Astrophysics - Instrumentation and Methods for Astrophysics
Beschreibung:
The Large Size Telescope (LST) of the Cherenkov Telescope Array (CTA) is designed to achievea threshold energy of 20 GeV. The LST optics is composed of one parabolic primary mirror 23 min diameter and 28 m focal length. The reflector dish is segmented in 198 hexagonal, 1.51 m flat toflat mirrors. The total effective reflective area, taking into account the shadow of the mechanicalstructure, is about 368 m2. The mirrors have a sandwich structure consisting of a glass sheetof 2.7 mm thickness, aluminum honeycomb of 60 mm thickness, and another glass sheet on therear, and have a total weight about 47 kg. The mirror surface is produced using a sputteringdeposition technique to apply a 5-layer coating, and the mirrors reach a reflectivity of94% atpeak. The mirror facets are actively aligned during operations by an active mirror control system,using actuators, CMOS cameras and a reference laser. Each mirror facet carries a CMOS camera,which measures the position of the light spot of the optical axis reference laser on the target of thetelescope camera. The two actuators and the universal joint of each mirror facet are respectivelyfixed to three neighboring joints of the dish space frame, via specially designed interface plate.