Suppression of Current Shot Noise and of Spontaneous Radiation Emission in Electron Beams by Collective Coulomb Interaction

The effect of current-shot-noise suppression in an electron beam (e-beam) and the corresponding process of charged-particle self-ordering are analyzed using an analytic 1-D model and verified by 3-D numerical simulations. The suppression of current shot noise can be utilized to enhance the coherence of seeded free-electron lasers (FELs) and any other radiation devices using an e-beam. It is shown that this can be attained at optical frequencies with state-of-the-art high-quality e-beams. Our analysis of spontaneous emission suppression results in fundamental theoretical limit expressions for the coherence of FELs and other coherent radiation devices, which is analogous to the Schawlow-Townes limit. After exceeding the shot-noise limit, the coherence of FEL radiation is limited in the IR by velocity noise due to the e-beam energy spread. At UV and shorter wavelengths, it is fundamentally limited by quantum noise.