GRACE is a five element array of air Cherenkov light collectors designed to measure the energy of primary cosmic rays and operate on the terrain over the deep underground muon tracking detector, MACRO, at the Gran Sasso National Laboratory in Italy. The coincidence detection of air Cherenkov photons and deep underground muons produced in extensive air showers will allow an association of the primary energy with the muon events observed underground. We present detailed Monte Carlo calculations of the expected signal, a complete description of our detectors and test results of their initial deployment at the University of Michigan Peach Mountain Observatory.
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We are grateful to the directorship and staff of Laboratori Nazionali dal Gran Sasso for their cooperation and encouragement . We thank Jim Gaidos at Purdue Jnivcrsity for his ideas on Cherenkov telescope construction, Giulio Auriemma for helpful discussions, the University of Michigan Department of Astronomy for the use of the Peach Mountain facility and Jim Stone at Boston University for supplying us with PMI's . We are especially thankful to Beth Demkowski for her unfailingly cheerful editing assistance . This work was partially funded by Department of Energy and the University of Michigan Phoenix Memorial Reactor.