Mode dynamics in a free electron maser with broadband frequency-dispersive feedback

Abstract

For a free-electron oscillator, problems of mode dynamics are studied for a case when the feedback has a wide, but finite band (the feedback coefficient depends on the frequency). It is shown that even a broadband frequency-dispersive feedback can significantly affect both the electron-current threshold of stability of the single-mode operation and the process of frequency tuning.

Nonstationary behavior in a delayed feedback traveling wave tube folded waveguide oscillator

“…Similar processes have been studied for free-electron laser ͑FEL͒ oscillators. 22,23 All the described phenomena are also typical for other multimode delayed-feedback oscillators. [19][20][21] …”

On the theory of self-modulation instability in an FEL amplifier due to stimulated scattering of counterpropagating waves

“…The nonstationary theory of BWO and TWT uses an effective technique based on transition to a moving reference system, which permits one to consider only the electrons located on the length of one wave period and thereby reduces drastically the calculation volume. This technique has been employed in many papers on the FEL theory (see, e.g., [18][19][20]), but it can be used only if the velocity of the electron beam is greater than the group velocity of the wave. We consider the opposite case since the light-speed waves, whose group velocity is equal to the speed of light, participate in the interaction.…”

“…Frequency dispersion of the feedback coefficient[19,20] can serve as an alternative factor limiting the amplification band width in an FEL oscillator.…”

Long-Pulse Operation at Constant Output Power and Single-Frequency Mode of a High-Power Electrostatic Free-Electron Maser with Depressed Collector

“…The method of description of the mode competition in a dispersive-feedback cavity of a special type used in the FFF was developed in the Letter [11]. Since the experimental results of the FFF in short pulse setup have been accurately predicted by Savilov et al [4,17], we proceed following these theoretical models. In an oscillator, such as FEM, the issue of possible multimode operation is related to the parameter of excess over threshold, L. This is a dimensionless parameter which is proportional to the length of the interaction region, because in the simplest model it is defined as the product of this length and the cubic root of the electron beam current.…”

“…If L exceeds its starting value and is less than some threshold, the single-mode operation is stable. If L exceeds the threshold of single-mode operation, complex multimode operation can take place, with fast fluctuations in output power due to beating of the excited modes [17].…”