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A short summary of the physics behind laser-driven plasma wakefield acceleration, electron-beam driven plasma wakefield acceleration and laser-driven structure acceleration is provided.
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These emerging acceleration technologies, along with alternative photon-generation techniques, are reviewed in this paper. Specifically, laser-driven plasmas, , and structures, as well as electron-beam driven plasmas, , have the promise to provide compact and cheap generation and acceleration of electron bunches that can provide a new paradigm of X-ray light sources in universities and small laboratories worldwide as well as significantly cheaper national-level high average flux hard X-ray sources. However, remarkable new source and acceleration technologies are now emerging that will have significant impacts on future light sources. Because of the cost and size of this type of machine using conventional microwave accelerator technology, where the maximum accelerating gradient is limited to less than 100 MeV/m, it is hard to imagine that more than a few will be built, and the small number will create a severe bottleneck for enabling discovery science using coherent X-rays. Facility users will compete for time at the limited number of experimental stations. LCLS is a major facility, with standard S-band travelling-wave cavities extending over 1 km, to accelerate an electron beam up to 14.5 GeV. LCLS represents a very significant achievement, demonstrating new levels of electron beam and wiggler control. Light sources are entering a new era, with the success of the linac coherent light source (LCLS) as the first free-electron laser (FEL) operating in the hard X-ray regime.