
es /
Uni
t P
ress
ure
Ris
e
Gas
Correlation Pressure Rise <->
Number of Molecules
Number of Molecules per unit pressure rise
Releases of H2 and CO gas dominate
26 January 07
0 100 200 300 400 500 6000
100200300400500
Ebr
eakd
[M
V/m
]
Number of Breakdowns
1
10
100
Ppe
ak/P
bkg
200 300 400 500
4
8
12
16
20
24
28
Pre
ssu
re R
ise
Ebreakdown
[MV/m]
200 300 400 5000
2x1010
4x1010
6x1010
8x1010
1x1011CO
2
# of
CO
2 Mol
ecu
les
Ebreakdown
[MV/m]
200 300 400 5000
3x1011
6x1011
9x1011
1x1012 H2
# of
H2 M
olec
ule
s
Ebreakdown
[MV/m]200 300 400 500
0
3x1011
6x1011
9x1011
1x1012 CO
# of
CO
Mol
ecu
les
Ebreakdown
[MV/m]
Gas releases - Mo
Low Density
High Density
Less energy needed to release
H2
26 January 07
Gas releases – heat treated Mo
0 20 40 60 80
100
200
300
400
500
Eb
reak
dow
n [M
V/m
]
Number of Breakdowns
1
10
100
Pre
ssu
re R
ise
0 100 200 300 400 5000
5
10
15
20
25
30
35
Pre
ssu
re R
ise
Ebreakdown
[MV/m]
Current limiting resistor removed -> Egap = 1/2∙Cdis
∙ U2
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.60
5
10
15
20
25
30
35
Pre
ssu
re R
ise
Energy over Gap [J]
0 20 40 60 80
100
200
300
400
500
Eb
reak
dow
n [M
V/m
]
Number of Breakdowns
1
10
100
Pre
ssu
re R
ise
Low Density
An increase in the energy over the gap causes more gas releases
26 January 07
Gas Experiments – Air/Mo
A B
0 200 400 6000
100
200
300
400
500
600
Number of Sparks
10-910-810-710-6
0 200 400 600 800 1000 1200 1400 16000
100
200
300
400
500
600
Ebr
eakd
own [
MV
/m]
Number of Sparks
10-910-810-710-6
Pre
ssur
e [m
bar] Laboratory
Air
26 January 07
X-ray Photo Emission Spectroscopy
B
238 236 234 232 230 228 2260
10k
20k
30k
40k
50k
60k
70k
80k
90k
MoVI+
5/2MoVI+
3/2
III
II
Inte
nsi
ty [
a.u
.]Binding Energy [eV]
Mo0
3/2
Mo0
5/2
I
MoIV+
3/2
238 236 234 232 230 228 226
0
5k
10k
15k
20k
25k
30k
35k
40k
45k
50k
55k
60k
65kMoIV+
3/2Mo0
3/2
Inte
nsi
ty [
a.u
.]
Binding Energy [eV]
Mo0
5/2
A
0 100 200 300 400 500 600 7000
100
200
300
400
500
600
Eb
reak
d [
MV
/m]
Number of Breakdowns
10-9
10-8
10-7
10-6
P [
mb
ar]
240 236 232 228
Mo0
3/2Mo0
5/2MoVI+
5/2MoVI+
3/2
Binding Energy [eV]
Inte
nsit
y [a
.u.]
Reference Mo
240 236 232 228
Binding Energy [eV]
Inte
nsit
y [a
.u.]
MoVI+
3/2MoVI+
5/2Mo0
3/2Mo0
5/2
240 236 232 228
Binding Energy [eV]
Inte
nsit
y [a
.u.]
MoVI+
3/2MoVI+
5/2Mo0
3/2Mo0
5/2
Breakdown conditioning in UHV removes OxidesBreakdown conditioning in O2 ambience
causes a net formation of oxide film -> influences Esat
26 January 07
Summary - Gas Experiments
Metal
Esat at
p 10-9 mbar(UHV)
Relative decrease in Esat by increasing the gas
pressure to 10-5 mbar
Air CO H2 Ar
MV/m % % % %
Cu 164 ± 30 0 0not
measured
notmeasure
d
W 313 ± 47 30 0not
measured
notmeasure
d
Mo 438 ± 32 35-50 30 0 0
Cr 491 ± ?? 0not
measurednot
measured
notmeasure
d
Ti 697 ± ??not
measured
0not
measured0
26 January 07
Knowledge obtained from DC spark tests
the ranking of breakdown fields in RF and DC experiments is similar for high breakdown rates
the saturated breakdown fields vary with up to one order of magnitude among the studies electrode materials
the effort in finding the optimum material must continue
alloys?
