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Plasma wave wigglers for free-electron lasers

We explore the possibility of using a relativistic plasma density wave as a wiggler for producing free-electron laser radiation. Such a wiggler is a purely electric wiggler with frequency ω p (plasma frequency) and wavenumber k p . If an electron beam is injected parallel to the plasma wave wavefront, it is wiggled transversely with an apparent wiggler wavelength \lambda_{w} = 2\pi c/\omega_{p} . Using plasma densities in the 1017(cm-3) range, λ w of order 100 μm may be obtained, thereby permitting generation of short wavelength radiation with modest energy beams. The effective wiggler strength a_{w} = eA/mc^{2} \sim 0.5 can be extremely large. We discuss the excitation methods for such wigglers and examine the constraints imposed by the plasma medium on FEL gain in this scheme.