Adaptive optics for the LEP 2 synchrotron light monitors

The image obtained with the LEP synchrotron radiation telescopes deteriorates, giving multiple and deformed images, when the beam energy goes beyond 80 GeV at beam currents above 2 mA. This problem is due to the deformation of the light extracting beryllium mirror, by as little as 1 mm, and had been predicted at the design stage. To overcome this problem, several changes together with an adaptive optics set-up have been introduced. These essentially consist of a cylindrically deformable mirror to compensate the cylindrical deformation of the beryllium mirror and a movable detector to compensate the spherical deformation. Both components are continuously adjusted as a function of beam current and energy.