Cryogenics for LCGT

Cryogenics for LCGT

Technical Advisory Committee for LCGT2005.08.23 ICRR

SUZUKI, ToshikazuHigh Energy Accelerator Research Organization

contents

• Achievements of CLIO cryogenics

• Objects to be cooled and requirements

• Heat transfer

• Cryocoolers

• Design examples of LCGT cryogenics

• Summary

Achievements of CLIO cryogenicsCooling down

• Full operation of cryogenic system with dummy mirror installation.

• A small Ohmic heater simulates a laser absorption.

• Temperature of cryogenic parts are cooled down to their designed values.

(T.Uchiyama , Fig.11 in Chapter 11, Technical Report of LCGT )

Achievements of CLIO cryogenicsCryocooler system with sub-m vibration

2nd V.R.Stage -> Heat LinkAmplitude ≃ 50 nm

Cold head -> Cryostat ≈ Seismic background

Achievements of CLIO cryogenicsVibration at 300K stage

• Red– PT Cryocooler:ON– Vacuum Pump :ON

• Blue– PT Cryocooler :OFF– Vaccuum Pump :OFF

• Cryocooler operation does not degrade seismic background at 300K stage.

K.Yamamoto

(Fig.12 in Chapter 11,Technical Report of LCGT)

Achievements of CLIO cryogenics

• Technology of cryocooler system with small vibration has been established.

• Cryocooler system can operate without affecting seismic background.

• Design of heat balance on cryogenic system was confirmed.

CLIO Cryogenics --> LCGT CryogenicsExtend

Heat generation on the mirror

T.Uchiyama,Technical Report of LCGT

T=20 K

q=290 mW ・ Design Safety factor

Mirror substrate : SapphireSuspension rods : Sapphire

Heat leaks from 300K to cryogenic parts • Conduction from SAS• Black body radiation fro

m holes• Conduction through su

pport of shields• Scattered Laser light• Conduction through ele

ctric cablings• Radiation to shields

Heat Load of Cryocooler

Heat Link Efficiency

(T.Uchiyama, Fig.2 in Chap.11, Technical Report of LCGT)

Heat flow of LCGT cooling system

(T.Tomaru, Fig.1 in Chap.13, Technical Report of LCGT )

8 K

4.2 K

Estimation of heat flow

(T.Tomaru, Fig.2 in Chap.13, Technical Report of LCGT )

Heat transfer in cryogenic GW detector

• Ultra-high vacuum– Conduction through solid

• Compatibility with vibration isolation– Large conductance for heat flow– Small conduction for mechanical vibration

• Small mechanical loss for mirror support

Mirror Support : large , small mechanical loss, large strengthFrom SPI to Cryocooler : large , small Young’s modulus From SAS to Platform : small , large strength

Material selection:Sapphire

• Sapphire is the only candidate for mirror support• Size effect for thin rod

(T.Tomaru)(T.Uchiyama)

€

= Ci∑ v ili

€

i :

C :Type of carrier

Specific heat

€

v :

l :

Velocity of the carrier

Mean free path

Material selection:Pure Al

• Material for heat links• Avoid size effect for our purpose• Inside cryostat -> single-wire• Cryostat-cryocooler -> multi-wire

(T.Tomaru, Fig.7in Chap.13,Tech. Rep. of LCGT)(T.Uchiyama, Fig.2 in Chap.12,

Tech. Rep. of LCGT)

99.9999 % Al Example of pure Al wire99.999% Al, 0.15 mm x 735

Material selection:amorphous metal

• SAS-Suspension platform

• Temperature gradient (300K-14K)

• Experience in the cryogenic resonant detector (60Hz)

Why cryocooler

• Intermittent charge• Variation of temperature

distribution• Transportation of liquid• Handling of evaporated

gas• Potential danger in deep

tunnel• Boiling noise• Liquefaction facilities

• Stationary operation• Stable distribution of

temperature• Electricity and cooling

water• Maintenance• Mechanical vibration• Cooling power

Cryocooler Liquefied gas

Typical cryocoolers

Cold stage~20 mCold head~20 m/sec2

Cold stage~20 mCold head~0.2 m/sec2

(T.Tomaru et al., Cryogenics, 44, ( 2004) 309-317 )

Cryocooler system for CLIO

(T.Tomaru, Fig.3 in Chap.13, Tech. Rep. of LCGT)

Requirements for cryocoolers

Heat load for LCGT cooling system

Cooling power and numbers of cryocoolers

(T.Uchiyama, Table 3 and 4 in Chap.11, Tech. Rep. of LCGT)

Increasing cooling power

CLIO PT cryocooler

0.5 W @ 4.2 K50 W @ 80 K

LCGT cryocooler

1 W @ 4.2 K100 W @ 80 K

◎ Compressor with larger capacity U=pV○ Increasing nubmers of cryocoolers with current model

☆ Cryocooler with 1W@4.2K already exist but not suitable for VRS type system.

Target will be attainable within the extension of current technology.

Design example of LCGT cryostat

Example of cryostat location

(T.Uchiyama, Fig.5 in Chap.11,Tech. Rep. LCGT)

Summary of LCGT cryogenics• Fundamental technology of cooling syst

em has been established.• The PT cryocooler system of CLIO with

low-level vibration have already satisfied the requirements of LCGT

• The way of increasing cooling power is attainable from current technology.

• Properties of key materials are known.• Scale up from CLIO to LCGT is availabl

e.

Vac. Pump

Compressor

Connection of cold head and valve table