1. 1 Kazuhiro Yamamoto Institute for Cosmic Ray Research The university of Tokyo Current status KAGRA(LCGT) cryogenic payload meeting 7 March2012

2. 2 Baffles for scattered light Meetings 15 th of Feb. : AOS cryopayload meeting 17th of Feb. : Stray-Light Control meeting 2nd of Mar. : Stray-Light Control meeting (a)Small angle scattering and scattering on the edge of baffles: Baffle in (room temperature) duct can stop scattered ligjht. (b)Large angle scattering : Baffle in cryostat is necessary. (c)Scattered power is about 10ppm. Almost all power is in large scattered light (From Hiro Yamamoto). (d)Idea of Kimura: 2 cryocoolers for shield, the other 2 ones for payload. Even if baffle connected to shield absorbs the light, temperature of payload do not become higher.

3. 3 (e)Mike Smith has already given idea for baffle in cryostat and calculated the scattered light effect in detector sensitivity. Fortunately, the effect is not so large. However, suspension is necessary (resonance of baffle itself is a problem). Discussion for details are in progress. (f) Investigation for vibration of radiation shields should be in progress. Baffles for scattered light

4. 4 Idea of Mike

5. 5

6. 6 Heat links Current idea : Heat links are between radiation shield and platform. (a) Radiation shield is farther than previous design. (b) Another idea : Heat link between radiation shield and intermediate recoil mass. Is also necessary heat links between intermediate recoil mass and intermediate mass ? T. Sekiguchi and Y. Sakakibara are Investigating (mechanical and thermal simulation) now.

7. 7 Mirrors (a)Ears for sapphire fibers New KAGRA collaborator SICCAS ‐ GCL Crystal Research & Development Center http://gwdoc.icrr.u-tokyo.ac.jp/cgibin/DocDB/ShowDocument?docid=820 They can process (cut and so on) sapphire bulk. K. Yamamoto discussed this issue with Lihe Zheng and Jingya Wang (9 th of Feb.). They said that it is possible in principle, but primary tests are necessary. (b) Huge a-axis sapphire: Although Prof. Mio said that it can be used for 1/4 cryostat, E. Hirose suggested that mirror group might use it. We should look for something else.

8. 8 Mirrors Ears for sapphire fibers

9. 9 Mirrors (c) Coating mechanical loss measurement E. Hirose and K. Yamamoto transfered the experimental apparatus from KEK to ICRR. The progress might be rapid... (d) Book for sapphire was bought. Sapphire: Material, Manufacturing, Applications (Micro- and Opto-Electronic Materials, Structures, and Systems) Elena R. DobrovinskayaElena R. Dobrovinskaya (Author), Leonid A. Lytvynov (Author), Valerian Pishchik (Author) SpringerLeonid A. LytvynovValerian Pishchik http://www.amazon.com/Sapphire-Manufacturing-Applications-Opto-Electronic-Structures/dp/144194673X/ref=sr_1_1?s=books&ie=UTF8&qid=1331038835&sr=1-1 You can find the details of sapphire.

10. 10 Digital system Osamu Miyakawa, who is the chief of digital system, called K. Yamamoto yesterday (7th of Mar.). Digital group have already constructed many digital systems, but, only a few system are used by the other sub-group. Osamu looks for the sub-groups to use digital system. Digital system for temperature monitor ? 1/4 cryostat is a good test facility. We should discuss this topic.

11. 11 Fresh person Chen Dan, who becomes the graduate student in Ph.D. cource on the next April, will starts his research for cryogenic payload. Other Ph.D. Students : Takanori Sekiguchi Yusuke Sakaibara

12. 12 To do list Document for external review : dead line is 17th of Mar. Evaluation for budget of cryogenic payload Preparation for bidding of 1/4 cryostat