Breakdown Study on the CLIC

Designed T18 X-band Structure

Faya Wang

Jul.-31-2008

Topics

• T18 RF Conditioning History

• Breakdown Study on T18

• Summary

CumulatedPhase Change

T18 Structure Profile

120°

FieldAmplitude

The structure is designed by CERN, built at KEK, assembled and bonded in SLAC and tested at SLAC (NLCTA).

Freq.: GHz 11.424

Cells 18+input+output

Filling Time: ns 36

Length: cm 29

Iris Dia. a/λ(%) 15.5~10.1

Group Velocity: vg/c (%) 2.61-1.02

S11/ S21 0.035/0.8

Phase Advace Per Cell 2π/3

Power Needed <Ea>=100MV/m 55.5MW

Unloaded Ea(out)/Ea(in) 1.55

Es/Ea 2

Pulse Heating ΔT: K (75.4MW@200ns) 16.9-23.8

High Power Test Time: hrs 1400

Total Breakdwon Events 2148

Max average Unloaded Gradient at different pulse width:

120MV/m at 70ns for 6hrs (*152MV/m)

120MV/m at 100ns for 76hrs (*152MV/m)

120MV/m at 140ns for 47hrs (*152MV/m)

110MV/m at 190ns for 41hrs (*140MV/m)

120MV/m at 200ns for 21hrs (*152MV/m)

120MV/m at 210ns for 24hrs (*152MV/m)

110MV/m at 230ns for 78hrs (*140MV/m)

~1400 hours total conditioning from 14 Apr. 2008 to 3-Jul-2008

~2148 breakdowns (average 119 per cell)

*:Max accelerator gradient in the structure

RF Conditioning Statistics

RF

Con

ditio

ning

Tim

e: h

rs

1400

60

0

T18VG2.4_Disk structure RF process history begin at Apr.14 2008

The gradient is the average unloaded gradient for the full structure.

The BKD Rate is normalized to the structure length(29cm).

The beginning 500hrs, maximum unloaded gradient is 110MV/m

0 100 200 300 400 5000

50

100

150

Time with RF on: hrs

Ave

rage

Unl

oade

d G

radi

ent:

MV

/m

0 100 200 300 400 500-8

-6

-4

-2

log1

0(B

KD

Rat

e): 1

/pul

se/m

100ns 150ns 230ns 100ns150ns50ns 230ns 200ns

500 600 700 800 900 1000 1100 1200 1300 14000

50

100

150

Time with RF on: hrs

Ave

rage

Unl

oade

d G

radi

ent:

MV

/m

500 600 700 800 900 1000 1100 1200 1300 1400-8

-6

-4

-2

log1

0(B

KD

Rat

e): 1

/pul

se/m

100ns 70~210ns210ns 230ns

230ns 210ns 190ns

Short pulse higher gradient

condition

Pulse shape dependence BKD study.

BKD pulse width dependence study

at 110MV/m.

BKD gradient dependence study at

230ns pulse width

The following 900hrs, maximum unloaded gradient is 120MV/m

300 400 500 600 700 800 900 10000

0.2

0.4

0.6

0.8

1

Time: ns

Stru

ctur

e Fi

led

Am

plitu

de: a

rb.u

.

Breakdown Pulse

Normal Pulse

te

Field Decay time: the time for field collapsed to 5% of

normal field level

Field Decay Time for All Recorded 1100 Events

0 50 100 1500

0.02

0.04

0.06

0.08

0.1

0.12

0.14

Filed Decay Time: ns

Nu

mb

er

of B

rea

kdo

wn

Eve

nts

: pe

rce

nt

Field Decay Time of Breakdown

100 150 200 250

10-6

10-5

10-4

RF Flat Top Pulse Width: ns

BK

D R

ate

: 1/p

uls

e/m

Ea=108MV/m, 250hrs

Ea=110MV/m, 900hrs

Ea=108MV/m, 500hrs

RF BKD Rate Gradient Dependence for 230ns Pulse at

Different Conditioning Time

RF BKD Rate Pulse Width Dependence at Different

Conditioning Time

After 900hrs RF condition BKD rate has a gradient dependence ~

and pulse width dependence ~

32G5.5PW

4.2PW

5.5PW

BKD Rate Characteristics at Different Conditioning Time

95 100 105 110 11510

-7

10-6

10-5

10-4

Unloaded Gradient: MV/m

BK

D R

ate

: 1/p

uls

e/m

BKD Rate for 230ns

250hrs

500hrs

1200hrs

900hrs

95 100 105 110 11510

-7

10-6

10-5

10-4

Unloaded Gradient: MV/m

BK

D R

ate

: 1/p

uls

e/m

BKD Rate for 230ns

250hrs

500hrs

1200hrs

900hrs

500 1000 150095

100

105

110

115

Time with RF on: hrs

Gra

die

nt:

MV

/m

Gradient at 2e-6/pulse/m for 230ns pulse

Experiment DataPower Fit

For Constant Breakdown RateUnloaded Gradient at Different Conditioning Time

95 100 105 110 11510

-7

10-6

10-5

10-4

Unloaded Gradient: MV/m

BK

D P

oss

ibili

ty: 1

/pu

lse

/m

BKD Possibility for 230ns

250hrs

500hrs

1400hrs

1200hrs

900hrs

-100 0 100-5

0

5

10

15

20

25

30

35

40

Reflected Phase: Deg

Fill

ing

tim

e fo

r d

iffe

ren

t ce

ll: n

s

The following test after 1200hrs at 110MV/m@230ns

shows BKD rate is very high up to 1.9e-5/pulse/m.

