1. Radiation shield vibration measurement at KAGRA site
Kazuhiro Yamamoto
on behalf of the KAGRA colloaboration
Department of physics, Faculty of Science,
University of Toyama
Gravitational Wave Advanced Detector Workshop
@Reef view hotel, Hamilton island, Queendland, Australia
10 May 2017 1 1 1 1

2. Abstract
Radiation shield vibration in cryostat could contaminate detector output.
We have already measured this vibration before cryostats were installed at KAGRA site.
Here, I will introduce current status of radiation shield vibration measurement at KAGRA site.

3. Contents
Outlines
Measurement at Toshiba
Measurement at KAGRA site
Calculation
Summary

4. 1. Outlines Two unique key features of KAGRA
Cooled mirror to reduce thermal noise
Underground site with small seismic motion
Y end
3km
3km
Y front
X front
X end
Kamioka mine
(Underground site)
Laser
Atotsu
Center
Cooling system can never bring vibration ! 4 4 4 4 4 4 4 4 4

5. Outlines
Main mirror parts
14m
Beam duct

6. Outlines Vibration isolation system at room temperature Cryo duct
Main mirror parts
Vibration isolation system
at room temperature
Cryo duct
in order to terminate
300K radiation
14m
Beam duct
Cryostat with four cryocoolers

7. 1. Outlines Heat links (soft aluminum) are necessary
Stainless steel t=20mm
Diameter 2.4 m
Height ~4.3 m
M ~ 12 ton
Cold Mass:
8K shield ~455 kg
80 K shield ~590 kg
Seismic Attenuation System (SAS)
Cryogenic Payload
4.3 m
Sapphire Mirror
(-alumina crystal)
View Ports
Radiation Shields
Duct Shield
Main Laser Beam
Cryocoolers
Pulse tube, 60Hz
0.9 W at 4K (2nd)
36 W at 50K (1st)
Four Cryocooler Units
2.6m
Heat links (soft aluminum) are necessary
to cool down cryo payload
S.Koike

8. 1. Outlines
KAGRA adopts pulse tube cryocooler (developed by us) with small vibration.
T. Tomaru et al., Classical and Quantum Gravity 21 (2004) S1005.
Pulse tube
cryocooler
(Sumitomo
Heavy Industries)
Vibration reduction system 8 8 8 8 8 8 8 8 8

9. 1. Outlines Shield vibration could contaminate detector output.
Vibration via heat links could shake mirror.
Phase of (main beam) light could be fluctuated by scattered light in vibrating shield

10. 2. Measurement at Toshiba
What did we do so far ?
Shield vibration measurement at Toshiba Keihin Product Operations (Yokohama) before cryostats were installed at KAGRA site.
D Chen, L Naticchioni et al., Classical and Quantum Gravity 31 (2014)
Frasconi F, Majorana E, Naticchioni L, Paoletti F and Perciballi M
Meas. Sci. Technol. 25 (2014)
Dan Chen (ICRR at that time) and Luca Naticchioni (Rome) developed and installed horizontal and vertical cryogenic accelerometers, respectively, and measured.

11. 2. Measurement at Toshiba
Dan Chen (ICRR at that time) and Luca Naticchioni (Rome) developed and installed horizontal and vertical cryogenic accelerometers, respectively, and measured.
Dan Chen (horizontal)
Luca Naticchioni (vertical) 11 11 11 11 11 11 11 11 11

12. 2. Measurement at Toshiba
How accelerometer works?
We observed motion of mechanical oscillator. Thanks for servo system, this oscillator follows motion of ground. Feedback signal must be proportional to acceleration of ground.
Sensors
Luca (vertical) : LVDT
Dan (horizontal) : Michelson interferometer 12 12 12 12 12 12 12 12 12

13. 2. Measurement at Toshiba
Result at Toshiba
Shield vibration could contaminate detector output.
Vibration via heat links could shake mirror.
Phase of light could be fluctuated by scattered light in vibrating shield
Dan considered (1) and concluded extra pendulum is necessary.
D. Chen et al., Classical and Quantum Gravity 31(2014) , 13 13 13 13 13 13 13 13 13

14. 3. Measurement at KAGRA site
All cryostats and cryo ducts were assembled at KAGRA site.
What are differences measurement at KAGRA site from measurement at Toshiba ?
(1)Seismic motion at site is much smaller.
(2)We “derived” shield vibration “at KAGRA site” from measurement “at Toshiba”. Now we need not to do so, just measure !
(3)At Toshiba, cryostats were not connected anything, cryo ducts, vacuum pipe for vibration isolation system …
(4)Cryostats were NOT fixed on ground in Toshiba. On the contrary, they are fixed.

