Outline of the Detector

Photo-Multiplier-Tubes (Inner detector)

The inward-facing 11,129 photo-sensors, called photo-multiplier-tubes (PMTs) are instrumented in the inner tank. The Cherenkov light emitted by charged particles running in water is detected by these sensors. The energy and direction of the charged particle is calculated by the information of the detected charge and timing. This PMT is developed with Hamamatsu-photonics. The diameter of the photosensitive area is 20 inch (about 50cm) and is the largest in the world.



In November 2001, an apparent cascade of implosions triggered by a single PMT implosion destroyed over half of the PMTs in water.


After 2005, in order to avoid chain reactions of implosions even if a single PMT implosion is happen, all of inner PMTs are covered with acrylic and fiberglass shields.



The inner PMTs are instrumented at intervals of 70cm and cover about 40% of the detector wall. The rest of the surface is covered with black polyethylene terephthalate sheet which optically separates the tank to the inner part and the outer part.


Details of PMTs




Outline of the Detector