Dispersion properties of plasma-filled corrugated waveguides :: SPE RESST

Dispersion properties of plasma-filled corrugated waveguides

A universal dispersion equation for a plasma-filled (hybrid) corrugated waveguide with an arbitrary shape of corrugations has been obtained. Plasma in the extremely strong external magnetic field has been considered.

Numerical calculations of the dispersion properties have been performed (Figures 1 - 3) for the slow-wave structures of Cherenkov devices (BWO and TWT). For the BWO and the TWT, the slow-wave structures are in the form of the periodic waveguides with sinusoidal and rectangular corrugations, respectively.


а)	б)

Fig. 1. Cherenkov structures: a) BWO; b) TWT


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Fig. 2. Dispersion curves: a) BWO; b) TWT


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Fig. 3. Dependences of the mode frequencies on the plasma density: a) BWO; b) TWT

It has been shown that the plasma presence inside the slow-wave structures does not change qualitatively the behavior of the dispersion curves for electromagnetic modes, but induces their shift to higher frequencies. The frequency shift depends on the plasma density and is different for TM modes and hybrid modes. By choosing the optimal plasma density, it is possible to increase the distances between the resonant frequencies of the operating TM mode and the parasitic hybrid modes. Thus the best conditions can be imposed for selective suppression of the parasitic modes in Cherenkov oscillators and amplifiers.