Breakdown Study on the CLIC Designed T18 X-band Structure and Lband 5-Cell SW Cavity

Breakdown Study on the CLIC

Designed T18 X-band Structure

and Lband 5-Cell SW Cavity

Faya Wang

Jul.-09-2008

Topics

• T18 RF Conditioning History

• BKD study on T18

• Pulse heating study on T18

• L-band cavity RF Conditioning History

• BKD Study on Lband cavity

• Summary

CumulatedPhase Change

Frequency. 11.424GHz

Cells 18+input+output

Filling Time 36ns

a_in/a_out 4.06/2.66 mm

vg_in/vg_out 2.61/1.02 (%c)

S11 0.035

S21 0.8

Phase 120DegAverage Unloaded Gradient

over the full structure55.5MW100MV/m

T18 Structure Profile

5.1~__ inaccoutacc EE

120°

FieldAmplitude

Max average Unloaded Gradient at different pulse width:

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







~1000 hours total conditioning from 14 Apr. 2008 to 26-Jun-2008

~2148 breakdowns (119 per cell)

*:Max accelerator gradient in the structure

RF Conditioning Statistics

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).

0 100 200 300 400 5000

50

100

150

Time with RF on: hrs

Ave

rage

Unl

oade

d G

radi

ent M

V/m

0 100 200 300 400 500-6

-5

-4

-3

log1

0(BK

D R

ate)

: 1/p

ulse

/m

200ns50ns100ns 150ns 230ns 230ns 100ns150ns

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

500 600 700 800 900 1000 1100 1200 1300 14000

50

100

150

Ave

rage

Unl

oade

d G

radi

ent:

MV

/m

500 600 700 800 900 1000 1100 1200 1300 1400-6

-5

-4

-3

Time with RF On: hrs

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

95 100 105 110 11510

-7

10-6

10-5

10-4

BKD Rate for 230ns Pulse

Unloaded Gradient: MV/m

BK

D R

ate:

1/p

ulse

/m

500hrs

900hrs

1200hrs

250hrs

100 150 20010

-7

10-6

10-5

10-4

RF Flat Top Pulse Width: ns

BK

D R

ate:

1/p

ulse

/m

RF BKD Rate Gradient Dependence for 230ns Pulse at

Different Conditioning Time

After 250hrs RF Condition



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

G=108MV/m

G=108MV/m

G=110MV/m

BKD Rate Characteristics at Different Conditioning Time


The Error of Breakdown rate for the last two point at 1200hrs is very large, because it only got few events for a week running.

1000 1200 1400 1600 1800 2000 220095

100

105

110

115

Accumulated Breakdown Events

Gra

die

nt:

MV

/m

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

Experiment results for 2100 BKDs

Power fit for 2100 BKDs: bkd^0.24598

Experiment data at 2100~2150 BKDs

500 1000 150095

100

105

110

115


Gra

die

nt:

MV

/m

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

Experiment results for 1200hrs

Power fit for 1200hrs: t^0.10479Experiment data at 1400hrs

95 100 105 110 11510

-7

10-6

10-5

10-4



BK

D R

ate:

1/p

ulse

/m

500hrs

1200hrs

250hrs 1400hrs

900hrs

95 100 105 110 11510

-7

10-6

10-5

10-4



BK

D R

ate:

1/p

ulse

/m

500hrs

1200hrs

250hrs

900hrs

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

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

the hot cells are dominating the breakdowns.

-100 0 100

0

10

20

30

40

Reflected Phase: Deg

Fill

ing

tim

e fo

r d

iffe

ren

t ce

ll: n

s

-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

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

0 5 10 150

5

10

15

20

25

Cell No.

