With The Center Conductor Axis Of Helical Groove Slow-wave System And Note - The Study Of Wave Interaction

As the key component of the beam-wave interaction of a Traveling Wave Tube (TWT) for exciting microwave energy, the slow-wave structure (SWS) basically determines the performance of the TWT. In this dissertation, we have made detailed theoretical study and numerical computing on some new types of helical groove SWS including the conductor-centered rectangle-shaped helical groove and the conductor-centered arbitrarily-shaped helical groove; Several important new conclusions and valuable results are achieved and listed as the followings:1. The research on the RF characteristics of the conductor-centered helical groove SWS.(a) In the 'cold ' system, we found that the changing of depth of the groove has no distinct effects on the phase velocity at the lower frequency region; but with the increasing of the frequency, the phase velocity and bandwidth are reduced slightly, the structure is more dispersive and the coupling impedance is enhanced. The increasing of the width of the groove makes the phase velocity decreased largely but almost no effects on the bandwidth, and the coupling impedance enhanced. With the radius of the center conductor increasing, the phase velocity is also decreased a lot, the bandwidth is relatively widened, and the dispersion of the structure is weakened but the coupling impedance is lowered.(b) The linear fluid model is used to study the conductor-centered helical groove TWT. We have analyzed the effects of the beam parameters on the gain and the bandwidth of the TWT. The results show that by increasing the beam current or beam radius, the gain of the structure can be increased. The decreasing of the beam voltage increases the gain of the TWT but reduces the bandwidth. The bandwidth of this kind of TWT can reach 30-40% if choosing the optimal parameters of the structure and the beam. And we also know the depth of the groove should not be too shallow; The width of the groove should be widened relatively, and the space of the interaction area should not be too narrow.2. For the first time we investigate detailedly on the theory of the conductor-centered arbitrarily-shaped helical groove structure. We divide the arbitrarily-shaped helical groove into many consecutive small rectangle area to approximate the original groove. The recurrence relation of the admittance is obtained. It can be used in the situations of both smooth boundary and discontinuous boundary.3. A theory for the analysis of the arbitrarily-shaped helical groove structure is obtained by means of an approximate field-theory. The dispersion equation and the coupling impedance expressions of the conductor-centered arbitrarily-shaped helical groove structure are presented for the first time; Based on these theories, the effects of the groove shape on RF characteristics of the structure are investigated by numerical calculation. The results show that:(a) The influence of the groove shape on the high cut-off frequency is great at certain groove depth; the high cut-off frequency is gradually lowered from triangle profile, cosine profile to swallow-tailed profile.(b) When the depth of the groove is relatively shallow, the helical triangle-shaped helical groove has the widest bandwidth, the least dispersion, and the fastest phase velocity.(c) For the helical swallow-tailed structures with same groove width, the deep groove depth one which is suitable for the use in a interaction system of high power TWTs, has the largest coupling impedance and the lowest phase velocity in comparison with the other different groove profiles.4. For the first time, the unified 'hot' dispersion equation which can be used to analyze structures with different groove profiles is obtained by means of an approximate self-consistent field-theory. The results of the following calculations show that we can get a structure with the best performance through choosing the optimal parameters.