1. Overview of the 20K configuration
Kazuhiro Yamamoto
Institute for Cosmic Ray Research, the University of Tokyo
I will explain cryogenic payload.
23 May 2016
Gravitational Wave Advanced Detector Workshop
@ Hotel Hermitage, La Biodola, Isola d’Elba, Italy 1 1

2. 0. Abstract KAGRA mirror : 20K ET-LF mirror : 10K
(1)How much is the noise below 20K ?
We expect smaller noise.
(2)However, cooling below 20K is challenge.
What are issues ?
I will explain cryogenic payload.

3. Challenges for cooling Summary
Contents
Introduction
Noise vs temperature
Challenges for cooling
Summary
I will explain cryogenic payload.

4. Introduction Motivation : Why the mirrors and suspension are cooled ?
(1)Small thermal noise
(2)Small thermal lens
(3)Less serious parametric instability
(4)Small cosmic ray effect
Kenji Numata and Kazuhiro Yamamoto,
”Chapter 8. Cryogenics”, in ”Optical Coatings and Thermal Noise in Precision
Measurement” Cambridge University Press (2012).
T. Tomaru et al., Classical and Quantum Gravity 19 (2002) 2045.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
K. Yamamoto et al., Journal of Physics: Conference Series 122 (2008)
K. Yamamoto et al., Physical Review D 78 (2008) 4 4 4 4

5. Introduction Room temperature second generation interferometer
Fused silica mirror suspended by fused silica fibers
This suspension is not a good for cryogenics.
Large mechanical dissipation
and low thermal conductivity at low temperature
Other material with small dissipation and high thermal conductivity
Sapphire or Silicon
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 5 5 5 5

6. 2. Noise vs Temperature
Motivation : Why the mirrors and suspension are cooled ?
(1)Small thermal noise
Mirror thermal noise
Substrate thermoelastic, Coating Brownian
Pendulum thermal noise
Wire thermoelastic, Wire Brownian
Kenji Numata and Kazuhiro Yamamoto,
”Chapter 8. Cryogenics”, in ”Optical Coatings and Thermal Noise in Precision
Measurement” Cambridge University Press (2012).
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 6 6 6 6

7. 2. Noise vs Temperature Mirror substrate thermal noise (thermoelastic)
Baseline is 3km. Beam radius is 35mm.
Operation temperature must be below 20 K or around 120 K.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Sensitivity of 2nd generation 7 7 7 7 7 7

8. 2. Noise vs Temperature Coating thermal noise (Brownian)
Coating loss angle is 5*10-4.
Coating thermal noise does not limit sensitivity below 20 K.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Sensitivity of 2nd generation 8 8 8 8 8 8

9. 2. Noise vs Temperature Pendulum thermal noise (Thermoelastic)
Mirror is 23kg.
Thinnest wire
(Wire strength limit)
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Sensitivity of 2nd generation
AdLIGO fiber : 0.4mm
Below 120K, thermoelastic noise does not matter.
A.V. Cumming et al.,
Classical and Quantum Gravity
29 (2012) 9 9 9 9 9 9

10. 2. Noise vs Temperature Pendulum thermal noise (Brownian)
Sensitivity of 2nd generation
T. Uchiyama et al., Physics Letters A 273 (2000) 310 (Sapphire).
Wire Q is 5*106.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Below 120K, Brownian noise dominates but it does not matter. 10 10 10 10 10 10

11. 2. Noise vs Temperature Summary
Any thermal noise is enough small below 20 K.
Especially, thremoelastic noise reduces drastically.
Other kinds of thermal noise is also small because thermal noise formula (Fluctuation-Dissipation Theorem) includes temperature (Power spectrum density is proportional to Temperature). 　
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 11 11 11 11 11 11

12. 3. Challenges for cooling
How to keep temperature with heat load ?
(a) Is cooling power enough large ?
(b) Is heat path enough ?
2. How to cool down as short as possible at initial ?
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 12 12 12 12 12 12

13. 3. Challenges for cooling Sapphire or Silicon fibers
3-1. How to keep temperature with heat load ?
Sapphire or Silicon fibers
Pulse tube cryocoolers
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Absorption in mirror
KAGRA : 1W
ET-LF : 0.1W
Mirror(below 20K) 13 13 13 13 13 13 13 13 13 13 13 13 13

14. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(a)Cooling power of cryocoolers
Y. Sakakibara et al., Classical and Quantum Gravity 31 (2014)
According to KAGRA experiment, power is enough !
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 14 14 14 14 14 14

15. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
Mirror is in vacuum.
Radiation is about 1 mW at most.
Thermal conduction is only solution.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 15 15 15 15 15 15

16. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
Which do we need (crystal or pure metal) ?
Both of them !
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 16 16 16 16 16 16

17. 3. Challenges for cooling Sapphire or Silicon fibers (High Q values)
3-1. How to keep temperature with heat load ?
(b)Heat path
Sapphire or Silicon fibers (High Q values)
Pure metal (Soft)
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Mirror 17 17 17 17 17 17

18. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
8 K
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Intermediate mass
How much is temperature ?
Mirror
10 K - 20 K 18 18 18 18 18 18

19. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
Intermediate mass temprature
Too high : Sapphire fibers must be too thick.
(Large thermal noise)
Too low : Heat links must be too thick.
(Large external vibration)
We must face trade off.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 19 19 19 19 19 19

20. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
Intermediate mass temperature
is close to mirror temperature.
Constant
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. T3 20 20 20 20 20 20

21. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
8 K
Intermediate mass
10K-16K
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Absorption in mirror
0.1W – 1W
Mirror
10K-20 K 21 21 21 21 21 21

22. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
Diameter of sapphire fiber
Size limit : Upper limit of thermal conductivity of fiber, which is proportional to diameter.
T. Tomaru et al., Physics Letters A 301 (2002) 215.
Heat absorption in mirror : 0.1 W - 1 W
Temperature of mirror : 13K-23K
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Here we adopt 1.6mm diameter fibers
(350mm length)
Larger pendulum thermal noise and lower violin mode frequencies 22 22 22 22 22 22

23. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
Pendulum thermal noise (Thermoelastic) 　
Below 80K, thermoelastic noise does not matter.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Sensitivity of 2nd generation 23 23 23 23 23 23

24. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
Sensitivity of 2nd generation
Pendulum thermal noise (Brownian) 　
Below 30K, thermal noise is enough small.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 24 24 24 24 24 24

25. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
Violin modes　
Thin wire (0.6mm) Thick wire (1.6mm)
Sapphire Silicon Sapphire Silicon
343Hz Hz Hz Hz
698Hz Hz Hz Hz
1075Hz Hz Hz Hz
First violin mode might be too low.
AdLIGO : 511Hz
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
A.V. Cumming et al., Classical and Quantum Gravity 29 (2012) 25 25 25 25 25 25

26. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
Violin modes　
Thin wire (0.6mm) Thick wire (1.6mm)
Sapphire Silicon Sapphire Silicon
343Hz Hz Hz Hz
698Hz Hz Hz Hz
1075Hz Hz Hz Hz
First violin mode might be too low.
Solution : Larger mirror with smaller absorption
In any case, larger mirror is necessary for 3rd generation to reduce standard quantum limit.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 26 26 26 26 26 26

27. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
For vibration isolation, they must be thin.
8 K
Intermediate mass
10K-16K
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Mirror
13 K - 23 K
Absorption in mirror
0.1W – 1W 27 27 27 27 27 27

28. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
A : Cross section
l : Length
15 K (9.75K)
A/l = 10-5 m
(4*10-6 m)
A/l = 10-4 m
(3*10-5 m)
8 K
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Intermediate mass
16K(10K)
Mirror
23 K(13K)
Absorption in mirror
0.1W – 1W 28 28 28 28 28 28

29. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
Thick heat link (cross section could be on the order of cm2) should be an issue.
Solution : Larger mirror with smaller absorption
In any case, larger mirror is necessary for 3rd generation to reduce standard quantum limit.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 29 29 29 29 29 29

30. 3. Challenges for cooling
3-1. How to keep temperature with heat load ?
(b)Heat path
Thick heat link (cross section could be on the order of cm2) should be an issue.
(1)Many thin fibers (softer)
(2)Soft vertical spring and extra vibration isolation system for heat links is necessary.
Soft vertical spring
Extra pendulum for vibration isolation
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Investigation is in progress.
D. Chen et al., Classical and Quantum Gravity 31(2014) 30 30 30 30 30 30

31. 3. Challenges for cooling
3-2. Short initial cooling time
Since we discuss difference between 20K and 120K,
here, we consider initial cooling time below 120K.
Y. Sakakibara et al., CEC/ICMC2013, 2EOrD4-03, Anchorage, USA (2013).
20 days
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 31 31 31 31 31 31 31 31 31 31 31 31 31

32. 3. Challenges for cooling
3-2. Short initial cooling time
A : Cross section
l : Length
Bottle neck !
15 K (9.75K)
A/l = 10-5 m
(4*10-6 m)
A/l = 10-4 m
(3*10-5 m)
8 K
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Intermediate mass
16K(10K)
Mirror
23 K(13K)
Absorption in mirror
0.1W – 1W 32 32 32 32 32 32

33. 3. Challenges for cooling
3-2. Short initial cooling time
Some kinds of tricks are necessary.
(a)Mechanical thermal switch
between payload and crycoolers
(b)Softer vertical spring or thicker heat links with better vibration isolation systems
Softer vibration isolation
Better vibration isolation system
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Thicker heat links 33 33 33 33 33 33

34. 4. Summary Operation below 20K (1)How much is the noise below 20K ?
All kinds of thermal noise is smaller
than goal sensitivity of 2nd generation.
That’s all. Thank you for your attention.