Then, set at 105MV/m@230ns for 140hrs ( 7 BKD Events )

-100 0 100-5

0

5

10

15

20

25

30

35

40

Reflected Phase: DegF

illin

g ti

me

for

diff

ere

nt c

ell:

ns

Red cross—cell position

Blue dot - breakdown position

0 5 10 15 200

10

20

30

40

50

Cell No.

Pe

rce

nt o

f BK

D E

ven

ts

394 BKDs within 0~250hrs193 BKDs within 250~500hrs298 BKDs within 500~750hrs57 BKDs within 750~900hrs74 BKDs within 900~1000hrs34 BKDs within 1000~1200hrs24 BKDs within 1200~1400hrs

BKD Distribution along Structure at Different Stage Based on the Time of RF Signal

0 500 1000 15000

10

20

30

40

50

60

70

80

90

RF Conditioning Time: hrs

Pe

rce

nt o

f BK

D

Cell 1~4Cell 5~10Cell 11~18

Breakdown Distribution along the Structure in Cell Cluster

Pulse heating related to

breakdown study during the

conditioning stage of 600~700hrs

0 500 1000 1500 20000

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Pre pulse

Main pulse

After pulse

SLED output pulse

Pulse Heating BKD Study

16 18 20 22 240

0.2

0.4

0.6

0.8

1

1.2

Step Pulse Heating for the last cell: K

Per

cent

of

Bre

akdo

wn

Pre-Pulse

Main PulseAfter Pulse

16 18 20 22 24 260

2

4

6

8x 10

-5

Pulse heating for the last cell: K

BK

D P

oss

ibili

ty: 1

/pu

lse

/m

No hot cells during this test

Pre pulse gradient of 100ns pulse width

Time: hr BKD Events

BKD Rate

(1/pulse/m)

Single Pulse 19 16 1.3e-5

81MV/m 16 6 5.8e-6

97MV/m 21 8 5.9e-6

111MV/m 20 81 6.3e-5

119MV/m 21 68 5.0e-5

Main pulse is fixed to 119MV/m of 100ns pulse width

t

dt

PT

0

Pulse Heating for a square pulse P(t)

For step pulse case

Number of pulse to damage the surface at certain pulse heating

*

06exp

TT

Un

U is a constant, T0 surface temperature without pulse heating

*V.F.Kovalenko, "Termophysical Processes and ElectrovacuumDevices", Moscow, SOVETSKOE RADIO (1975), pp. 160-193.

0 t1 t20

P1

P2

16 18 20 22 24 260.08

0.085

0.09

0.095

0.1

0.105

0.11

Pulse Heating for last cell: K

1/ln

(1/B

KD

)

Red line: power level

Blue line: pulse heating

Bad Fit

From T18 experiment result:

.~3/1 constP *From pulse heating related damage caused breakdown:

.~2/1 constP

4

32 .~ PconstT

#From pulse heating on thermal fatigue:

#S. V. Kuzikov & M. E. Plotkin,” Theory of Thermal Fatigue Caused by RF Pulsed Heating”, Int J Infrared Milli Waves (2008) 29:298–311

4

12

.~

PconstT

For a constant breakdown rate, we have:

sns 33~

ns3~

heating Pulse :

Power :

widthPulse:

ΔT

P

5.5

32

~

~

G

*V.F.Kovalenko, "Termophysical Processes and ElectrovacuumDevices", Moscow, SOVETSKOE RADIO (1975), pp. 160-193.

Stresses caused by temperature gradient

Probability to break the link among atoms in a lattice

RF Conditioning history in pulse heating scale

0 500 1000 1500 20000

5

10

15

20

25

30

Accumulated Breakdown Events

Pulse heating for the 1st Cell: kPulse heating for the last cell: k

Based on the experience on the NLC/GLC structure H60VG3, which has a pulse heating temperature of 43K at 65MV/m with 400ns pulse[1], it will not damage the surface on the scale of pulse heating of T18.

[1] C. Adolphsen, ‘Normal-Conducting RF Structure Test Facilities and Results’, SLAC–PUB–9906, September 2003.

Summary

T18 has preformed very well during test, with a

quiet low breakdown rate of less than

1e-6/pulse/m at 106 MV/m with 230 ns pulses at

the end of conditioning, which maybe good

enough for a collider at of 100MV/m, however, it

doesn’t yet have all necessary features such as

higher efficiency and wake field damping.