1 X-band Single Cell and T18_SLAC_2 Test Results at NLCTA Faya Wang Chris Adolphsen Jul-9-2009.

1

X-band Single Cell and T18_SLAC_2

Test Results at NLCTA

Faya Wang

Chris Adolphsen

Jul-9-2009

2

• Single cell SW structure test result Breakdown with constant gradient but different pulse heating

Breakdown with constant pulse heating but gradient

• 2nd SLAC made T18 test result

3

1C-SW-A3.75-T2.60-Cu6N-KEK structure parametersParameters Unit Value

Frequency GHz 11.427 (Nitrogen, 20 oC)

Cells 1+matching cell + mode launcher

Q (loaded) 4661

Coupling 0.97

Iris Thickness T mm 2.6

Iris Dia. a mm 3.75

Phase Advance Per Cell deg 180

Es/Ea 2.03

Maximum surface electric field for 10 MW

MV/m 398.9

Maximum surface magnetic field for 10 MW

A/m 667978.1

Peak pulse heating for 1 μs pulse with flat field of 100 MV/m

oC 24

from Valery Dolgashev and James Lewandowski

4

RF In

Two 3 dB hybrid

45 dB coupler

Structure

Half cooling jacket

X-band Current Monitor

Small load

Big load

Ion pump

To big load

Ran cooling water through a

quadrupole magnet adjust structure

temperature.

5

0 500 1000 1500 20000

5

10

15

20

25

30

35

Time (ns)

Inp

ut p

ow

er

of s

tru

ctu

re (

arb

.u.)

Pre Pulse After Pulse

Main Pulse

Input RF Pulse Maximized initial pulse to reduce fill time

6

0 10 20 30 40 50 60 70 80 90 1000

20

40

60

80

100

120

140

160

180

200

Time with RF On (hrs)

Unloaded Gradient (MV/m)Dark Current at Breakdown (arb.u.)

Breakdown Rate (hr-1)Flat Top of 100 ns

RF Processing History During First 100 Hours

Detect breakdown from the large (> 0.8 on above scale) current produced

70 500 1000 1500 20000

5

10

15

20

25

30

35

Time (ns)

Po

we

r (a

rb.u

.)

Input PowerReflected Power DataPower Dissipated in Cavity DataReflected Power SimulationPower Dissipated in Cavity Simulation

0 500 1000 1500 20000

10

20

30

40

50

60

70

80

Time (ns)

Ma

xim

um

Su

rfa

ce P

uls

e H

ea

ting

(a

rb.u

.)

RF Power and Heating Measurements and Simulations

I g R g L R C

Pulse Heating

Simulations basedonly on measured input power

8

0 500 1000 1500 20000

5

10

15

20

25

30

Time (ns)

Ca

vity

Inp

ut P

ow

er

(arb

.u.)

0 500 1000 1500 20000

5

10

15

20

25

30

Time (ns)

Ca

vity

Re

flect

ed

Po

we

r (a

rb.u

.)

0 500 1000 1500 20000

10

20

30

40

50

60

70

Time (ns)

Pu

lse

He

atin

g (

oC

)

Low Pulse HeatingMiddle Pulse HeatingHigh Pulse Heating

Input Power

Reflected Power

Peak Pulse Heating

Breakdown Study with Constant Gradient but Different Pulse Heating from the Pre-Fill ‘Warm-up’

935 40 45 50 55 60 65

10-1

100

101

102

Peak Pulse Heating ( oC)

Bre

akd

ow

n R

ate

(1

/hr)

135 MV/m151 MV/m

1st Test of 145 MV/m

2nd Test of 145 MV/m

Breakdown Rate for Fixed Gradient

1040 50 60 7010

-2

10-1

100

101

102

Peak Pulse Heating (oC)

Bre

akd

ow

n R

ate

(1

/hr)

85 ns150 ns300 ns200 ns135 MV/m @ 150 ns151 MV/m @ 150 ns

145 MV/m @ 150 ns - 1st

145 MV/m @ 150 ns - 2nd

Comparison of these results with those from a similar structure (same a/ tested at the Klystron Test Lab where the pulse shape was fixed so the gradient varies with pulse heating

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0 500 1000 1500 20000

10

20

30

40

50

Time (ns)

Pu

lse

He

atin

g (o

C)

Breakdown Study with Constant Pulse Heating

0 500 1000 1500 20000

5

10

15

20

25

30

Time (ns)

Inp

ut p

ow

er

(arb

.u.)

High gradientMiddle gradientLow gradient

0 500 1000 1500 20000

2

4

6

8

10

12

14

Time (ns)

Re

flect

ed

po

we

r (a

rb.u

.)

0 500 1000 1500 20000

50

100

150

Time (ns)

Gra

die

nt (

MV

/m)

12

115 120 125 130 135 1400

0.5

1

1.5

2

2.5

3

3.5

4

Flat top gradient (MV/m)

Bre

akd

ow

n r

ate

(1

/hr)

First TestSecond TestThird Test

Flat top gradient for 160 ns.(139/129)^25 =6.5

(139/119)^25 = 48.6

Breakdown Rate for Fixed Peak Pulse Heating

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CumulatedPhase Change

Test Results from Second SLAC T18 Disk Structure

120°

FieldAmplitude

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

140 50 100 150 200 250 3000

20

40

60

80

100

120

BKD Rate (hr-1)Average gradient (MV/m)

50 ns 100 ns 150 ns 200 ns

This time, processed structure by progressively lengthening the pulse at constant gradient (110 MV/m)

1595 100 105 110 115

10-7

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

Comparison of current BDR rate (blue circle) with the rate curves from the First SLAC T18 structure at different processing times

T18_SLAC_2

16-150 -100 -50 0 50 100 150-5

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

sRF Breakdown Locations

Blue dot: T18_SLAC_2 after 250 hrs running

Red square: T18_SLAC_1 after 1200 hrs running

0.5

1

1.5

30

210

60

240

90

270

120

300

150

330

180 0

Reflected Power -vs- Reflected Phase

T18_SLAC_2

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Summary

• Reduce fill time with SLED for SW cavity test

• It is possible to separate pulse heating and gradient with SLED for the same structure.

• T18 is a good structure, however it is not clear why there is a hot cell.