35. 4. Summary Operation below 20K
(2)However, cooling below 20K is challenge.
Heat path is an issue. We need “thick” heat path.
It implies low violin modes and large external
vibration effect.
Solution
Larger mirror with smaller absorption
Vibration isolation
Thermal switch
That’s all. Thank you for your attention.

36. Thank you for your attention !
That’s all. Thank you for your attention.

37. 2. Noise vs Temperature
Motivation : Why the mirrors and suspension are cooled ?
(1)Small thermal noise
(2)Small thermal lens
(3)Less serious parametric instability
(4)Small cosmic ray effect
Kenji Numata and Kazuhiro Yamamoto,
”Chapter 8. Cryogenics”, in ”Optical Coatings and Thermal Noise in Precision
Measurement” Cambridge University Press (2012).
T. Tomaru et al., Classical and Quantum Gravity 19 (2002) 2045.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
K. Yamamoto et al., Journal of Physics: Conference Series 122 (2008)
K. Yamamoto et al., Physical Review D 78 (2008) 37 37 37 37

38. 2. Noise vs Temperature
Motivation : Why the mirrors and suspension are cooled ?
(2)Small thermal lens
Below 20 K : Several orders of magnitude smaller
(Higher thermal conductivity and smaller temperature coefficient of refractive index)
T. Tomaru et al., Classical and Quantum Gravity 19 (2002) 2045.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 38 38 38 38

39. 2. Noise vs Temperature
Motivation : Why the mirrors and suspension are cooled ?
(2)Small thermal lens
120K : 10times smaller
Thermal conductivity is 10times larger.
Temperature coefficient of refractive index is almost independent of temperature between 120K and 300K.
But it does not matter ?
J. Komma et al., Applied Physics Letters 101 (2012)
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
J. Degallaix,”Cryogenic interfetometers”,
in ”Advanced Gravitational Wave Detectors”
Cambridge University Press (2012). 39 39 39 39

40. 2. Noise vs Temperature
Motivation : Why the mirrors and suspension are cooled ?
(3)Less serious parametric instability
If larger beam is adopted to reduce thermal noise, number of instability modes increases.
K. Yamamoto et al., Journal of Physics: Conference Series 122 (2008)
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 40 40 40 40

41. 2. Noise vs Temperature
Motivation : Why the mirrors and suspension are cooled ?
(4)Small cosmic ray effect
K. Yamamoto et al., Physical Review D 78 (2008)
Below 20K,
this decay time is much shorter
(than that above 120K).
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 41 41 41 41

42. 2. Noise vs Temperature
Motivation : Why the mirrors and suspension are cooled ?
(4)Small cosmic ray effect
K. Yamamoto et al., Physical Review D 78 (2008)
Around 120K (silicon),
this amplitude is smaller.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 42 42 42 42

43. 2. Operative temperature
In principle, lower temperature is better.　
> 50K
Constant
<20K
Enough small
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Sapphire 43 43 43 43 43 43

44. 2. Operative temperature
In principle, lower temperature is better. But there is an exception. 　
Silicon
120K
Thermoelastic noise
vanishes.
Temperature control is necessary.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Silicon 44 44 44 44 44 44

45. 2. Operative temperature
120K operation (LIGO Voyager)
Heat absorbed in mirror : Several W
Heat extraction : Radiation, 13 W/m2 at most
Black coating on mirror is necessary.
It should have small mechanical dissipation and so on.
Fibers has lower conductivity (1000W/m/K). Diameter must be a few times larger at least
(a few mm).
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 45 45 45 45 45 45

46. 3. Suspension T. Sekiguchi, K. Somiya, K, Yamamoto 46 46 46 46
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
T. Sekiguchi, K. Somiya, K, Yamamoto 46 46 46 46

47. 3. Cooling time 3-1 Initial cooling of radiation shield
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
When power of heat extraction is 100 W,
the cooling time is 14 days.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 47 47 47 47 47 47

