Status of the SPHERE experiment
  Here is presented the current state of the SPHERE-2 balloon-borne experiment. The detector is elevated up to 1 km above the snow surface and registers the reflected Vavilov-Cherenkov radiation from extensive air showers. This method has good sensitivity to the mass-composition of the primary cosmic rays due to its high resolution near the shower axis. The detector consists of a 1500 mm spherical mirror with a 109 PMT cluster in its focus. The electronics record a signal pulse profile in each PMT. In the last 2 years the detector was upgraded: time resolution of pulse registration was enhanced up to 12.5 ns, channel sensitivity was increased by a factor of 3, a new LED-based relative PMT calibration method was introduced, and new hardware and etc. was installed. 
R. A. Antonov (1), S. P. Beschapov (2), E. A. Bonvech (1), D. V.   Chernov (1), T. A. Dzhatdoev (1), Mir. Finger (3), M. Fin...
astro-ph.IM astro-ph.HE physics.ins-det