Possible scheme for observing acceleration (Unruh) radiation

In an FEL the electrons traveling through the undulator are surrounded in their own reference frame by Unruh radiation at a temperature of order 8,000 Kelvin. When these virtual photons scatter from the beam electrons they become real and can be detected. Because of the microbunching of the FEL electron beam this process proceeds coherently for a fraction of the electrons in the microbunch. This enhances the Unruh radiation which is still dominated by the copious spontaneous radiation in the same energy range. We discuss the particular case of the Stanford LCLS, as well as the case of extreme acceleration, when the x-ray beam is brought into collision with the 14 GeV electron beam.