RIPPLED BEAM FREE-ELECTRON LASER-AMPLIFIER USING THE AXIAL FREE-ELECTRON LASER INTERACTION

A new microwave generation mechanism involving a scalloping annular el ectron beam is discussed. The beam interacts with the axial electric f ield of a TM0a mode in a smooth circular waveguide through the axial f ree-electron laser interaction, in which the beam ripple period is syn chronous with the phase slippage of the rf mode relative to the electr on beam. In this gaper, we analyze the ripple motion of the electron b eam and derive the dispersion relation describing the exponential grow th of the rf mode. We calculate the gain for a nominal design and as a function of beam current and ripple amplitude, and show that power ga in on the order of 30 dB/m of interaction is achievable. We additional ly demonstrate that, under the right conditions, the interaction is au toresonant. (C) 1997 American Institute of Physics.