1. Cryogenic development in KAGRA
Kazuhiro Yamamoto
on behalf of the KAGRA collaboration
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
We tested performance of KAGRA cooling system (cryostat and so on) before they were installed at KAGRA site.
Here, result of performance test at KAGRA site is introduced.

3. Contents
Outlines
Test before installation at site
Test at KAGRA site
Discussion and 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 4 4 4 4 4 4 4 4 4

5. Outlines
Main mirror parts
14m
Beam duct

6. Outlines We have already installed at site !
Main mirror parts
We have already installed at site !
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 Cryo duct Mirror
Baffle to terminate radiation propagation effectively

9. 1. Outlines
Here, Kazuhiro Yamamoto explains cryostat and cryo duct performance check
(and vibration of shield at site in his next talk).
Cryostat includes most important parts, cryogenic payload with sapphire mirrors.
Takafumi Ushiba shows details of cryogenic payload in next talk.
Koki Okutomi presents control system of vibration isolation system with cryo payload in tomorrow morning session.

10. 1. Outlines KAGRA schedule bKAGRA phase I (until March 2018) :
Cryogenic Michelson interferometer
bKAGRA phase II (until March 2019) :
Cryogenic Fabry Perot Michelson interferometer
Roughly speaking,
Cryostats at both end stations must be ready soon.
Cryostats in center room will be ready in next one year.

11. 2. Test before installation at site
All cryostats and cryo ducts have already been installed at KAGAR site.
Performance test before installation at site
Cryostat : Cooling test of radiation shields
for all four cryostat (Toshiba)
Yusuke Sakakibara et al., Classical and Quantum Gravity 31 (2014)
Cryoduct :
Cooling test for all eight cryo ducts
Measurement of 300K radiation propagation
in cryo duct(Torisha)
Yusuke Sakakibara et al., Classical and Quantum Gravity 32 (2015)

12. 2. Test before installation at site
Result before installation at site
Initial cooling of radiation shield is about two weeks.
This is comparable with our expectation.
After cooling down, temperature is 7 K - 10K.

13. 2. Test before installation at site
Simple evaluation for initial cooling time
KAGRA : Total mass of inner radiation shield
is about 700 kg.
C. Tokoku et al., CEC/ICMC2013, 2EPoE1-03, Anchorage, USA (2013).
Typical specific heat : 1000 J/Kg/K at 300K
Dulong-Petit law
Since power of heat extraction of cryocoolers
is 100 W, the cooling time is 14 days.

14. 2. Test before installation at site
Result before installation at site
Propagation of 300K radiation in cryo duct
Yusuke Sakakibara et al., Classical and Quantum Gravity 32 (2015)
Power transmitted
by cryo duct
Incident power to cryo duct
Cryo duct absorbs 300K radiation enough.

15. 2. Test before installation at site
Then all of cryostats and cryo duct were transported to and assembled at KAGRA site.
KAGRA site
Cryostat
Cryo duct

16. 3. Test at KAGRA site
All cryostats and cryo ducts were assembled at KAGRA site.
Now we are investigating their performance.
What are differences test at KAGRA site from test at Toshiba and Torisha ?
(1)We NEVER checked performance of combined cryostat and cryo ducts.
(2)Radiation shield of cryostat was perfectly closed at Toshiba. Now it is opened (otherwise, laser beam can not achieve mirror !).

17. 3. Test at KAGRA site
Cooling test of cryostats and cyroducts are in progress at site.
Y end
(Done)
3km
3km
Y front
(Not yet)
X front (Done)
X end
(Done)
Atotsu
Center 17 17 17 17 17 17 17 17 17

18. Cooling test (main radiation shield) at X-end (2017.Feb.6~Mar.13）
Feb. 6 Operation start
Toshiba
KAGRA site
Initial cooling time is comparable with that at Toshiba.

19. Temperature of main cryostat at X-end
@2017 Feb. 22
~82 K at the top of
the 80 K outer shield
13.2 K at the side of
8 K inner shield
４７~5６ K
@ 1st cold stage of Cryo-cooler
6.1 & 6.8 K
@ cryo payload system
12.5 shield sysytem
3.9 & 5.7 K
@ cryo payload system
10 & 12 K
@ 8 K shield

20. Temperature of main cryostat at X-front
@2017 Mar. 13
~72 K at the top of
the 80 K outer shield
11.3 K at the side of
8 K inner shield
４2~53 K
@ 1st cold stage of Cryo-cooler
6.0 K
@ cryo payload system
~11.2 shield system
4.3 & 4.5 K
@ cryo payload system
8.4 & 9.6 K
@ 8 K shield

21. Temperature of main cryostat at X-end
@2017 Feb. 22
Lowest temperature is enough low but slightly higher than that at Toshiba.
It could be extra heat load through cryo duct (a few W ?). It looks larger than our expectation.
We are considering what happens exactly ….

