First Stage Experiment on Optical Diffraction Radiation at KEK-ATF: Theoretical Approach

Extremely low emittance and high current electron beam is one of the vital characteristics for linear colliders or X-ray FEL's. Parallel developments of non-invasive beam diagnostics are strongly required for realizing such beams. Detection of Optical Diffraction Radiation (ODR), because of its non-destructive nature, is the most promising technique for the application to the non-invasive beam diagnostics; however, very little experimental investigations existed. Up to now Transition Radiation (TR) has widely been used for non-invasive beam diagnostics. That is because of high signal-to-noise ratio, instantaneous emission, large emission angles, and availability of detailed comparison with the theory. But in this case the particle directly interacts with a target that may lead to emittance growth. At KEK-ATF Damping Ring detailed investigation of Optical Diffraction Radiation is planed. The optimization of experimental conditions is required. A model for calculating the ODR characteristics from an ultrarelativistic charged particle distributed by Gaussian law and moving close to a tilted conducting screen has been developed. It is noticed that at the impact parameter (shortest distance between the particle trajectory and the target) comparable with beam size the TR is significant. Results of simulations based on the experimental conditions are also shown.