A polychromatic FEL light source using a single electron beam and multiple wigglers

The electron beams in free-electron lasers (FELs) are typically used in one (or more) wigglers located in a parallel switchyard arrangement, and each bunch is used once per wavelength. However, it is possible to position wigglers in series and use the same electron bunch to obtain a variety of wavelengths with little or no degradation in efficiency in each wiggler if successive wigglers are tuned to progressively longer wavelengths. This is because the energy spread induced on the beam by the interaction in one wiggler will not be enough to degrade the interaction in another wiggler that is tuned to a sufficiently longer wavelength. Here, the 3D polychromatic simulation code, MEDUSA, is used to simulate the interaction in a series of wigglers, where the first wiggler is tuned to operate at a wavelength of 1.5 إ corresponding to the design parameters for the LCLS.