CHERCAM: The Cherenkov imager of the CREAM experiment

A Cherenkov imager, CHERCAM (CHERenkov CAMera), has been designed and built for the CREAM (Cosmic-Ray Energetic and Mass) balloon-borne experiment. The instrument will perform charge measurements of nuclear cosmic-ray over a range extending from proton to iron. It will achieve individual charge separation of the elements over this range [M. Buénerd, et al., in: 28th ICRC, Tsukuba, Japan, OG 1.5, 2003, p. 2157. [2]] (0.25 charge unit rms), allowing measurements of the energy spectra of individual elements by the CREAM instrument in the energy range from 1010 to 1015eV. CHERCAM is a proximity focused imager, based on a dedicated mechanical structure, equipped with an n=1.05 silica aerogel radiator plane, separated by a 12cm ring expansion gap from a photon detector plane consisting of a 1600 photomultiplier array, backed with dedicated front-end readout electronics. A prototype of the detector has been recently tested with 100 and 300GeV/c Z=1 particle beams at CERN. The contribution reports on both the beam test results of the prototype, and of the counter performance in ground operation.