Interactions of Multiharmonic Space Charge Waves in Amplification Section of Superheterodyne Free Electron Laser

We analysed the multiharmonic interactions of space charge waves in the amplification section of the superheterodyne free electron laser in the submillimeter wavelength range within the framework of the cubic nonlinear approximation. We use an undulator with a longitudinal periodic reverse electrostatic field to amplify longitudinal waves. We researched the effect of generating an additional periodic reverse pump electric field by an electron beam. We demonstrate that the device can amplify multiharmonic signals without distorting of their amplitude spectra. With the given input parameters of the considering FEL, we found the feasible in practice values of the saturation length and level of the amplification of a terahertz signal. Also, for the first time, we studied the effect of generating an additional electric pump field due to the electron bunching in a relativistic electron beam in a linear approximation. We show that the resulting pump electric field increases by 33% due to this effect. This leads to an increase in the growth rate of space charge waves and a decrease in the saturation length by similar to 33%.