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 w p (plasma frequency) and wavenumber k,,. If an electron beam is injected parallel to the plasma wave wavefront, it is wiggled transversely with an apparent wiggler wavelength X, = 27rc/wp. Using plasma densities in the 10" (cm-') range, X, of order 100 pm may be obtained, thereby permitting generation of short wavelength radiation with modest energy beams. The effective wiggler strength a, = e A / m c 2 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