Chaotic oscillations enhanced by magnetosonic waves in plasma-filled traveling-wave tubes

Abstract

A theory of plasma-filled traveling-wave tubes (TWTs) is developed in which the effect of magnetosonic waves excited in plasma by the operating wave is taken into account. These waves are excited by the ponderomotive force caused by the radial inhomogeneity of the axial component of the electric field of the operating wave. In the simplest case considered in the paper, this effect leads to an additional reactive nonlinearity in the wave envelope equation. This leads to a shrinkage of the region of stable oscillations in TWTs with the feedback causing the self-excitation; at the same time, the region of stochastic oscillations becomes larger. The radiation spectrum of stochastic oscillations in plasma-filled TWTs in which magnetosonic waves are excited is much wider and more continuous than the spectrum of stochastic oscillations in vacuum TWTs with the same feedback.

Generation of chaotic radiation in a driven traveling wave tube amplifier with time-delayed feedback

“…Subsequent increasing of either the amount of feedback or the TWT gain result in a period-doubling transition to chaos. 10,15,16,24,26 For a TWT with a narrowband filter in the feedback leg, therefore, the role of the phase nonlinearity becomes subsidiary and basically leads to a nonlinear frequency shift leading to more uniform spectrum in the chaotic regime. It has been observed, for example, that in a nonstationary regime with strong amplitude modulation, the effect of the AM/PM nonlinearity causes "wobbling" of the basic frequencies and thus broadening of discrete spectral lines.…”

“…In this case, the self-modulation is caused by the presence of a steep negative slope in the AM/AM curve. 10,15,16 The qualitative explanation to the amplitude mechanism is as follows. Consider the stationary regime when the TWT gain is close to or equal to the feedback attenuation.…”

“…Numerous results as given in Refs. [15][16][17][18][19] show that in this case the self-modulation mechanism and transition to chaos sce- …”

Research on Compact, High-Energy, Microwave Sources (MURI '94)

“…Ponderomotive effects in plasma-filled microwave tubes were analyzed in [63,64], where it was shown that these effects may lead to various nonstationary phenomena. Recall that the ponderomotive force f p is the force that acts on electrons moving in a slightly inhomogeneous electromagnetic field.…”

“…In the presence of plasma waves the system may exhibit some mode hopping effects, e.g., from a mode with two axial variations to a mode with three variations. In [64], a plasma-filled TWT was studied. It considered the case of a plasma column of small radius at finite magnetic fields when the ponderomotive force caused by the radial inhomogeneity of |£*| 2 …”