Explaining the European XFEL X-ray Optics and Photon Diagnostics tunnel components

These videos were recorded in December 2020 for educational purpose addressing bachelor students in the frame of the HERCULES School 2021.

[@Garganzuul]

Is it possible to decelerate the electron beam and spread it laterally to form an electron-only diffraction grating at sub-atomic scale?

[@EuropeanXFEL]

Dear Garganzuul, we take great efforts and almost 2 km of linear accelerator to produce an electron beam with very high energy of up to 17.5 GeV. Also, there are special electron beam focusing elements that help maintaining a particularly small transverse beam size (small emittance). Wouldn't it be a waste to decelerate and defocus these special electrons since we could just use another electron beam for that purpose ? In any case one would need something more substantial than electrons to scatter x-rays sufficiently. Besides, it is these high energy electrons that create the X-ray laser beam in the first place, thus if sufficiently dispersed laterally (large emittance beam), no lasing would occur and we wouldn't have any x-ray laser radiation to scatter from anything.