High Gradient Performance ofCLIC-Designed Structures

Chris Adolphsen10/12/09

CLIC Quad Structure Tests

In NLCTA Beamline

Structure Note Performance

11/06 – 2/07 C11vg5Q16First X-band Quad

- Irises Slotted Poor: 57 MV/m, 150 ns, 2e-5 BDR –

grew whiskers on cell walls

2/08 - 4/08C11vg5Q16

Redux Refurbished

Initially good (105 MV/m, 50 ns,1e-5 BDR) but one cell degraded

4/07 – 10/07 C11vg5Q16-MoMolybdenum

Version of AbovePoor: 60 MV/m, 70 ns, 1e-6 BDR

10/08 – 12/08 TD18vg2.6_QuadNo Iris Slots but WG

DampingVery Poor: would not process above 50 MV/m, 90ns – gas spike after BD

Test at KEK

08/09 - presentTD18vg2.6_Quad

50 m Rounded Iris Edges

Very Poor: after 400 hours, only reached 60 MV/m with 50 ns pulses

HDX11 X-Band Damped Quad Structure

Number of Cells 11 + 2 Matching

a/ 16 %

Phase per Cell 60 deg

Es/Ea 1.6

vg/c 5.1%

Iris Thickness 1.4 mm

Q 3760

r/Q 13 kOhm/m

For Eacc = 100 MV/m

Input Power 164 MW

Structure Installed in a VacuumCan for Testing

Scattered Dark Spots

Areas of DiscolorationPatchy breakdown areas along sides of irises

Iris Slots

Input Coupler

Iris

Visual/SEM Inspection after Processing

Iris 7&8(Top Right)

Iris 7(Top Right)

After First Run, Decided To

• Electro-polish surface to smooth pits and whiskers

• Fire at 1050 degC (when brazing on water fittings)

to grow large grains

• Attempt to better align quadrants

• Re-install in the can with the orientation reversed

so the ‘good’ end now sees the input power.

Iris 1 Before and After Electro-Polishing

Before Electropolish After 7-minute Electropolish

Before Braze After Braze

After Brazing on New Water Fittings

Quad 7-8: Iris 1. Grain growth significantly increased

0 50 100 150 200 250 300 350 400 4500

20

40

60

80

100

120

Time w ith RF On: hr

C11g5Q16-orignal 07-Nov-2006--18-Dec-2006 23:59:43

Average gradient: MV/m

Pulse w idth: 10nsec

Trip rate: 10/hr

0 50 100 150 200 2500

20

40

60

80

100

120

Time w ith RF On: hr

C11g5Q16-repolished 03-Mar-2008--19-Mar-2008 22:59:33

Average gradient: MV/m

Pulse w idth: 10nsec

Trip rate: 10/hr

0 50 100 150 200 2500

10

20

30

40

50

60

70

Time w ith RF On: hr

C11g5Q16-repolished 03-Mar-2008--19-Mar-2008 22:59:33

Trip rate: /hr

0 50 100 150 200 250 300 350 400 4500

50

100

150

200

250

300

Time w ith RF On: hr

C11g5Q16-repolished 07-Nov-2006--18-Dec-2006 23:59:43

Trip rate: 1/hr

Damaged at100 MV/m, 70 ns

Second RunFirst Run

SEM Photos after Second Run: Nearly all Damage on Sides of Cell 1 in One Quadrant

1 cell 0 cell2 cell3 cell4 cell

5 cell6 cell7 cell8 cell9 cell

Opposing ‘Tips’ on Side Walls

‘Stonehenge’First Iris

above the Damaged Quadrant

Molybdenum HDX11

TD18 Quad Structure

TD18 Quad Processing History

0 5 10 15 20 25 30 35 40 450

50

Ave

rag

e U

nlo

ad

ed

Gra

die

nt:

MV

/m

0 5 10 15 20 25 30 35 40 450

50

100

Time with RF on: hrs

Bre

akd

ow

n R

ate

: 1/h

r

90ns

80ns60ns80ns

Breakdowns Located Throughout Structure

TD18 Quad Post-Run Examination

Not able to take good photos or SEM images, but saw damage similar to CERN 30 GHz HDX-like structures except practically

no pitting on the irises (i.e., all breakdowns near joints)

30 GHz NDS4_vg2.5_thick

30 GHz HDS4_Thick Post Mortem

See similar metal protrusions in the TD Quad structure

Edges rounded (50 micron radius) in TD18 produced at KEK

Recent KEK Results from Testing a TD18 Quad Structure with 50 m Rounded Iris Edges

60 MV/m

Structure a/ (%)P

(MW)

E (MV/m

)

HDS60vg8.0 19 16.1 61

HDS60vg5.1 16 13.3 75

HDS4vg2.6_thick 17.5 7.5 67

NDS4vg2.5_thick 17.5 8.6 75

C30vg4.7 17.5 21.0 94

C40vg7.4_/2 20 19.2 65

C30vg4.7_sb 17.5 20 92

All measured data at 70 ns pulse length and 10-3 breakdown rate

Summary of 30 GHz Structures

Steffen Doebert

In NLCTA Beamline

Structure Note Performance

4/08 – 7/08T18vg2.6-Disk

SLAC_1Cells by KEK,

Assembled at SLAC

Good: 105 MV/m, 230 ns at LC BDR spec of 8e-7/pulse/m but hot cell

developed

7/08 – 10/08T18vg2.6-Disk

SLAC_1Powered from

Downstream EndGood: 163 MV/m, 80 ns, 2e-5 BDR in last cell, consistent with fwd operation

