Electrical impedance of plasma filled waveguides in the MHz range

The Maxwell wave Equations have been numerically solved for the case of a cylindrical plasma-filed waveguide with perfectly conductive walls. The calculations have been done using the SPIREs code, which solves the electromagnetic propagation in frequency domain along the radius of the waveguide by means of a mixed spatial-spectral method (1D-space along radius, spectral domain along azimuthal and axial directions). The waveguide contains a column of plasma, magnetized along the axis of the cylinder, and an antenna, comprised in the gap between the plasma and the conducting wall. The antenna forces an oscillating current at radio-frequency in the Megahertz range. The electromagnetic response of the plasma is described by the Stix dielectric tensor plus the Fried-Conte Z dispersion function for finite-temperature Maxwellian effects. From the numerical solutions of the fields, the electrical impedance of the waveguides has been derived, and showed for a wide range of plasma parameters and waveguide radial sizes. The plasma density ranges from 10 ¹⁷ to 10 ²¹ particles/m ³, the magnetic field is below B < 0:1 Tesla, the frequencies are 13.56 and 27.12 (MHz), and the plasma cylinders have radius < 5 cm. The electrical resistance per unit length of the plasma is reported for each case. For a given geometry, the trends allow to find the maximum load conditions, corresponding to the maximum power coupling between the antenna and the plasma load. The results are relevant for many applications, ranging from the electrical design of the plasma-wave coupling in actual plasma devices, to the optimization of the RF plasma sources commonly used in industry. The method can also be proficiently applied to the design of high efficiency plasma sources used on board of spacecrafts for RF plasma thrusters.