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Test of improved prototype and new anti-chain-implosion covers

The large size photo-sensor is encapsulated in a cover to prevent possible chain implosion in deep water. Deeper the detector is, the higher water pressure is.

For Hyper-Kamiokande, which have about 60m depth, it is a important item to develop a more powerful cover than that for current Super-Kamiokande (about 40m depth). To establish the cover, we need to prove actual prevention of chain implosion in deep water. We already performed a test of a prototype in 2016, and we established an anti-chain-implosion cover for Hyper-Kamiokande.

In March 2018, we tested three type of covers, improved prototype, resin-made monolithic cover, a tube-shaped stainless steel made cover which is developed by our Spanish group (Picture 1 to 3).

(Picture 1) Test system. A photosensor with cover is located at the center of the grid, and surrounded by bare photosensors. The system is lowered down to deep water. The photosensor in the cover is crashed by a special tool (“pusher”) remotely and see the effect on the surrounding photosensors. Center is photosensor with the improved prototype. We put color tapes on glasses or cover surface to identify the surface via camera.
(Picture 2) A resin-made monolithic cover. It is much lighter than current prototype made by stainless steel.
(Picture 3) A tube-shaped cover developed by our Spain group. Structure is relatively simple and cheaper production cost is expected.

We carried out the test from March 6th to March 10th in old JAMIC (Japan Microgravity Center) building in Kami-Sunagawa city, Hokkaido, Japan (Picture 4).

We proved that the covers prevents chain implosion in 80m, 40m, and 60m, respectively. We also found differences of the shockwave generation depending on the covers and different deformation of covers, which are important to understand the process of implosion of large photo-sensor in deep water. In addition to that, we tested an implosion of smaller (8 inch diameter) photosensor in deep water, and we tested a new type of test apparatus to crash photosensors.

We successfully took such valuable data in short time. This is fully supported by Kami-Sunagawa town.

(Picture 4) Old JAMIC (Japan Microgravity Center) building in Kami-Sunagawa city, Hokkaido, Japan
(Picture 5) During the test, lowest temperature in the laboratory was below minus 10 degree. This is icicles on a rope in laboratory.