Interaction between low-pressure Ar–Hg plasma tubes and electromagnetic waves: Two-dimensional electromagnetic particle-in-cell simulation

This study integrates experiments and electromagnetic particle-in-cell (EM-PIC) simulations to investigate wave-plasma interactions in the 1–9 GHz band using non-uniform Ar-Hg plasma arrays. Two-dimensional plasma density distributions reconstructed from optical emission spectroscopy and double Langmuir probe measurements serve as inputs to the EM-PIC model. The simulation results agree well with experimental measurements, with mean absolute error and root mean square error both below 1 dB. A frequency–density dual-mode coupling is observed in both uniform and non-uniform plasmas: low-frequency waves attenuate more in low-density regions, while high-frequency waves are more effectively absorbed in high-density plasmas. Non-uniform plasmas enhance energy absorption through improved impedance matching, gradient-induced refraction/reflection, and resonant dissipation. This work provides a validated high-fidelity numerical tool for predicting electromagnetic wave attenuation in non-uniform plasmas and offers insights into the underlying physics of wave-plasma interactions in gradient media.