LoKI-GM: a global model framework for plasma chemistry studies

Global (zero-dimensional or spatially averaged) models are widely employed to study complex chemistries in low-temperature plasmas (LTPs). By adopting a spatially average description of the plasma, they substantially reduce the computational cost while still providing reliable and detailed insight into the key processes taking place in the plasma. In their most general formulation, global models involve the coupled solution of a Boltzmann solver (to describe the electron kinetics) and a Chemistry solver (to describe the heavy-species kinetics). This paper presents a tutorial on the LisbOn Kinetics Global Model (LoKI-GM) framework, developed in MATLAB and available as open-source code. The framework couples the Boltzmann solver LoKI-B, which solves the space-independent form of the two-term electron Boltzmann equation for non-magnetised non-equilibrium LTPs, excited by DC/HF electric fields or time-dependent (non-oscillatory) electric fields, and the Chemistry solver LoKI-C, which solves the system of zero-dimensional rate balance equations for the main charged and neutral species in the plasma and at the surface, receiving as input the kinetic schemes for the gas/plasma/surface system under study. Distinctive features of LoKI-GM include the closure of the model through charge neutrality, which yields the self-consistent maintenance field of DC and HF discharges, and the availability of several transport models for charged and neutral species. LoKI-GM can also couple a microkinetic mesoscopic surface model and a gas thermal model to the volume kinetics. We briefly present the formulation of LoKI-GM, including its numerical solution strategy, input/output parameters, and calculation workflow for both active discharges and afterglow plasmas. The main differences with respect to existing global models are highlighted, and the flexibility of the code for plasma chemistry studies is demonstrated through representative simulation results obtained across a range of gas discharge configurations and operating conditions.