Zero slippage operation of TEUFEL

The Free Electron Laser in Twente TEUFEL is very suitable to operate near zero
slippage conditions. The resonator is a waveguide structure with hole coupling for the electron beam to enter and exit and to out-couple the light. Due to the long wavelength, the diameter of the waveguide can have macroscopic dimensions to significantly affect the group velocity of the generated light via the dispersion relation. Whereas the longitudinal phase-velocity has to be equal to the longitudinal velocity of the electrons to be at resonance, the longitudinal group velocity has to be equal the longitudinal velocity of the electrons too, to operate in the zeroslippage regime. Both conditions can be fulfilled in a waveguide. Advantage of operation in the zero-slippage regime is to allow short pulse operation at high gain. The energy density of the light travels with the electron pulse. For our FEL we expect operation with the following parameters: Electron energy 4 MeV; diameter of circular waveguide 3.2 mm; generated wavelength 658 mm; pulse duration 25 ps. Due to the high quality beam, i.e. high current and low emittance we expect high gain.