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In recent years, the interest in nonthermal plasma dynamics has grown significantly, within both industry and research. This has been driven by the development of several novel cold plasma technologies across a wide range of different fields, for example, for plasma medicine, chemical processing, pollution control, and surface treatment. The optimization of these technologies relies heavily upon the understanding of gas discharge plasmas: their generation, electrical characteristics, and interaction with their surroundings. Moreover, the manifestation of nonthermal plasmas in the form of streamers is of high relevance and critical importance to high voltage insulation technology, and has further significance to geophysical research concerning atmospheric discharges. The present work describes the development of the StrAFE (Streamers on Adaptive Finite Elements) package, a dedicated Python library built atop the popular open-source FEniCS finite element software, designed with the objective to simplify and to automate the solution of ionization front models. The library features support for mesh adaptivity, distributed memory parallelism, and an intuitive programming interface, while providing an exceptionally high level of user configurability. This article presents the software implementation, describes its features, and presents several code verification studies performed within simple and complex domains. It is concluded that the numerical results gained from this open-source framework are comparable to other well-established software in terms of accuracy. Therefore, it further demonstrates the great potential for open-source software to make significant contributions to technologies involving nonthermal plasmas, ionization fronts, and gas discharges. INDEX TERMSNonthermal plasma, gas discharge plasma, finite element analysis, open-source software, streamer discharge, high voltage phenomena, transient ionization fronts NOMENCLATURE A. FINITE ELEMENT METHOD

Modelling the development of streamer discharges across gas-solid dielectric interfaces is of increasing importance to the power and pulsed power industries. Deeper understanding of the dynamics and morphology of fast ionisation fronts in gases and at gas-solid interfaces underpins insulation coordination and optimization in high voltage power and pulsed power systems. However, many physical mechanisms behind gas-solid flashover remain to be fully understood. In this work, an adaptive mesh drift diffusion solver implemented on the open-source finite element framework FEniCS is used to perform computational streamer modelling across gas-solid interfaces. In this study, we verify our implementation by performing studies under a published configuration of a positive streamer initiating and propagating along a flat dielectric surface in a 2D domain. FEn-iCS is proved fully capable of performing streamer simulations in complex gas-solid topologies, with our results providing further evidence of accelerated surface streamers and other observed effects under various initial seed positions, surface permittivity, and applied voltage magnitudes.

This article presents the theoretical analysis of composite electrical insulation, formed from layered dielectric materials and subjected to impulsive energization. One-dimensional planar and cylindrical geometries were considered, consisting of an arbitrary number of layers with arbitrary relative permittivity and electrical conductivity. Analytical solutions have been succesfully derived for the time-dependent electric field inside the i-th layer. To demonstrate the usage of the model under complex multilayer topologies where analytical solutions are nontrivial, the characteristics of a 20-layer graded composite under microsecond and sub-microsecond impulses were analyzed and validated against a finite-element solver. Results indicate that the transient electric field response under impulsive energization is strongly dependent on the interplay between the composite relaxation time constants and the characteristic timescales associated with the applied impulse. The model is a further development for the design and coordination of functionally graded materials (FGMs) and composite insulation for high voltage system design. This is particularly relevant under fast-rising impulsive conditions as often encountered in many pulsed power applications.

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