22. Result of cooling test of cryo ducts
Bad!
BRT
Y-end-BRT
EYC
Y-end-ARM
KAGRA Cryogenics Configuration
Good!
EYA
3 km
Y-arm
We checked six cryo ducts.
Two of them are OK, but …
IYA ?
Y-front-ARM
IYC ?
Y-front-BS
IXC
EXC
IXA
X-arm
EXA
BRT
Good!
Bad!
3 km
Bad! BS
X-front-BS
X-front-ARM
X-end-ARM
X-end-BRT
Bad!

23. Temperature distribution of the cryo-duct
In case of good result!
TX-BS-4=82.1 K
TY-ARM-4=82.6 K
TX-BS-1=75.9 K
TY-ARM-1=70.0 K
TX-BS-3=81.1 K
TY-ARM-3=81.0 K
TX-BS-2=76.1 K
TY-ARM-2=75.0 K
Upper side: X-front BS side
Lower side: Y-end arm side
We confirmed that two of six cryo-ducts satisfy requirement. One is Y-end arm side, the other one is X-front BS side.

24. Temperature distribution in 80 K cryo-coolers
In case of good result!
TX-BS-1=45.6 K
TY-ARM-1=43.5 K
Vibration reduction system
TX-BS-3=60.6 K
TARM-3=59.8 K
TX-BS-2=53.9 K
TARM-2=56.3 K
5N Al heat conductor

25. Temperature distribution of the cryo-duct
In case of bad result!
TX-ARM-4=96.8 K
TY-BRT-4=112.8 K
Contact to crycooler
(Unexpected contact
to vacuum chamber ?)
TX-ARM-1=90.2 K
TY-BRT-1=85.0 K
TX-ARM-3=96.0 K
TY-BRT-3=108.1 K
TX-ARM-2=90.9 K
TY-BRT-2=94.9 K
Upper side: X-front arm side
Lower side: Y-end BRT side
We found larger temperature gradient in other four cryo-ducts. Now, we are trying to fix of malfunctions
and must check two cryo-ducts at Y-front.

26. Temperature distribution in 80 K cryo-coolers
In case of bad result!
TX-ARM-1=47.9 K
TY-ARM-1=48.3 K
Vibration reduction system
TX-ARM-3=69.1 K
TY-ARM-3=67.6 K
TX-ARM-2=59.7 K
TY-ARM-2=58.3 K
5N Al heat conductor
We found larger temperature gradient in other four cryo-ducts. Now, we are trying to fix of malfunctions
and must check two cryo-ducts at Y-front.

27. 4. Discussion and summary
Initial cooling time at site is comparable with that before installation at site.
We found extra heat load on shield of cryostat and cryo ducts. We have some ideas, but we must check.
We proceed with cooling test at Y front.
However, we expect that they do not matter for bKAGRA phase I. Cryostats and cryo duct can be prepared for phase I !
Nobuhiro Kimura leads installation and check at site. His expertise (cryogenic system in particle accelerators) contribute KAGRA absolutely.

28. Thank you for your attention !

29. 2. Before installation at site
Yusuke Sakakibara (ICRR at that time) conducted experiment.
Y. Sakakibara et al., Classical and Quantum Gravity 31(2014) 29 29 29 29 29 29 29 29 29

30. Pressure after leak test
1. Introduction
X-end Cryostat
7th of Oct 8:47
BRT: 1.9 x 10-4 Pa
EXA: 2.5 x 10-4 Pa
Cryocooler test operation
Y-end Cryostat
BRT: 2.1 x 10-4 Pa、EYA: 2.5 x 10-4 Pa
This pressure is enough low for cooling test. But (small) leakage must be fixed after cooling test, We know where it is and new O-ring has already been ordered. 30 30 30 30 30 30 30 30 30 30

31. Temperature distribution 2016 Nov.28
4K bar for Shield
4K side
80K side
80K bottom
4K bar for Pay 31 31 31 31 31 31 31 31 31