Pe

rce

nt o

f BK

D E

ven

ts

After 250hrs with 1143 BKDsAfter 500hrs with 1342 BKDsAfter 750hrs with 1825 BKDsAfter 900hrs with 1933 BKDsAfter 1000hrs with 2056 BKDsAfter 1200hrs with 2109 BKDsAfter 1400hrs with 2148 BKDs

BKD Distribution along Structure at Different Stage

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.1

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.2

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.3

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.4

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.5

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.6

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.7

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.8

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.9

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.10

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.11

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.12

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.13

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.14

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.15

0 50010000

10

20

Time: hrs

Per

cent

BK

DCell No.16

0 50010000

10

20

Time: hrsP

erce

nt B

KD

Cell No.17

0 50010000

10

20

Time: hrs

Per

cent

BK

D

Cell No.18

BKD Cell Distribution Evolution with RF Conditioning Time

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.1

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.2

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.3

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.4

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.5

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.6

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.7

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.8

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.9

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.10

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.11

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.12

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.13

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.14

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.15

0 100020000

10

20

BKDs:

Per

cent

BK

DCell No.16

0 100020000

10

20

BKDs: P

erce

nt B

KD

Cell No.17

0 100020000

10

20

BKDs:

Per

cent

BK

D

Cell No.18

BKD Cell Distribution Evolution with Accumulated BKDs

BKD Cell Distribution Evolution with Cell Dissipated Energy

0 500

10

20

Dissipated Pow er: MJ

Per

cent

BK

D

Cell No.1

0 500

10

20


Per

cent

BK

D

Cell No.2

0 500

10

20


Per

cent

BK

D

Cell No.3

0 500

10

20


Per

cent

BK

D

Cell No.4

0 500

10

20


Per

cent

BK

D

Cell No.5

0 500

10

20


Per

cent

BK

D

Cell No.6

0 500

10

20


Per

cent

BK

D

Cell No.7

0 500

10

20


Per

cent

BK

D

Cell No.8

0 500

10

20


Per

cent

BK

DCell No.9

0 500

10

20

Dissipated Pow er: MJP

erce

nt B

KD

Cell No.10

0 500

10

20


Per

cent

BK

D

Cell No.11

0 500

10

20


Per

cent

BK

D

Cell No.12

0 500

10

20


Per

cent

BK

D

Cell No.13

0 500

10

20


Per

cent

BK

D

Cell No.14

0 500

10

20


Per

cent

BK

D

Cell No.15

0 500

10

20


Per

cent

BK

DCell No.16

0 500

10

20


Per

cent

BK

D

Cell No.17

0 500

10

20


Per

cent

BK

D

Cell No.18

Breakdown Cell Distribution at Different Stage

0 5 10 15 200

5

10

15

20

Cell No.

Bre

akd

ow

n E

ven

ts: p

erc

en

t

1~201 Breakdown Events

y(x) = a x^na = 0.070631n = 1.8328R = 0.81556 (lin)

0 5 10 15 200

5

10

15

20

Cell No.

Bre

akd

ow

n E

ven

ts: p

erc

en

t


y(x) = a x^na = 0.72984n = 0.91333R = 0.90839 (lin)

0 5 10 15 200

5

10

15


Cell No.

Bre

akd

ow

n E

ven

ts: p

erc

en

t y(x) = a x^na = 0.21073n = 1.4129R = 0.88267 (lin)

0 5 10 15 200

5

10

15

20

Cell No.

Bre

akd

ow

n E

ven

ts: p

erc

en

t


y(x) = a x^na = 0.37801n = 1.1808R = 0.82287 (lin)

0 5 10 15 200

5

10

15

20

Cell No.

Bre

akd

ow

n E

ven

ts: p

erc

en

t


y(x) = a x^na = 0.40069n = 1.1587R = 0.90972 (lin)

0 5 10 200

5

10

15

20

Cell No.

Bre

akd

ow

n E

ven

ts: p

erc

en

t


y(x) = a x^na = 0.13204n = 1.3354R = 0.87676 (lin)

Breakdown Cell Distribution Dependence decreasing with Conditioning

For the last point the fit is applied without these hot cells (cell # 6~10)

200 400 600 800 1000 12000.8

1

1.2

1.4

1.6

1.8

2

Number of Breakdown Events in Time Sequence

Exp

on

en

t Co

nst

an

t n fo

r P

ow

er

Fit

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 Evolution time: the time for field

collapsed to 5% of normal field level

0 50 100 1500

2

4

6

8

10

12

Filed Evolution Time: ns

Nu

mb

er

of B

rea

kdo

wn

Eve

nts

: pe

rce

nt

Gaussian Fit for All Events

y(x) = a exp( - ((x -x

0)^2) / (2 ^2))

a = 10.722 = 17.845x

0 = 53.904

R = 0.97192 (lin)

Field Evolution Time for All Recorded Breakdown Events

Why there is multi-peak evolution time from data?

