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Coherent synchrotron radiation in an X-band photoinjector

A high-gradient, high-brightness X-band rf photoinjector is used to produce sub-picosecond electron bunches at energies in the 1.5-2 MeV range, which are propagated in a short section of corrugated waveguide, with an inner diameter of 10 mm, a corrugation period of approximately 2.5 mm, and a modulation depth of 1.5 mm. Extremely short rf pulses are measured, in the 100 ps -<5 ns range, corresponding to the slippage time between the electron bunch and the radiation produced by a coupling to the slow-waves supported by the waveguide structure. Coherence is measured by varying the bunch charge and verifying a quadratic scaling of the rf power; W-band radiation is produced using this new radiation mechanism, which may have very important potential applications in coherent millimeter-wave and THz radiation generation. We will discuss the technical details of the X-band rf gun and slow-wave circuit, as well as our experimental results, and a theoretical description of the interaction. A proposed millimeter-wave, chirped-pulse free-electron laser experiment using the X-band rf gun will also be discussed.