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

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.

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

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

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

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

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

2. Before installation at site Yusuke Sakakibara (ICRR at that time) conducted experiment. Y. Sakakibara et al., Classical and Quantum Gravity 31(2014)224003. 8 8 8 8 8 8 8 8 8

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

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

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

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)224003. 12 12 12 12 12 12 12 12 12

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)224003. 13 13 13 13 13 13 13 13 13

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

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

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

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.

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 K @ shield line 6 & 12.5 K @ cryo payload line ~15 K @ 8 K shield

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.

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

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 ?

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.

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.

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.

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.

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.

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