Stabilization of spatio-temporal dynamics of free-electron laser operation under effect of spread in electron velocity

The effect of velocity spread on the dynamics of the interaction of longitudinal modes is studied for a FEL-oscillator with broadband feedback. It is shown that the spread shortens the process of mode competition and increases the electron-current threshold of stable single-mode operation. In addition, the spread leads to a shift in the frequency of the excited mode to the range of the most efficient electron-wave interaction. This results in a very weak sensitivity of the efficiency to the spread.