15. 3. Measurement at KAGRA site
We also measured vibration of ground at Toshiba. We calculated product of Kamioka mine seismic motion and the ratio of shield vibration to ground vibration.
D. Chen et al., Classical and Quantum Gravity 31(2014) , 15 15 15 15 15 15 15 15 15

16. 3. Measurement at KAGRA site
All cryostats and cryo ducts were assembled at KAGRA site.
What are differences measurement at KAGRA site from measurement at Toshiba ?
(1)Seismic motion at site is much smaller.
(2)We “derived” shield vibration “at KAGRA site” from measurement “at Toshiba”. Now we need not to do so, just measure !
(3)At Toshiba, cryostats were not connected anything, cryo ducts, vacuum pipe for vibration isolation system …
(4)Cryostats were NOT fixed on ground in Toshiba. On the contrary, they are fixed.

17. 3. Measurement at KAGRA site
(2)At Toshiba, cryostats were not connected anything, cryo ducts, vacuum pipe for vibration isolation system …
Duct for vibration Isolation System
has been NOT attached yet
3 km duct has been NOT attached yet
Toshiba

18. 3. Measurement at KAGRA site
Now, vacuum ducts are connected to cryostat.
3 km duct has been NOT attached yet
At KAGRA site

19. 3. Measurement at KAGRA site
All cryostats and cryo ducts were assembled at KAGRA site.
What are differences measurement at KAGRA site from measurement at Toshiba ?
(1)Seismic motion at site is much smaller.
(2)We “derived” shield vibration “at KAGRA site” from measurement “at Toshiba”. Now we need not to do so, just measure !
(3)At Toshiba, cryostats were not connected anything, cryo ducts, vacuum pipe for vibration isolation system …
(4)Cryostats were NOT fixed on ground in Toshiba. On the contrary, they are fixed at site.

20. 3. Measurement at KAGRA site
Mission for measurement at KAGRA site started on spring 2016.
Kazuhiro visited Rome to ask Luca join again (vertical accelerometer). He kindly accepted.
Kazuhiro asked Toshiro Ochi (Fresh graduate student in ICRR) to recover Dan’s horizontal accelerometer.

21. 3. Measurement at KAGRA site
On November 2016, both accelerometers were installed at KAGRA site. 21 21 21 21 21 21 21 21 21

22. 3. Measurement at KAGRA site
On November 2016, both accelerometers were installed at KAGRA site.
Kazuhiro
Yamamoto
Toshiro
Ochi
Luca
Naticchioni
Maurizio
Perciballi
Ettore
Majorana
also came.
We did it ! 22 22 22 22 22 22 22 22 22

23. 3. Measurement at KAGRA site
First cooling test was over (April 2017).
We found some issues and have to fix by second cooling test (summer or autumn 2017).
And calculation and analysis are still in progress …
Here, I show only result from horizontal motion at room temperature (in vacuum). 23 23 23 23 23 23 23 23 23

24. 3. Measurement at KAGRA site
Comparison with measurement at Toshiba
Kamioka_cryocooler on
Toshiba_cryocooler on
Comparison with measurement at Toshiba
The vibration level in the cryostat of Kamioka is about 100 times smaller than the measurement by Toshiba below 10 Hz.
It was lower than the vibration at Toshiba in all frequency bands. 24 24 24 24 24 24 24 24 24

25. Measurement result at site
3. Measurement at KAGRA site
Measurement result at site
2 Hz Vibration of cryocooler
and harmonics
Cryocooler off
Cryocooler on

26. Vibration analysis of vacuum chamber and radiation shield
3. Measurement at KAGRA site
Vibration analysis of vacuum chamber and radiation shield
S. Koike investigated vibration modes of radiation shield and vacuum chamber of cryostat using ANSYS, application software of Finite Element Method.

27. Comparison with structural analysis results (radiation shield)
3. Measurement at KAGRA site
Comparison with structural analysis results (radiation shield)
Consistent radiation shield mode
among eigenvalue analysis
mode
frequency(Hz) 1
20.7 2
23.9 3
24.7 4
24.9 5
30.8 6
38.2 7
42.2 8
45.1 10
51.4 11
51.7 12
61.1 19
83.8
1~4 6
10~11 5 19
7~8 12
KEK Koike-san
Many large peaks of the measurement result are consistent with analysis results of the radiation shield.

