26 january 07 trond ramsvik ts / mme dc spark test system for clic

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


Cr

0 100 200 300 400 5000

100

200

300

400

500

600

700

800

900


Mo

0 100 200 300 400 5000

100

200

300

400

500

600

700

800

900

Ebr

eakd

own [

MV

/m]


W

0 10 20 30 40 50 60 70 80 900

100

200

300

400

500

600

700

800

900


Al

0 50 100 150 200 2500

100

200

300

400

500

600

700

800

900


Cu

0 50 100 150 2000

100

200

300

400

500

600

700

800

900

C

Ebr

eakd

own [

MV

/m]


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]


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]


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


0 100 200 300 4000

30

60

90

120

150

180

210

240

Eb

reak

dow

n [

MV

/m]


Milled

0 50 100 150 200 250 300


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


0 10 20 30 40 500

30

60

90

120

150

180

210

240

Eb

reak

dow

n [

MV

/m]


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]


OFE Cu

0 50 100 150 200 250


CuZr

0 50 100 150 200 250


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


0 20 40 60 80 100 1200

100

200

300

400

500

600

0510152025303540455055

Ebr

eakd

own [

MV

/m]



0 20 40 60 80 100 1200

100

200

300

400

500

600

0510152025303540455055


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


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

]


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

]


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

]


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]


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


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

26 january 07 trond ramsvik ts / mme dc spark test system for clic

Documents

breakdown conditioning

higher breakdown fields

conditioning speed

cu materials

gas dominaterelease

ovenimmediate conditioning

edm millingcomparison

edm millingglidcop