Beam size measurement at high radiation levels

The small beam sizes below 100 mu m at the end of the Stanford Linear Accelerator require a good resolution of the measuring system. This is investigated. A high radiation level, which is produced by nearby collimators, forces the cameras to be moved to a remote location. An optical system has been built, which guides a 5-mm-wide picture with a resolution of about 30 mu m over a distance of 12 m to an accessible region. The overall resolution is limited by the screen thickness, optical diffraction and the line resolution of the camera. Vibration, chromatic effects or air fluctuations play a much less important role. The pictures are colored to get fast information about the beam current, size and tails. Beside the emittance, more information about the tail size and betatron phase is obtained by using four screens. First results are presented.<>