Electromagnetic properties of corrugated and smooth waveguides filled with radially inhomogeneous plasma

Creation and diagnosis of plasma in microwave devices remains one of the primary challenges of plasma microwave electronics. In the present work we deal with (1) diagnostic techniques for characterization of radially nonuniform plasma columns suitable for use in high-power microwave sources and (2) the effects of such plasmas on the electromagnetic properties of finite length, spatially periodic slow wave structures. Experimental studies were performed both for a strong and a weak guiding magnetic field. Using a combination of a microwave resonator (X-band) and a Langmuir probe, both the plasma peak density and its transverse profile were measured in situ (prior to beam propagation). The frequency upshifts of the TM_01n modes in an open corrugated cavity were measured as a function of the background plasma density. The dispersion diagrams were reconstructed, for the first time, up to a peak plasma density of 10¹² cm^-3 . Frequency upshifts and “flattening” of the dispersion curves were observed for both strong and weak guiding magnetic fields. For plasma density above 5×10¹¹ cm^-3 the frequency upshifts are less than anticipated by theory