6.2.2007 Beijing ILC Workshop Global Design Effort 1

High-Gradient Module Test

Lutz Lilje

6.2.2007 Beijing ILC Workshop Global Design Effort 2

Thanks!

• To D. Kostin, Rolf Lange, R. Paparella, K. Przygoda for the viewgraphs

• Many other people involved e.g. DESY technical groups etc.

• Dislaimer:– Some testing still on-going– Final evaluation after 10th cryo-cycle

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Module Test at DESY

• A high gradient module has been assembled

• Test in dedicated test stand underway e.g.– Thermal cycles– Heat loads– Cavity

performance– Coupler

conditioning– Fast tuner

performance

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Overall Module Performance

• Thermal cycling– 10 cycles total planned

• 7 done so far

– No leaks– Wire position o.k.

• Heat loads– Statical heat loads as other modules tested in

TTF/FLASH

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Wire Positions

• Preliminary• Plot illustrates that

positions are repeatably achieved

• Final evaluation to follow

• Also on-going vibration measurements

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Cavity Performance (courtesy D. Kostin – DESY)

1 - AC70 2 - AC76 3 - AC81 4 - Z87 5 - Z85 6 - Z92 7 - Z83 8 - Z900

5

10

15

20

25

30

35

40

Module 6

18.01.2007

EA

CC [M

V/m

]

Cavity

Cavity tests: Vertical (CW) Horizontal (10Hz) CMTB (2Hz) FLASH

Average gradient: 28 MV/m

planned

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Q(Eacc)

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HPP on Cavity 5 +6

• For short pulses up to 300 us gradient is high >30 MV/m

• Radiation levels are relatively low• This hints to a thermal quench

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Cavity results• 6 cavities perform very similar to previous tests

– Even up to 35 MV/m pulsed operation• 2 don‘t…

– Even after HPP, limitation likely thermal quench– The reason is NOT understood (yet)!– Suspicious:

• Cavities behave like twins in all tests– Speculations (!!!!!!!):

• Assembly procedures– After the cavity on position 4 an intermediate leak check is

made, and the necessary additional flange assembly and disassembly could lead to contamination

• Coupler 5 had leak in the warm part (see below), exchange needed

– Should not have impact on cavity vacuum.• Both cavities have not seen 120°C bakeout for schedule

reasons– But CHECHIA test was o.k.

6.2.2007 Beijing ILC Workshop Global Design Effort 10

Coupler Processing(courtesy D. Kostin – DESY)

• Done in to steps– 1st set of 4 couplers

• Very tight vacuum interlock thresholts

– 2nd set of 4 couplers• Used ‘relaxed’ vacuum

interlock thresholts

• Very fast processing– Due to improved handling

after pre-processing at LAL Orsay

– Comparable to individual cavity high power test results

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Coupler 5: Leak in Warm Part

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Reconditioning after Repair

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Second Set of Coupler

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Fast Tuner Tests(R.Paparella –INFN, K. Przygoda – Uni. Lodz, L. Lilje DESY)

• Cavities have two piezos installed – sensor-actuator, redundancy

• Technical remark– All measurements with RF feedforward (no feedback)– All detunings refer to the ‘Flat-Top’-region (beam acceleration) of the RF pulse

• Detuning rather similar for all cavities• All cavities (but one) compensated at maximum gradient with simple pulse

– E.g. Cavity 3 at 35 MV/m– Cavity 5 Piezo no mechanical contact at 1,3 GHz

• Known problem: Piezo fixture stiffness for large pre-detuning of cavity– Currently cavities are compressed, thus exerting an extension of the piezo brackets– This will be changed for future cavities, cavities will pull on fixture

» N.B.: All ILC tuner designs use cavity that pull.• ‘Natural’ frequency of Cavity 5 after cooldown is 317 kHz above 1.3 GHz, larger

compression of cavity needed• At 10 kHz above, operational• Further investigation ongoing e.g. effects due to thermal cycling

– Piezo Voltages within margin• Could also use bipolar operation, but not needed

– Delay of piezo can be used to set cavity pre-detuning

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Lorentz Force Detunings in Module 6 cavities

0

100

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700

800

0 5 10 15 20 25 30 35 40

Eacc[MV/m]

Det

un

ing

ove

r F

lat-

To

p [

Hz]

C1C2C3C4C5C6C7C8

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Example: Cavity 3Lorentz Force Detuning

0

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0 5 10 15 20 25 30 35 40

Cavity Gradient [MV/m]

Lore

ntz

Forc

e de

tuni

ng [H

z]

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Cavity 3: Gradient

35 MV/m

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Cavity 3: Phase

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Cavity 3: Detuning

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Maximum Compensation per Cavity

Maximum Lorentz Force detuning compensation results

0

100

200

300

400

500

600

700

cav 1 - 35 MV/m cav 2 - 31 MV/m cav 3 - 35 MV/m cav 4 - 33 MV/m cav 6 - 20 MV/m cav 7 - 30 MV/m cav 8 - 23 MV/m

Det

unin

g ov

er th

e fla

t-top

[Hz]

Piezo OFF

Piezo ON

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Voltage Needed for Compensation

Compensated Detuning vs. Applied Piezo Voltagehalf-sine pulse, 2.5 ms width and 0.6 to 0.64 ms advance from RF pulse

y = 7,594x

R2 = 0,98

0

100

200

300

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700

0 10 20 30 40 50 60 70 80 90 100

Piezo Voltage [V]

Com

pens

ated

det

unin

g [H

z]

CAV 3

Linear (CAV 3)

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Compensated Detuning vs. Delay to RF@25 MV/m

Normalized detuning over the flat-top for vs. piezo pulse delay

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

-7 -6 -5 -4 -3 -2 -1 0 1 2Piezo pulse start time [ms]

No

rma

lize

d a

mp

litu

de

Delay analysison cavity 1

Delay analysison cavity 2

Delay analysison cavity 6

Delay analysison cavity 7

2nd osc.compensationresults1st osc.compensationresults

RF pulse

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Pre-Detuning Change Due to Piezo Pulse Delay

• Can change the cavity pre-detuning of the cavity by changing the delay of the ‘second‘ pulse in the order of 200Hz

• Changes in pre-detuning could be compensated by changing piezo delay instead of using stepper motor– Less motor usage,

increase lifetime

– Correponds to He drifts of a few mbar

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Summary– No leaks, Static heat loads are o.k.– Cavities

• Six cavities show expected performance• Two cavites perform significantly below their individual high power

test results– Not understood (yet)

– Other components work well• Coupler processed quickly

– Improved handling paid off• Fast tuners perform up to 35 MV/m

– One exception: Problem of the fixture understood

– Module test stand is a big asset• Independent tests of FLASH• E.g. Rapid thermal Cycles

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