Complex permittivity measurement in dielectric waveguide filled with argon plasma

An experimental set-up to measure the standing wave pattern of dielectric waveguide filled with low pressure plasma has been developed and is reported in this paper. Through the analysis of this pattern together with a solution of the complex algebra dispersion equation, a method is developed to determine the complex plasma permittivity that fills the dielectric waveguide. The experimental apparatus to measure the standing wave pattern of surface wave consists of a coaxial electric probe mounted in a moving carriage. The output signal of the probe is connected to a microwave detector and this output is a measurement of the relative electric field of the axial probe position around the dielectric waveguide. The microwave energy that sustains the plasma comes from a rectangular resonator excited by a quasi-CW magnetron. In the resonator there is a suitable pair of sleeves that launch the microwave energy stored in the dielectric waveguide. For 2.45 GHz and 750W of microwave power input a complex relative permittivity of (8.7-j15.8)×10^-3 is found.