Most folks are aware of the Doppler effect and the red-shift observed in stars and galaxies that are receding from us due to the expansion of the universe. Another fun aspect of synchrotron sources is that the light they emit is blue-shifted by that same Doppler effect (aka Lorentz transformation).

The idea that accelerating electrons emit light shouldn't be surprising: If I drive an antenna by varying the applied voltage with a frequency between 600 and 1500 kHz it will emit AM "radio waves" (aka light) which will then drive another (receiving) antenna causing electrons in that antenna to oscillate and using a germanium diode one can hear that signal in one's earphones. So you can think of the electrons in the storage ring as you would electrons in an antenna. The only difference is that the storage ring uses microwaves to accelerate the electrons because they are in a vacuum chamber rather than an antenna. So the electrons are accelerated using microwaves. They (in their rest frame) re-emit that microwave radiation as they accelerate (change direction). But because they are at 0.99999c the light that we see in the laboratory is blue-shifted into the x-ray regime. The result is a broad spectrum of light centered near 0.1 nm (1 Angstrom), which is the sweet spot for both x-ray diffraction and spectroscopy.

Rgds,
HH/Sean

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