Development of a 16" UV-ray image intensifier tube

We have developed a 16" UV-ray image intensifier tube (UVII) to form a spherical focal surface of an Ashra telescope. Ashra (all-sky survey high resolution air-shower detector) is a new air fluorescence and Cerenkov detector to observe TeV gamma rays, very high energy neutrinos, and extremely high energy cosmic rays. The UVII has a very large effective photocathode area of 16" diameter, and it reduces the image size into 1" diameter using the electric lens effect. This enables us to use a solid-state imager to take focal surface images of the Ashra telescope. Thus, the UVII is a key technology for the Ashra experiment to realize much lower pixel cost in comparison with other experiments using photomultiplier arrays as a focal surface. The UVII achieves high resolution of 3.4 Lp/mm at the input window. An output screen of the UVII is made of a fiber optic plate (FOP). The FOP has a concave shape to optimize the electric lens configuration under the fixed curvature of input window, resulting in almost uniform resolution within the whole sensitive area. We have adopted the P47 phosphor screen with 10% decay time of ∼100 ns. and have obtained an amplification factor of about 100. We will present the design, construction, and performance of 16" the UVII in this paper.