MCPlas, a MATLAB toolbox for reproducible plasma modelling with COMSOL

The MCPlas toolbox represents a collection of MATLAB functions for the automated generation of an equation-based fluid-Poisson model for non-thermal plasmas in the multiphysics simulation software COMSOL. Following the development of the new generation of the LXCat platform, all input data are prepared in a structured and interoperable JSON format and can be supplied and validated using existing JSON schemas. The toolbox includes fully transparent, editable MATLAB source code and offers an advanced description of electron transport in addition to commonly used approaches in the plasma modelling community. It supports one-dimensional and two-dimensional modelling geometries employing Cartesian, polar and cylindrical coordinate systems. MCPlas is tested on two reference cases: DC- and RF-driven low-pressure glow discharges in argon. Comparison of MCPlas results with results obtained by employing COMSOL’s Plasma Module verifies the reliability of the plasma model implemented by MCPlas and demonstrates the significance of electron transport treatment and boundary conditions applied in the toolbox. Using the same examples, the easy handling of complex reaction kinetic models in MCPlas and the reusability of its JSON input data across different modelling platforms are illustrated. This demonstrates that MCPlas provides a transparent and reproducible workflow for the simulation of non-thermal plasmas using COMSOL.

💡 Research Summary

The paper introduces MCPlas, an open‑source MATLAB toolbox that automates the creation of equation‑based fluid‑Poisson models for low‑temperature, non‑thermal plasmas within the COMSOL Multiphysics environment. The authors identify three major shortcomings of existing commercial plasma‑modelling tools: (i) the governing equations, boundary conditions and reaction mechanisms are hidden in proprietary project files, limiting user flexibility; (ii) complex reaction kinetic models (RKMs) must be entered manually, which is error‑prone and hampers reproducibility; and (iii) there is no machine‑readable, community‑wide standard for plasma chemistry data, preventing easy exchange and reuse across different simulation platforms.

To address these issues, MCPlas adopts a fully JSON‑based workflow. All model‑defining information—species, states, charges, transport coefficients, reaction rate coefficients, source terms, geometry parameters, and numerical settings—is stored in structured JSON documents that are validated against schemas derived from the latest LXCat data model and the Plasma‑MDS metadata standard. This design aligns the toolbox with the FAIR (Findable, Accessible, Interoperable, Reusable) principles and enables the same input files to be used directly in other plasma‑simulation codes.

The core of MCPlas is a set of MATLAB scripts that parse the JSON files and, via COMSOL’s LiveLink™ for MATLAB, programmatically construct a COMSOL model using the General Equation Module. Consequently, the generated model is fully transparent: the user can inspect, modify, or extend the exact continuity equations for particle densities, the electron energy balance, the Poisson equation, and all associated boundary conditions. No reliance on COMSOL’s proprietary Plasma Module is required.

A distinctive feature of MCPlas is its support for three electron‑transport formulations. The conventional drift‑diffusion approximation (DDAc) uses separate mobility and diffusion coefficients for electrons and electron energy. A simplified version (DDA53) is also provided, which is widely used in the literature. The novel “DDAn” option implements a higher‑order drift‑diffusion model derived from a Legendre‑polynomial expansion of the electron velocity distribution function, incorporating momentum and energy dissipation frequencies (νe, ν̃e) and transport coefficients (ξ0, ξ2, ξ̃0, ξ̃2). This model has been shown in prior studies to improve accuracy at both low and atmospheric pressures, and MCPlas is the first toolbox to make it readily available to users.

Boundary conditions follow the comprehensive treatment of Hagelaar et al. (2015). For electrons, the normal flux at surfaces includes contributions from thermal motion, drift, secondary electron emission, and reflection, with user‑definable parameters such as the electron reflection coefficient (re), secondary emission coefficient (γ), and ion flux‑dependent terms. Heavy‑particle fluxes are treated analogously. The Poisson equation is closed by fixing the applied voltage on the powered electrode and grounding the opposite electrode.

The toolbox supports one‑dimensional (Cartesian or polar) and two‑dimensional (Cartesian or cylindrical) geometries, covering planar, coaxial, and more general configurations. Users specify geometry dimensions (gap, dielectric thickness, electrode radius/length) in the JSON files, and MCPlas automatically builds the corresponding COMSOL mesh and physics interfaces.

To validate the approach, the authors simulate two benchmark cases: a DC glow discharge and an RF glow discharge in argon at low pressure. Results from MCPlas are compared with those obtained using COMSOL’s built‑in Plasma Module. The comparison shows excellent agreement for basic plasma parameters (electron density profiles, electric potential, current–voltage characteristics) when the same transport model is used. Importantly, when the DDAn transport model is employed, the MCPlas predictions align more closely with experimental data than the standard DDAc implementation, highlighting the impact of advanced transport modeling.

Beyond verification, the authors demonstrate the reusability of the JSON input files by feeding them into a different plasma‑simulation tool (e.g., PLASIMO). The same discharge conditions are reproduced without any modification of the chemistry data, confirming the interoperability promised by the JSON‑centric design.

MCPlas is released under the permissive MIT license, with the source code hosted on GitHub (https://github.com/INP‑SDT/MCPlas). All MATLAB files are openly accessible, allowing users to adapt the toolbox to specific research needs, add new reaction sets, or implement alternative boundary conditions while preserving full reproducibility.

In conclusion, MCPlas provides a transparent, reproducible, and interoperable workflow for fluid‑Poisson plasma modeling in COMSOL. By standardizing input data, automating model generation, and offering advanced electron‑transport options, it overcomes key limitations of existing commercial tools and paves the way for more reliable, shareable plasma‑simulation studies across the low‑temperature plasma community.