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

The creation and diagnosis of plasmas in high power microwave devices remains one of the primary challenges of plasma microwave electronics. In the present work we deal with (a) diagnostics techniques for characterization of radially nonuniform plasma columns suitable for use in high power microwave sources and (b) 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. The frequency shifts of the TM01n 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 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.