We have evaluated a 20-in. photoelectric lens image intensifier tube (PLI) tobe mounted on the spherical focal surface of the Ashra light collectors, whereAshra stands for All-sky Survey High Resolution Air-shower Detector, anunconventional optical collector complex that images air showers produced byvery high energy cosmic-ray particles in a 42$^circ$-diameter field of viewwith a resolution of a few arcminutes. The PLI, the worlds largest imageintensifier, has a very large effective photocathode area of 20-in. diameterand reduces an image size to less than 1-inch diameter using the electric lenseffect. This enables us to use a solid-state imager to take focal surfaceimages in the Ashra light collector. Thus, PLI is a key technology for theAshra experiment to realize a much lower pixel cost in comparison with otherexperiments using photomultiplier arrays at the focal surface. In this paper wepresent the design and performance of the 20-in. PLI.
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