This work addresses plasma chemistry in the core of a vortex-stabilized microwave discharge for CO ₂ conversion numerically, focusing on the pressure-dependent contraction dynamics of this plasma. A zero-dimensional model is presented for experimental conditions in a pressure range between 60 and 300 mbar and a temperature range between 3000 and 6500 K. Monte Carlo flux (MCF) simulations, which describe electron kinetics, are self-consistently coupled to the plasma chemistry model. The simulation results show that an increase in pressure is accompanied by a transition in neutral composition in the plasma core: from a significant amount of CO ₂ and O ₂ at low pressures to a O/CO/C mixture at high pressures, the composition being determined mostly by thermal equilibrium and by transport processes. The change of temperature and composition with pressure lead to higher ionisation coefficient and more atomic ion composition in the plasma core. These changes result in an increase in ionisation degree in the plasma core from 10 ⁻⁵ to 10 ⁻⁴ . These factors are shown to be fundamental to drive contraction in the CO ₂ microwave discharge.

Global Models are widely used to study reaction kinetics in low-temperature plasma discharges. The governing conservative equations are simplified into a system of ordinary differential Equations in order to provide computationally feasible conditions to study complex chemistries with hundreds of species and thousands of reactions. This paper presents a detailed two-temperature global model for a H₂O-He mixture. The model developed in this work uses a statistical thermodynamics approach to solve the heavy particles energy equation self-consistently together with the electron energy and particles balance equations in order to improve the description of reactive plasma environments. Three analytical test cases are presented to validate and demonstrate the capability of this newly developed functionality embedded in PLASIMO software's \cite{Plasimo} global model module. The developed H₂O-He models are compared with the reported results for a radio-frequency plasma \cite{Liu2010_PSST} and then with experimental measured electron densities and gas temperature for a microwave induced plasma. In addition, conversion and energy efficiency of hydrogen and hydrogen peroxide productions are compared with experimental values (only for hydrogen) for a pure H₂O microwave induced plasma and with available literature results. This comparison underlines the challenges toward finding an optimal plasma configuration and conditions for production of hydrogen from water. The three analytical test cases for validation of the gas-temperature balance implementation in the PLASIMO global model and the detailed developed H₂O-He model can be used as benchmarks for other global plasma models. The PLASIMO input files for the presented H₂O-He model are available as supplementary materials; for any future update, please consult the PLASIMO website, https://plasimo.phys.tue.nl.

An ECRH (Electron Cyclotron Resonance Heating) system has been designed for JET in the framework of the JET Enhanced-Performance project (JET-EP) under the European Fusion Development Agreement (EFDA). Due to financial constraints it has recently been decided not to implement this project. Nevertheless, the design work conducted from April 2000 to January 2002 shows a number of features that can be relevant in preparation of future ECRH systems, e.g., for ITER.