2D Modeling of Plasma Discharge in Gas-Filled Capillary Using COMSOL Multiphysics

This work presents a two-dimensional (2D) axisymmetric model of a pulsed argon capillary discharge simulated in COMSOL Multiphysics. The model self-consistently couples the fluid plasma equations, Poisson’s equation, and an external resistor-inductor-capacitor (RLC) circuit to capture transient breakdown and non-equilibrium plasma formation driven by a high-voltage pulse. The model solves the coupled spatio-temporal dynamics of the discharge, providing temporal evolutions of the discharge current (for multiple applied voltages), electric potential, on-axis electron density, and reduced electric field, alongside axial spatial profiles of electron and ion densities, electron temperature, and reduced electric field. The results show that axial electron density increases with applied voltage, while the axial electron temperature profile is dominated by strong localized heating in the cathode fall region followed by sharp thermal relaxation in the plasma column. The predictive framework, previously validated against experimental data and now benchmarked against a reference numerical current profile, provides essential quantitative insights for characterizing key plasma properties and optimizing plasma control at emerging user facilities such as I-LUCE (INFN-Laser indUCEd Radiation Production) at INFN-LNS (Istituto Nazionale di Fisica Nucleare–Laboratori Nazionali del Sud), which aims to produce electron beams via laser wakefield acceleration (LWFA) using gas-filled capillaries for preclinical radiotherapy (RT) research.