A RING IMAGING CHERENKOV TELESCOPE FOR OBSERVATIONS OF HIGH-ENERGY COSMIC-RAYS

We describe a ring imaging Cherenkov counter for high altitude balloon flights designed to measure the energy spectra of cosmic ray nuclei above 40 GeV/amu. The instrument has a 3 m long nitrogen gas radiator at 1 atm, a spherical and planar mirror system, and almost-equal-to 2.2 m2 of TMAE/ethane photon detecting drift chambers with fused silica windows in the focal plane. The mirror system is designed such that cosmic ray particles which trigger the instrument cannot pass through the photon detectors. Cosmic ray trajectories through the instrument are determined by eight low mass drift chambers, each of 2.2 m2 area, which predict the ring image center to +/-0.76 mm. Ground tests with cosmic ray muons prior to the flight show that the detectors see about two photoelectrons from a high energy singly charged particle. Special efforts were made to ensure stable operation and constant temperatures and pressures under remote control during the balloon flight. In September 1991, this instrument flew for 31 h at an altitude of approximately 37 km and collected cosmic ray events which were transmitted to a ground station for recording.