Technologies based on non-equilibrium, low-temperature plasmas are ubiquitous in today’s society. Plasma modeling plays an essential role in their understanding, development and optimization. An accurate description of electron and ion collisions with neutrals and their transport is required to correctly describe plasma properties as a function of external parameters. LXCat is an open-access, web-based platform for storing, exchanging and manipulating data needed for modeling the electron and ion components of non-equilibrium, low-temperature plasmas. The data types supported by LXCat are electron- and ion-scattering cross-sections with neutrals (total and differential), interaction potentials, oscillator strengths, and electron- and ion-swarm/transport parameters. Online tools allow users to identify and compare the data through plotting routines, and use the data to generate swarm parameters and reaction rates with the integrated electron Boltzmann solver. In this review, the historical evolution of the project and some perspectives on its future are discussed together with a tutorial review for using data from LXCat.

This study details the development, validation, and utilization of a multi-term Boltzmann equation (BE) model to benchmark argon cross-section sets for their use in low temperature plasma models. First, a complete derivation of the multi-term BE model is given. The multi-term BE model is verified by comparing calculated transport coefficients to known solutions for both conservative and non-conservative model gases. A general comparison between the solutions of the multi-term BE model and the solutions of the two-term BE model, BOLSIG+ , and the Monte Carlo collision model, METHES, is also reported. The multi-term BE model is used to calculate electron swarm parameters from three independently developed argon cross-section sets, which are compared with experimental data. Swarm parameters calculated from the Biagi cross-section set feature the best agreement with experimental data, with the exception of the first Townsend coefficient, which is best reproduced using the cross-section set of Zatsarinny and Bartschat.

A laser-driven semiconductor switch (LDSS) employing silicon (Si) and gallium arsenide (GaAs) wafers has been used to produce nanosecond-scale pulses from a 3 μs, 110 GHz gyrotron at the megawatt power level. Photoconductivity was induced in the wafers using a 532 nm laser, which produced 6 ns, 230 mJ pulses. Irradiation of a single Si wafer by the laser produced 110 GHz RF pulses with a 9 ns width and >70% reflectance. Under the same conditions, a single GaAs wafer yielded 24 ns 110 GHz RF pulses with >78% reflectance. For both semiconductor materials, a higher value of reflectance was observed with increasing 110 GHz beam intensity. Using two active wafers, pulses of variable length down to 3 ns duration were created. The switch was tested at incident 110 GHz RF power levels up to 600 kW. A 1-D model is presented that agrees well with the experimentally observed temporal pulse shapes obtained with a single Si wafer. The LDSS has many potential uses in high power millimeter-wave research, including testing of high-gradient accelerator structures.

Two basic challenges limiting the simulation capabilities of the streamer discharge community are the efficient resolution of Poisson’s equation and the proper treatment of photoionization. This paper addresses both of these challenges, beginning with a graphics processing unit executed multigrid (MG) algorithm to efficiently solve Poisson’s equation on a massively parallel platform. When utilized in a 3D particle-in-cell (PIC) model with radiation transport, the MG solver is demonstrated to reduce the required simulation time by approximately a factor of three over a conventional Jacobi scheme. Next, a fully theoretical photoionization model, based on the basic properties of N ₂ and O ₂ molecules is developed as an alternative to widely utilized semi-empirical models. Following a review of N ₂ emission properties, a total of eight transitions from only three excited states are reported as a base set of transitions for a practical physics-based photoionization model. A 3D PIC simulation of streamer formation is demonstrated with two dominant transitions included in the radiation transport model.

Owing to its distinctive photon energy range, vacuum ultraviolet (VUV) emission plays a key role in diverse photo-induced natural and technological processes. Atmospheric-pressure plasma produced VUV is central to resolve long-held issues in dynamics of natural (e.g., lightning) and laboratory (e.g., streamer) plasmas. Challenging the seemingly unavoidable vacuum systems used to prevent VUV emission quenching by ambient gases, here we report the first observation of vacuum-free generation of stable sub-110 nm VUV emission from atmospheric-pressure plasmas jetted into open air and atmospheric air plasma. Emission from atomic helium at 58.4 nm is observed from a nonequilibrium atmospheric pressure plasma jet (N-APPJ), jetted directly into ambient air. In a similar experiment, we also report VUV emission from excited nitrogen species in an atmospheric pressure discharge in ambient air. The photon emissions detected expand the window of photo-induced processes beyond ∼10 eV commonly achievable by existing non-excimer VUV plasma sources, and enables direct photo-excitation and ionization of molecular species such as CO ₂ and many others. The thus-enabled direct photoionization of O ₂ , O, and N species further justifies the role of direct photoionization in the dynamics of natural and laboratory atmospheric-pressure plasmas and informs the development of the relevant plasma photoionization models, which currently largely sidestep the sub-110 nm domain. These findings can make contribution to the complement of photoionization model of lightning, streamer, and other plasmas, open new avenues to quantify the yet elusive role of photoionization in the plasma dynamics.