Filled With Plasma S-band Coupled-cavity Traveling Wave Tube Signal Analysis

Traveling wave Tubes(TWT)are high gain,broadband,high efficiency,and high power microwave amplifiers,which are widely used in modern military electronic equipments,such as communications,radars,electronic warfare,etc.It has been shown in many researches that by injecting plasma into the vacuum microwave devices,the interaction efficiency can be increased greatly,so that the output power can also be enhanced at the same input condition,and meanwhile the focusing magnetic field can be reduced or eliminated.The characteristics of large signal beam-wave interaction in the coupled-cavity TWT filled with plasma is studied in the dissertation.1.How the hybrid wave between the cavity mode and plasma mode is formed and expanded is studied.When the density of plasma increase to a certain scale,in this case, the cavity mode of the CC chain overlaps the TG mode,these two modes coupled each other and form the so called hybrid modes.The hybrid modes cover a larger bandwidth than that of the vacuum case,By adjusting the beam parameters,the space charge line will intersect with the hybrid mode,the intersection region are enlarged instead of a point,so the beam and the wave can maintain the phase in step in a large range,thus the "warm" bandwidth is expanded too.It should be noted that when operating at the hybrid modes,the coupled impedance is increased 3-5 times approximately larger than that of the vacuum case.Totally speaking,the slow wave characteristics are improved substantially due to the formation of the hybrid wave.2.The uniform self-consistent working equations of interaction between slow electromagnetic traveling wave and electron beam have been obtain,using the theory of mode expansion.The equations include excited equation,motion equation,phase evolving equation,etc.which are the basic equations that are used for studying nonlinear beam-wave interaction characteristics.3.The potential energy equation in space charge field was derived,By using variable-separated theory.Referring charged disc model from TianBingGeng,the space-charge field in vacuum and filled with plasma were analyzed using Green's function.The plasma satisfied the common static potential energy equation since the anisotropy of the plasma.The solving method of the common static potential energy equations is indicated in the paper.The space charge field has the essence distinction in the vacuum and the electric channel with plasma-back ground.The space charge field in the vacuum is decreased under the exponential trend,but the space charge field in the plasma is oscillation form and propagating faraway.That is why it is totally different of the beam-wave interaction affection in the plasma-background and vacuum-background.4.Using method of four-rank Runge-kutta,the big signal characteristic analysis code was compiled by MATLAB.It is shown that more than 35 percent of the efficiency will be achieved that more than CCTWT in vacuum-background.At the same time,the change of efficiency,power and gain when considering space charge field or not is also be analyzed,we find when space charge field is taken into account,the efficiency can be increased and the saturation length can be shortened.Nevertheless when space charge field is taken into account,the saturation length lengthened and the efficiency decreased in the vacuum-back ground.The contrary phenomena mean an essential distinction. Finally,the big signal characteristic of beam-wave interactive was analyzed when input power and density of plasma-background was different,the analysis result indicates that input power have little effect on output power.The efficiency will increase when the density of plasma increased.But when the density reached to a certain value,the efficiency will decrease when the density of the plasma increased.The reason is the range of overlap frequency between hybrid mode 2 and 3 will increase when density of plasma-background increases.Under the condition of the same input frequency,the best beam-wave synchronization condition is not satisfied,so the efficiency will decrease in contrast.