0 200 400 600 800 1000 12000

50

100

150

Breakdown Events No. in Time Squence

Fie

ld E

volu

tion

Tim

e: n

s

Field Evolution Time at Different Stage with Gaussian Fit

0 50 100 1500

5

10

15

20

25

30

35

Field Evolution Time: ns

Nu

mbe

r o

f Bre

akd

ow

n E

ven

ts: p

erc

en

t

1-200 Breakdown Events

y(x) = a exp( - ((x -x

0)^2) / (2 ^2))

a = 24.089 = 15.767x

0 = 48.062

R = 0.93224 (lin)

0 50 100 1500

5

10

15

20

25

30

35


Nu

mbe

r o

f Bre

akd

ow

n E

ven

ts: p

erc

en

t


y(x) = a exp( - ((x- x

0)^2) / (2 ^2))

a = 24.024 = 14.482x

0 = 52.214

R = 0.96101 (lin)

0 50 100 1500

5

10

15

20

25

30

35


Nu

mbe

r o

f Bre

akd

ow

n E

ven

ts: p

erc

en

t


y(x) = a exp( - ((x- x

0)^2) / (2 ^2))

a = 19.683 = 19.402x

0 = 56.013

R = 0.94342 (lin)

0 50 100 1500

5

10

15

20

25

30

35


Nu

mb

er o

f Bre

akd

ow

n E

ven

ts: p

erc

en

t


y(x) = a exp( - ((x -x

0)^2) / (2 ^2))

a = 22.856 = 14.868x

0 = 49.875

R = 0.9317 (lin)

0 50 100 1500

5

10

15

20

25

30

35


Nu

mb

er o

f Bre

akd

own

Eve

nts

: pe

rce

nt


y(x) = a exp( - ((x -x

0)^2) / (2 ^2))

a = 21.312 = 17.636x

0 = 53.351

R = 0.97215 (lin)

0 50 100 1500

5

10

15

20

25

30

35


Nu

mb

er o

f Bre

akd

ow

n E

ven

ts: p

erc

en

t


y(x) = a exp( - ((x -x

0)^2) / (2 ^2))

a = 19.816 = 18.009x

0 = 62.17

R = 0.95492 (lin)

200 400 600 800 1000 120040

45

50

55

60

65

Number of Breakdown Events in Time Sequence

Fie

ld E

volu

tion

Tim

e: n

s

Field Evolution Time increasing with Conditioning

Could be dominated by hot cell breakdown

0 500 1000 1500 2000

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Pre pulse width and

average unloaded gradient

Main pulse width and

average unloaded gradient

Time: hr BKD Events BKD Rate

(1/pulse/m)

Single Pulse 100ns@119MV/m (*150MV/m)

19 16 1.3e-5

100ns@81MV/m 100ns@119MV/m (*150MV/m)

16 6 5.8e-6

100ns@97MV/m 100ns@119MV/m (*150MV/m)

21 8 5.9e-6

100ns@111MV/m 100ns@119MV/m (*150MV/m)

20 81 6.3e-5

100ns@119MV/m 100ns@119MV/m (*150MV/m)

21 68 5.0e-5Pre pulse

Main pulse

After pulse

SLED output pulse

*:Max gradient in the structure

15 16 17 18 19 20 21 22

10-5

10-4

Average Pulse Heating for the full structure: K

BK

D R

ate

: 1/p

uls

e/m

15 16 17 18 19 20 21 220

20

40

60

80

100

Average Pulse Heating for the full structure: K

Pe

rcen

t of b

rea

kdo

wn

eve

nts

Pre pulse breakdownMain pulse breakdownAfter pulse breakdown

Pulse Heating BKD Study

2.94 2.96 2.98 3

x 10-3

0

1

2

3

4

5

6x 10

5

1/(T0+ T)