12/08 – 2/09T18vg2.6-Disk

CERN_1CERN Built, Operate

in Vac CanVery Poor: very gassy with soft breakdowns at 60 MV/m, 70 ns

Test at KEK

10/08 – 06/09

T18vg2.6-Disk

KEK_1Cells by KEK,

Assembled at SLACGood: 102 MV/m, 240 ns at LC BDR

spec – no bkd location info

7/09 – 8/09T24vg1.8Disk

CERN_1CERN Built, Cells

Pre-FiredPoor: achieve < 60 MV/m after 100 hours with pulse lengths < 100 ns

5/09 - presentT18vg2.6-Disk

SLAC_2Cells by KEK,

Assembled at SLACGood: after 280 hours, 97 MV/m, 230 ns

at LC DBR spec – one hot cell

CLIC Disk Structure Tests

T18-Disk Structure(First attempt at an optimal CLIC structure)

Field Profile Along the Structure

Cells 18+input+output

Filling Time: ns 36

Length: cm 29

a/λ (%) 15.5 ~ 10.1

vg/c (%) 2.6 - 1.0

S11/ S21 0.035 / 0.8

Phase Advance Per Cell 2/3

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

Unloaded Ea(out)/Ea(in) 1.55

Es/Ea 2

Pulse Heating ΔT: K (75.4MW@200ns)

16.9 - 23.8

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

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

Experiment DataPower Fit

Gradient Increase Over Time at a Constant Breakdown Rate

Hot Cell Flare-up

First T18 StructureTested at SLAC

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 Stages of Processing

Did not find visual evidence related to the hot cell in a post-run boroscope exam – typical of NLC/GLC structures, many of which had hot cells

First T18 StructureTested at KEK

Operated 3900 hours

0 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)

Second T18 Structure Tested at SLAC

95 100 105 110 115

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

-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 LocationsBlue dots: T18_SLAC_2 after 250 hrs running

Red squares: 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

CERN Built T18Cells made by Kugler, no etch, 820 degC vacuum braze at CERN,

installed in a vacuum can at SLAC

Copper grain size small due to ‘low’

braze temperature

Photo of Iris

0 10 20 30 40 50 60 70 80 900

50

100

Ave

rag

e U

nlo

ad

ed

Gra

die

nt: M

V/m

0 10 20 30 40 50 60 70 80 900

50

100 Bre

akd

ow

n R

ate

: 1

/hr70ns 230ns 200ns70ns

CERN T18 Processing History

Time (hr)

Breakdown Characteristics T18_Disk_1 during last 500 hrs, ~ 115 MV/m, 220 ns

T18_Disk_CERN during last 40 hrs, ~ 50 MV/m, 200 ns

-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

0 10 20 300

0.2

0.4

0.6

0.8

1Missing Energy -vs- Breakdown Position (cell #)

-100 0 10010

-2

10-1

100Reflected Power -vs- Reflected Phase (deg)

0 50 100 150 200 250

0

0.2

0.4

0.6

0.8

1Missing Energy -vs- Time of Breakdown (ns)

Time of Breakdown (ns)

Fra

ctio

nal M

issi

ng E

nerg

y

Loca

tion

of B

reak

dow

n (n

s)

Iris 12 Autopsy

A 200 micron long calcium and carbon rich object that appears to have caused surface melting over a 1 mm wide area on this iris

4 6 8 10 12 14

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Position (a.u.)

E fie

ld (

a.u

.)

11.427 GHz FROM INPUT

CERN T24 Disk Structure

Cells 24+input+output

Filling Time: ns 61

Length: cm 30 (wg2wg)23 (24+2 cells)

a/λ (%) 12.6 - 9.4

vg/c (%) 1.8 - 0.9

S11/ S21 0.016 / 0.715

Phase Advance Per Cell 2/3

Power Needed <Ea> = 100 MV/m 42.4 MW

Unloaded Ea(out)/Ea(in) 108/90

Es/Ea 2

Pulse Heating ΔT: K (<100MV/m>@100ns)

7.5 – 8.4

Field Profile Along the Structure

T24 Fabrication• Manufactured

at VDL, Q4 ‘08 • Assembly at CERN with

“new” procedure (following T18 task force ) Apr-Jun 09

• Pre-fire of disks at 1040 ˚C. Resulting uneven surface caused braze leaks

• Cells oxidized at one point but it was removed with 650 ˚C bake

• Now back at CERN for evaluation

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

Time with RF On (hr)

Average Unloaded Gradient (MV/m)BKD Rate (1/hr)

T24 Processing History at 100 ns and Shorter Pulse Lengths

0.2

0.4

0.6

0.8

30

210

60

240

90

270

120

300

150

330

180 0

Reflected Phase -vs- Relfected Power (max)

0 10 20 30 40 50 60-10

0

10

20

30

40

50

Bkd Event Number

BK

D P

ositi

on (

ns)

Breakdown Locations

Summary• With strong dependence on structure fabrication

technique, cannot evaluate performance dependence

on structure geometry (a,vg,phi)

• Quad approach does not appear viable

– Need to improve quad ‘z’ alignment and reduce virtual leaks

– Probably cannot allow irises to touch nor have a low phase advance per cell

(which lowers Es/Ea)

– Should do a final test of a 2/3, brazed version with slots

• T18 design is very promising, but not optimal for CLIC

– Three versions have operated at CLIC-like parameters although they take

> 1000 hours of operation to achieve low breakdown rates

• Future

– CERN adopting SLAC-like structure assembly techniques

– Verify T24 with HOM damping meets CLIC specs (will test TD18_disk first)

LC