Experiment SPHERE status – 2006 and CR composition determination by means of Cherenkov light LDF

The modern status of the SPHERE experiment and the method to determine the primary energy and the kind of the primary nuclear particles is presented. The SPHERE experiment is based on A.E.Chudakov's suggestion to use a new method for investigating the ultra high energy primary cosmic ray energy spectrum [A.E. Chudakov, Trudy conf. po cosm. lutcham, (in Russian), p.69, Yakutsk, 1972]. A small device lifted above the snow surface of the Earth detects the Cherenkov light of extensive air showers reflected from the surface. The relatively simple detector SPHERE-2 (spherical mirror 1.5m diameter and retina of 100 pixels) is presented. The next plan of the SPHERE experiment is to start measurements of the cosmic ray spectrum in the energy range 1016–1018 eV above the snow surface of Lake Baikal.