makes use of the de-commissioned THEMIS solar electrical plant in the French Pyrénées. A
large (2000 m 2) mirror surface area from 40 independent heliostats followed by a
secondary optic, a trigger system using analog summing techniques and signal digitization
with 1 GHz flash ADCs make possible the detection of cosmic γ-rays down to 30 GeV. This
paper provides a detailed technical description of the CELESTE installation.