Experimental Observation of Suppression of Coherent-Synchrotron-Radiation–Induced Beam-Energy Spread with Shielding Plates

We describe the first direct observation of the significant suppression of the energy spread induced by coherent synchrotron radiation by a pair of conductive plates placed inside a dipole magnet. In addition to various feedback loops improving the energy stability of the beam parameters, our key innovation for this experiment is the observation of the time-resolved energy variation within the electron bunch, instead of the traditionally measured rms energy spread. We present the results of the experiments and compare them with a rigorous analytical theory.