6.2.2007 Beijing ILC Wor kshop Global Design Effort 1 High-Gradient Module Test Lutz Lilje
Dec 13, 2015
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
6.2.2007 Beijing ILC Workshop Global Design Effort 3
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
6.2.2007 Beijing ILC Workshop Global Design Effort 4
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
6.2.2007 Beijing ILC Workshop Global Design Effort 5
Wire Positions
• Preliminary• Plot illustrates that
positions are repeatably achieved
• Final evaluation to follow
• Also on-going vibration measurements
6.2.2007 Beijing ILC Workshop Global Design Effort 6
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
6.2.2007 Beijing ILC Workshop Global Design Effort 8
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
6.2.2007 Beijing ILC Workshop Global Design Effort 9
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
6.2.2007 Beijing ILC Workshop Global Design Effort 19
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
6.2.2007 Beijing ILC Workshop Global Design Effort 20
Lorentz Force Detunings in Module 6 cavities
0
100
200
300
400
500
600
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
6.2.2007 Beijing ILC Workshop Global Design Effort 21
Example: Cavity 3Lorentz Force Detuning
0
100
200
300
400
500
600
700
800
0 5 10 15 20 25 30 35 40
Cavity Gradient [MV/m]
Lore
ntz
Forc
e de
tuni
ng [H
z]
6.2.2007 Beijing ILC Workshop Global Design Effort 25
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
6.2.2007 Beijing ILC Workshop Global Design Effort 26
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
400
500
600
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)
6.2.2007 Beijing ILC Workshop Global Design Effort 27
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
6.2.2007 Beijing ILC Workshop Global Design Effort 28
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
6.2.2007 Beijing ILC Workshop Global Design Effort 30
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