Current status and future prospects of the CRAFFT project for the next generation UHECR observatory

A key to understand the origin of the Ultra High Energy Cosmic Ray (UHECR) is higher statistics with the composition information. One of the concepts to realize the future huge observation is an array of simple and low cost fluorescence telescopes. The fluorescence telescope can measure not only the arrival direction and energy spectrum but also the mass composition which is the important information to understand the origin of UHECR. A concept of a simple FD is to reduce the cost by changing from the imaging with multiple PMTs to the time information of a few PMTs, and minimization of the optical system by focusing the high energy events. In order to demonstrate this concept, we are developing Cosmic Ray Air Fluorescence Fresnel lens Telescope (CRAFFT), which further reduces the cost by using Fresnel lens and stand alone system without telescope hut unlike existing fluorescence detector in present UHECR observatory. We have constructed four prototype CRAFFTs and observed air showers by simultaneous observation with Telescope Array. By those study, the cost of a simple FD reaches 1/10 of that of a present FD.