Nu

bm

er

of p

uls

e fo

r b

rea

kdw

on

y(x) = a exp(b x)a = 8.368e-023b = 21305R = 0.47567 (lin)

t

dt

PT

0

Pulse Heating for a square pulse P(t)

12111 222 ttPttPtPT

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

Very bad Fit

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

0 t1 t20

P1

P2

From T18 experiment result:

.~3/1 constP From pulse heating 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

0 200 400 600 800 1000 1200 1400 1600 1800 2000 22000

5

10

15

20

25

30

Accumulated Breakdown Events

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

0 200 400 600 800 1000 1200 14000

5

10

15

20

25

30


Pulse heating for the 1st Cell: kPulse heating for the last cell: kAccumulated breakdown events divided by 10

RF Conditioning history in pulse heating scale

For 230ns square pulse, BKD rate gradient dependence in

Pulse heating scale

20 25 3010

-6

10-5

10-4

Pulse heating for the last cell: K

BK

D R

ate

: 1/p

uls

e/m

500hrs

250hrs

Ea=108MV/m

900hrsEa=110MV/m

Ea=108MV/m

26 27 28 29 30 3110

-7

10-6

10-5

10-4

Pulse heating for the last cell: K

BK

D R

ate

: 1/p

uls

e/m

250hrs

500hrs

1200hrs

1400hrs900hrs

BKD rate pulse width dependence in Pulse

heating scale

L-band Warm conductor 5 cell π mode

SW cavity RF conditioning results

Cold Test Hot Test

Frequency: MHz.

1299.68 1299.679

Cells 5 5

Q0 29000 28642

Phase pi pi

Gradient(1MW): MV/m

7.6MV/m 7.3~7.5

Structure Profile

J. Wang

RF Conditioning Statistics till Jan-4-2008

Pulse Width: us

Conditioning Time: hrs

100 160

200 20

400 70

1000 280

Total 530

(~5.5e6 pulses)

~Max unloaded Acc. Gradient: 15MV/m

~6167 Breakdown Events (1233 per cell)

5Hz repeating frequency

1Hz repeating frequency

0 0.5 1 1.5 2 2.50

2

4

6

8

10

12

14

Power: MW

Gra

die

nt:

MV

/m

100us RF pulse and beam at 85us G=7.34*sqrt(P)

1100us RF pulse and beam at 85us G=7.49*sqrt(P)1100us RF pulse and beam at 900us G=7.23*sqrt(P)

Predict value G=7.6*sqrt(P)

336.2

Gradient SurfacePeak :

a

p

p

EE

E

Cavity unloaded gradient Measurement results

0 5 10 15-30

-25

-20

-15

-10

-5

0

Time: us

dB

m

Reflected Power at BKDStore Energy Decay at BKDNormal Reflected PowerNormal Stored Energy Decay

0 5 10 15 20 25-40

-35

-30

-25

-20

-15

-10

-5

0

Time: us

dB

m


Hard Event Soft Event

KLY WG CavityCIR

0 5 10 15-25

-20

-15

-10

-5

0

Time: us

dBm

Normal OFF Records Index ------ 22-Nov-2007 06:54:17

Input power of Cavity at BKD

Reflected Power of Cavity at BKD

Store Energy Decay at BKDKlY output

Normal Reflected Power

Normal Store Energy Decay

Interesting WG BKD

0 5 10 15-25

-20

-15

-10

-5

0

Time: us

dB

m

Red dash line: normal store energy decay

Red solid line: store energy decay for WG BKD

Blue line: klystron output power

Black solid line: decay curve for cavity at Q0

BKD spot in WG with klystron still on block RF power emitted from Cavity

5Hz 1Hz RF Conditioning History

2.5 2.55 2.6 2.65 2.7 2.75-5

-4

-3

-2

-1

0

1

2

Ln(E): E in MV/m

Bre

ak d

own

rate

: Ln

(B)

1/hr

Ln(B) = 20.7*Ln(E) - 55.9

data 1

linear

PE 6.7

Breakdown rate vs Gradient

For BKD rate pulse width dependence measurement has not been done yet.