the breakdown conditioning speed can be drastically improved by correct choice of pre-treatments
surface finishing technigues (milling, EDM, ...)
heat treatments (e-beam ↔ oven)
breakdown rate experiments seem to give similar results in RF and DC
Should be given more importance in future studies
for molybdenum and tungsten the vacuum quality influences the ultimate breakdown fields
26 January 07
Future Plans
• Finish the construction of the new spark system:– Two systems running in parallel -> facilitate higher
throughput of materials and preparation techniques – Improvements in the experimental setup
• XYZ movements• E-beam heating → ~ 1000oC
– “In-situ” treatments• several samples• variation of energy over gap more convenient• Upgrade of maximum voltage to ~30 kV
• Dedicate the “old” spark system to breakdown rate experiments– New setup to increase the repetition rate
• Goal ~ 0.5 Hz -> 500’000 runs corresponds to ~12 days
Antoine Descoeudres
26 January 07
Contributors
• Sergio Calatroni
• Ahmed Cherif
• Antoine Descoeudres
• Gonzalo Arnau Izquierdo
• Samuli Heikkinen
• Holger Neupert
• Alessandra Reginelli
• Mauro Taborelli
• Ivo Wevers
• Walter Wuensch
• CLIC Study Team
26 January 07
Automatic Spark Conditioning
Spark Scan Histogram
Molybdenum (Mo) – Tip and Sample
mbar104~atMV/m4398E -8satbreakdown
200 300 400 5000
10
20
30
40
50
Co
un
tsE
breakdown [MV/m]
0 50 100 150 200 2500
100
200
300
400
500
Eb
reak
do
wn
[MV
/m]
Number of Sparks
26 January 07
Depth Profile - Mo
Net Missing Volume:
474914,5 m3
297 m3/spark
~3 ng/spark
@ 0.8 J/spark
26 January 07
Comparison: OFE Cu – CuZr - GlidCop
ElectrodeMaterial:
Enhancementfactor (β):
Esat [MV/m]Elocal [GV/m](average):
√(2σ/e0) [GV/m](average) [2]:
Cu-OFE (465) 57 [1](15139
)170
[1]6.9 9.7 [1] 7.4 - 8.0
CuZr (8623)† (12026)
10.3 9.4
GlidCop® (323)†† (1147) 3.6 8.8
[1] M. Taborelli, M. Kildemo, S. Calatroni, Phys. Rev. ST-AB, 7, 092003 (2004)[2] A. Hassanein, Z. Insepov, J. Norem, A. Moretti, Z. Qian, A. Bross, Y. Torun, R. Rimmer, D. Li, M. Zisman, D. N. Seidman, and K. E. Yoon, Phys. Rev. ST-AB, 9, 062001 (2006)† Milled†† Electro Discharge Machined
26 January 07
Mass Spectroscopy
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09ln(p
t=0/p) =(S
eff/V
tot)*RelTime
B
ln(p
t=0/p
)
Relative Time [sec]
Seff
/Vtot
= 0.026 l/secm3
Seff
~ 0.3 l/sec
10-10 10-9 10-8 10-7
10-8
10-7
10-6
PCO
=1.26Iion
0.87
log10
(PCO
) =0.1+0.9log10
(Iion
)
PC
O [
mb
ar]
Iion
[A]
A
FIG. 2. Calibration to determine the relation between the recorded current from the RGA and the corresponding CO pressure. (A) CO pressure as function of RGA ion current. The open blue squares represent the experimental values. (B) Evolution of the pressure during the first few seconds of a pumpdown of CO. The start pressure was ~5∙10-7 mbar. The measured data is represented by blue open circles. The red line shows the resulting linear fit through the measured points in both figure A and B.
26 January 07
Mass Spectroscopy
t
87.0
i
iion
i
CO20i dt
]A[I
]mol/g[M
sec]/l[S106.1N
0.0
2.0x1011
4.0x1011
6.0x1011
8.0x1011
1.0x1012
1.2x1012
0 2000 4000 6000 8000 10000 12000
0.0
5.0x10-10
1.0x10-9
1.5x10-9
2.0x10-9
2.5x10-9
Pre
ss
ure
(m
ba
r)
Relative Time (sec)
H2
Nu
mb
er o
f M
olec
ule
s
26 January 07
Field Stability of Conditioned Mo
0
100
200
300
400
500
Per
c. B
reak
dow
ns
[%]
Ebr
eak o
r E
op [
MV
/m]
Number of Runs
20
30
40
50
0 100 200 300 400 5000
10
20
30
40
50 xc = 432.2 ± 7.4
Cou
nts
Ebreakd
[MV/m]
500x5000
x