48. 3. Cooling time 3-1 Initial cooling of radiation shield
Heat extraction power
Pulse tube cryocooler : 100 W (above 60K)
in KAGRA (two cryocoolers).
C. Tokoku et al., CEC/ICMC2013, 2EPoE1-03, Anchorage, USA (2013).
Experiment showed that it takes 15 days to cool the radiation shield.
Y. Sakakibara et al., Classical and Quantum Gravity 31(2014)
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 48 48 48 48 48 48

49. 3. Cooling time 3-3 How to reduce cooling time
(1)Short cooling of radiation shield
Cooling bath (liquid nitrogen and helium):
Latent heat of liquid nitrogen is 200J/g.
700kg (900l)liquid nitrogen is necessary for KAGRA.
Complicate circulation system is also necessary and it could be path of vibration.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 49 49 49 49 49 49

50. 3. Challenges for cooling
How to keep temperature with heat load ?
If we use liquid helium …, 48g liquid helium evaporated (1W heat load) !
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 50 50 50 50 50 50

51. 3. Cooling time Current status (KAGRA case)
Y. Sakakibara et al., Classical and Quantum Gravity 31(2014)
Radiation
Payload with black coating
Follows shield.
Heat link
When thicker ones are adopted,
Vibration transmission should be an issue.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Cooling radiation is consistent with
Calculation. 51 51 51 51 51 51

52. 3. Cooling time 3-3 How to reduce cooling time
(2)Short cooling of payload below 100K
Thicker heat link should be an issue because of external vibration transmission. Extra vibration isolation system for heat links is necessary.
D. Chen et al., Classical and Quantum Gravity 31(2014)
Extra pendulum for vibration isolation
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 52 52 52 52 52 52

53. 3. Cooling time 3-3 How to reduce cooling time
(2)Short cooling of payload below 100K
Heat path with thermal switch
Gas : Radiation shield should keep gas.
All holes for laser beam and bar
from room temperature part are closed.
During cooling, main laser beam
can not observe drift of mirror.
Super insulator absorbs helium gas.
It takes longer time to evacuate helium gas.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 53 53 53 53 53 53

54. 3. Cooling time 3-3 How to reduce cooling time
(2)Short cooling of payload below 100K
Heat path with thermal switch
Mechanical thermal switch
between payload and crycoolers
Large heat contact during initial cooling (force)
Large thermal isolation after initial cooling
(soft metal for contact disturbs detachment)
Thermal switch on suspended object
Direction and position of mirror should be
changed after this switch is turned off.
Mechanism must work at cryogenic temperature.
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 54 54 54 54 54 54

55. 3. Cooling time 3-3 How to reduce cooling time
(2)Short cooling of payload below 100K
Other method ?
Optical cooling (so far, above 100K)
Near field radiation
Small gap (mm) enhance heat transmission of
radiation (photon tunneling). Does it work
below 100 K ?
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector. 55 55 55 55 55 55

56. Kenji Numata and Kazuhiro Yamamoto,
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Kenji Numata and Kazuhiro Yamamoto,
”Chapter 8. Cryogenics”, in ”Optical Coatings and Thermal Noise in Precision
Measurement” Cambridge University Press (2012). 56 56 56 56 56 56

57. Kenji Numata and Kazuhiro Yamamoto,
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Kenji Numata and Kazuhiro Yamamoto,
”Chapter 8. Cryogenics”, in ”Optical Coatings and Thermal Noise in Precision
Measurement” Cambridge University Press (2012). 57 57 57 57 57 57

58. Kenji Numata and Kazuhiro Yamamoto,
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Kenji Numata and Kazuhiro Yamamoto,
”Chapter 8. Cryogenics”, in ”Optical Coatings and Thermal Noise in Precision
Measurement” Cambridge University Press (2012). 58 58 58 58 58 58

59. Kenji Numata and Kazuhiro Yamamoto,
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Kenji Numata and Kazuhiro Yamamoto,
”Chapter 8. Cryogenics”, in ”Optical Coatings and Thermal Noise in Precision
Measurement” Cambridge University Press (2012). 59 59 59 59 59 59

60. Kenji Numata and Kazuhiro Yamamoto,
OK, what is cryogenic payload ? This is the cross section of tunnel of LCGT. This tall tower is vibration isolation system. There is cryogenic payload under this vibration isolation. Cryogenic payload is in cryostat. Payload includes mirror, which is the most important part of gravitational wave detector.
Kenji Numata and Kazuhiro Yamamoto,
”Chapter 8. Cryogenics”, in ”Optical Coatings and Thermal Noise in Precision
Measurement” Cambridge University Press (2012). 60 60 60 60 60 60