1. Performance test of KAGRA cryostat at site
Kazuhiro Yamamoto
on behalf of Nobuhiro Kimura
Institute for Cosmic Ray Research (ICRR)
the University of Tokyo
High Energy Accelerator Research Organization
ELiTES: 5th general meeting　　　
University of Toyama, Toyama, Toyama, Japan
10 February 2017 1 1 1 1

2. 0. Abstract
We conducted cooling test before we installed KAGRA cryostat at KAGRA site.
Now cooling test is in progress at site. Progress in last one year is reported here.

3. Contents
Introduction
Before installation at site
After installation at site
Lessons
Summary

4. 1. Introduction Two unique key features of KAGRA
Cooled mirror to reduce thermal noise
Underground site with small seismic motion
3km
Y end
3km
X end
Kamioka mine
(Underground site)
Laser
Atotsu
Center
Cooling system cool down cryostat within short time and temperature must be enough low. 4 4 4 4 4 4 4 4 4

5. Outlines of cryostat Vibration isolation system at room temperature
Main mirror parts
Vibration isolation system
at room temperature
14m
Beam duct
Cooled sapphire mirror
Cryostat

6. Outlines of cryostat 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
S.Koike

7. 2. Before installation at site
Toshiba Keihin Product Operations (Yokohama) fabricated four KAGRA cryostats. Before delivery, they conducted cooling test at their factory (2013). 7 7 7 7 7 7 7 7 7

8. 2. Before installation at site
Yusuke Sakakibara (ICRR at that time) conducted experiment.
Y. Sakakibara et al., Classical and Quantum Gravity 31(2014) 8 8 8 8 8 8 8 8 8

9. 3. After installation at site
In fact, all four cryostat have already been installed at KAGRA site (by Feb 2015) !
We repeat same measurement at KAGRA site ! 9 9 9 9 9 9 9 9 9

10. 3. After installation at site
We repeat same measurement at KAGRA site !
This is exactly challenge because ….
At first we must check air leakage.
At Toshisba,, we can check only vacuum chamber of cryostat. 10 10 10 10 10 10 10 10 10

11. 3. After installation at site
Nowadays, vacuum chamber is much larger.
Leak check is more difficult.
Vibration isolation system
at room temperature
14m
Beam duct
Cooled sapphire mirror
Cryostat 11 11 11 11 11 11 11 11 11 11

12. 3. After installation at site
At Toshisba, main radiation shield in cryostat was closed perfectly.
Y. Sakakibara et al., Classical and Quantum Gravity 31(2014) 12 12 12 12 12 12 12 12 12

13. 3. After installation at site
At KAGRA site, main shield must have hole for laser beam.
Yusuke Sakakibara and Torisha developed cryo duct.
Y. Sakakibara et al., Classical and Quantum Gravity 31(2014) 13 13 13 13 13 13 13 13 13

14. 3. After installation at site
At KAGRA site, shield must have hole for laser beam.
Yusuke Sakakibara developed cryo duct.
According to their result, heat through this duct is enough small. But we must check at site after we assembly cryostat and cryo duct. 14 14 14 14 14 14 14 14 14

15. 3. After installation at site
bKAGRA phase I (by March 2018)
Cryogenic Michelson interferometer
First vibration isolation system above cryostat is being installed at Yend.
We started to check cryostats at Y end. Next check is for X end. 15 15 15 15 15 15 15 15 15

16. 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. 16 16 16 16 16 16 16 16 16 16

17. Cooling test (main radiation shield) at X end (2016.Oct.25~Nov.27）
Nov. 9 Filter in water circulation
system for compressor does not work
Oct 25 Operation start
Toshiba
KAGRA site
Nov 14 Compressor with trouble
was replaced
Initial cooling time is comparable with that at Toshiba.

18. Temperature of main cryostat at Yend
@2016 Nov. 28
~95 K at the top of
the 80 K outer shield
15 K at the side of
8 K inner shield
53~58 K
@ 1st cold stage of Cryo-cooler
6.5 & 14.5 K
@ cryo payload line
12.5~15 shield line
6 & 12.5 K
@ cryo payload line
~15 K
@ 8 K shield

19. Temperature of main cryostat at Yend
@2016 Nov. 28
Lowest temperature is higher than that at Toshiba.
Kimura is NEVER surprised because cryostat must have extra heat load through cryo duct.
Kimura’s comment :
Extra heat load seems to be 10W. This result looks comparable with what we expect based on Sakakibara’s result. But we must check more carefully.

20. Temperature distribution 2016 Nov.28
4K bar for Shield
4K side
80K side
80K bottom
4K bar for Pay 20 20 20 20 20 20 20 20 20

21. Cryo duct（2016.Oct.25~Nov.27） at Y end
Oct. 25 : Operation started
Torisha
KAGRA site
Nov 14 Compressor does not work
Initial cooling times is twice time longer than that at Torisha.
Lowest temperature of cryocooler is comparable with
that at Torisha. Extra heat load ?

22. Temperature distribution 2016 Nov. 28
TBRT-4=112.8 K
TARM-4=82.6 K
Contact to crycooler
(Unexpected contact
to vacuum chamber ?)
TBRT-3=108.1 K
TARM-3=81.0 K
TBRT-2=94.9 K
TARM-2=75.0 K
TBRT-1=85.0 K
TARM-1=70.0 K
We found larger temperature gradient in cryo duct outside main Fabry-Perot cavity (BRT) than that inside cavity ARM). We must check other cryo ducts.

23. Temperature distribution in 80 K cryocooler 2016Nov.28
TBRT-1=48.3 K
TARM-1=43.5 K
Vibration reduction system
TBRT-3=67.6 K
TARM-3=56.3 K
TBRT-2=58.3 K
TARM-2=59.8 K
5N Al heat conductor
We found larger temperature gradient in cryo duct outside main Fabry-Perot cavity (BRT) than that inside cavity ARM). We must check other cryo ducts.

24. 3. After installation at site
Kimura’s comment :
There is not super insulator between main radiation shield and cryo duct. It could be an issue.

25. 3. After installation at site
Plan for other cryostat
X end : Test started on 7th of February ! Cooling down will be finished around 21st of February.
X front : Cooling test will start on 27th of February. Cooling down will be finished around 6th of March.
Y front : Cooling test is coming soon.

26. 4. Lessons How to fix troubles
Large dusts in filter of water circulation system
for compressor of cryocooler,
Compressor suddenly stopped …
How to monitor in long term operation
Monitoring system must be established.
Moreover, somebody checks at site
by his/her eyes.

27. 5. Summary Cooling test at Yend
Initial cooling time of main radiation shield is comparable with that at Toshiba. However, we found extra heat (10W). 300K radiation through cryo ducts ?
We also found extra heat load on cryo duct.
Unexpected contact to vacuum chamber ?
Cooling test of other cryostats started or will start soon.
Lessons: how to fix troubles
how to monitor in long operation