21~ G

0 100 200 300 400 500 6000

10

20

30

40

Time: hr

Bre

akdo

wn

rate

: 1/

hr

0 100 200 300 400 500 6000

0.2

0.4

0.6

0.8

1

Time: hr

Hard breakdown rate percent

Soft breakdown rate percent

0 0.5 1 1.5 2 2.5 3 3.5 410

-4

10-3

10-2

10-1

100

Breakdown time interval: hr

Pos

sibi

lity

0~135hrs-5Hz

135~270hrs-5Hz270~405hrs-1Hz

405~528hrs-1Hz

BKD Characteristics with RF conditioning Time

5Hz 1Hz

Map BKD LocationB re akdo wn

D r iving C e ll

R e f le c te d P o we r S to re d E ne rgy D am ping

e e

p ic k-up1 s t Ir is 2 n d Ir is 3 r d Ir is 4 th Ir is

0 5 10 15 20 25-40

-35

-30

-25

-20

-15

-10

-5

0

Time: us

dB

m


0 0.5 1 1.5 2 2.5 3-30

-25

-20

-15

-10

-5

0

5

Time: t/0

Nor

mal

ized

to

Pea

k F

or.

Pow

er:

dB

Field decay with 1st Iris blocked

Normal reflected power

Normal end cell stored energyReflected power with 1st iris blocked

Stored energy with 1st iris blocked

0 0.5 1 1.5 2 2.5 3-30

-25

-20

-15

-10

-5

0

5

Time: t/0

Nor

mal

ized

to

Pea

k F

or.

Pow

er:

dB

Field decay with 2nd Iris blocked


Normal end cell stored energyReflected power with 2nd cell blocked

Stored energy with 2nd cell blocked

0 0.5 1 1.5 2 2.5 3-30

-25

-20

-15

-10

-5

0

5

Time: t/0

Nor

mal

ized

to

Pea

k F

or.

Pow

er:

dB

Field decay with 3rd Iris blocked


Normal end cell stored energyReflected power with 3rd cell blocked

Stored energy with 3rd cell blocked

0 0.5 1 1.5 2 2.5 3-30

-25

-20

-15

-10

-5

0

5

Time: t/0

Nor

mal

ized

to

Pea

k F

or.

Pow

er:

dB

Field decay with 4th Iris blocked


Normal end cell stored energyReflected power with 4th cell blocked

Stored energy with 4th cell blocked

0 5 10 15-30

-25

-20

-15

-10

-5

0

Freq: MHz

Am

plitu

de:

dB

FFT on stored energy no iris blocked

FFT on stored energy with 1st iris blocked

FFT on stored energy with 2nd iris blocked FFT on stored energy with 3rd iris blocked

FFT on stored energy with 4th iris blocked

Beating frequency of stored energy for blocking different iris

Summary - Questions

• Why pulse width dependence changing with RF conditioning time (accumulated BKDs)?

• Why BKD location distribution changing with time?• Why field evolution time becoming longer?• Why hot cells are in the middle of the T18?• Do we reach the gradient limit of T18 (can the hot cells

recovery with further conditioning)?

……• Is L-band cavity processing over?• What does the soft event and hard event mean?

….

T18 Lband Cav.

Type TW SW

Freq. 11.424 1.3

Phase 120 180

BKDs per cell 119 1233BKD~Grad. dependence G^32 G^21

BKD~pulse width dependence PW^5.5 N/A

Pulse Width 230ns 1ms

Unloaded Grad. 100MV/m(55.5MW) 10MV/m (1.8MW)

Repeating Freq. 60Hz 5Hz1Hz

Length 30cm 58cm

Hot Cells (6~10) N/A

Total RF Cond. Time 1400hrs 530hrs

Overall BKD Rate 2.36e-5/pulse/m 1.79e-3/pulse/m

T18 & Lband Cavity Data Summary

Documents

Breakdown Study on the CLIC Designed T18 X-band Structure and Lband 5-Cell SW Cavity