28. Comparison with structural analysis results (radiation shield)
3. Measurement at KAGRA site
Comparison with structural analysis results (radiation shield)
Consistent radiation shield mode
mode
frequency(Hz) 1
20.7 2
23.9 3
24.7 4
24.9 5
30.8 6
38.2
Kamioka_cryocooler off
Toshiba_cryocooler off
1~4 5 6
Dan Chen also mentions eigenmode of radiation shield was
observed at Toshiba. (Number of observed is from 1th to 6th modes)

29. Comparison with results in Toshiba(vacuum chamber)1
Calculated Vacuum chamber mode
mode
frequency(Hz) 1
11.0 2
22.2
Kamioka
Toshiba
A large peak of 16 to 18 Hz
We didn’t observe large peak around 11 Hz at KAGRA site, but observed large peak between 16 Hz and 18 Hz.
It could be due to connection of 3 km ducts and cryostat is fixed on ground.

30. 4. Calculation How vibration contaminates output of interferometer ?
(1)Vibration via heat links.
(2)Scattered light
(1)Vibration via heat links
After D. Chen’s evaluation, design of cryo payload was drastically changed. We have to take into account and proceed with calculation.

31. 4. Calculation (2) Scattered light
Recently, Simon Zeidler is investigating.
We need baffle to absorb
scattered light from mirror
surface in order to decrease scattered light noise drastically.
Simon evaluates how much scattered light noise with baffles.
Baffle

32. 5. Calculation Preliminary (2)Scattered light.
Recently, Simon Zeidler is investigating.
Preliminary

33. 4. Calculation Investigation is in progress…
Scattered light noise strongly depends on baffle shape.
Vibration isolation system can decrease this noise but it is not taken into account in this graph.
Investigation is in progress…

34. 5. Summary We measured radiation shield vibration at Toshiba.
Now, we are measuring at KAGRA site.
We observed vibration peaks by cryocoolers, resonant modes of shield and vacuum chambers.
We have plan for second cooling in next half year. We must fix issues.
Noise by heat links and scattered light are being evaluated based on measurement result.

35. ELiTES strongly supported Rome group activity for this mission.

36. Thank you for your attention !

37. 1. Outlines
Result at Toshiba
Measured vibration of shield

38. 1. Outlines Result at Toshiba
They derived noise spectrum by vibration via heat links from measured shield vibration
Horizontal Vertical
We need extra pendulum for heat link vibration isolation.

39. 3. Measurement at KAGRA site
They also measured vibration of ground. They calculated product of Kamioka mine seismic motion and the ratio of shield vibration to ground vibration.
It is crucial that this evaluated spectrum is correct !
Vibration which can not be observed at Toshiba could be an issue at KAGRA site.

40. 3. Shield vibration
Measurement of radiation shield vibration at site to evaluate noise
(1)Heat links transmit vibration
(2)Scattered light reflected by shield
Toshiro Ochi reports.

41. 3. Shield vibration
Toshiro installed accelerometers in X front cryostat without cross pipe.
We would like to repeat measurement
after cross pipe connection because
resonant modes of vacuum chamber
could be changed by this connection.
Probably, next measurement around
summer 2017, in other words,
before laser beam passes through
this cryostat. 2F
Cross pipe
vacuum chamber

42. 6. Near future plan
What must CRY do before next f2f meeting (end of August) ?
At KAGRA site
Cooling test of Y front cryostat
Vibration measurement at X front cryostat
Full hanging test of cryogenic payload
(with “blank” sapphire bulk without coating)
at Y end
At KEK
Cryogenic test of cryo payload and
sapphire suspension part
At University of Toyama
HCB for “blank” bulk without coating and ETM

43. Plan for re-measurement with cross pipe
Currently no cross pipe is installed on the cryostat cryo-accelerometer installed . 2F
Eigenmodes of cryostat with cross pipe could be different from that without the duct.
Vibration measurement and hamming test to invstigate eigenmodes are necessary after cross pipe is connected to cryostat.
We would like to perform the cooling test again.
cross pipe
duct
vacuum chamber
KEK　Hagiwara-san

44. Measurement result at site
cryocooler ２
（to cool radiation shield）
Degree of vacuum
temperature
2 Hz Vibration of cryocooler
and harmonics
large peaks at 16 Hz, 23 Hz
Cryocooler off
Cryocooler on

45. Temperature distribution 2016 Nov.28
4K bar for Shield
4K side
80K side
80K bottom
4K bar for Pay 45 45 45 45 45 45 45 45 45