[en] The paper is devoted to the investigation of the possibilities of a photoelectric registering system (photodetector) with a Cherenkov device designed for measurement of the mean beam energy in the phasotron of the Laboratory of Nuclear Problems. The photodetector consisted of an electron to optical converter on the micro-channel plate and a dissector type LI-605 connected by means of fiber optics. The photodetector is found to allow measurements of the Cherenkov radiation intensity distribution within a macroimpulse of the accelerator (∼ 40 μs) for a proton beam with the energy 655 MeV and intensity 10⁷ - 10⁸ protons/s. 4 refs.; 3 figs