Mirror alignment control for COMPASS RICH-1 detector

The focusing system of the COMPASS RICH-1 detector consists of two segmented spherical mirror surfaces, formed by 68 hexagonal and 48 pentagonal individual elements. All individual mirrors have two degrees of freedom to adjust the angular alignment in order to obtain a continuous spherical surface. Relative angular misalignments can be monitored on-line by the CLAM method, based on the optical reconstruction of line images. Complementing the CLAM measurements with photogrammetry, the absolute mirror orientation and position in space can be determined too. The method is described, as well as the algorithms used to access the relative and absolute mirror alignment.