We present and compare six simulation codes for positive streamer discharges from six different research groups. Four groups use a fully self-implemented code and two make use of COMSOL Multiphysics ®. Three test cases are considered, in which axisymmetric positive streamers are simulated in dry air at 1 bar and 300 K in an undervolted gap. All groups use the same fluid model with the same transport coefficients. The first test case includes a relatively high background density of electrons and ions without photoionization. When each group uses their standard grid resolution, results show considerable variation, particularly in the prediction of streamer velocities and maximal electric fields. However, for sufficiently fine grids good agreement is reached between several codes. The second test includes a lower background ionization density, and oscillations in the streamer properties, branching and numerical instabilities are observed. By using a finer grid spacing some groups were able to reach reasonable agreement in their results, without oscillations. The third test case includes photoionization, using both Luque's and Bourdon's Helmholtz approximation. The results agree reasonably well, and the numerical differences appear to be more significant than the type of Helmholtz approximation. Computing times, used hardware and numerical parameters are described for each code and test case. We provide detailed output in the supplementary data, so that other streamer codes can be compared to the results presented here.

This paper is mainly devoted to the comparison between the calculation and experimental results of primary and secondary streamer development in a point-to-plane positive corona discharge in dry air at atmospheric pressure. The qualitative agreement between experimental and calculation results based on the hydrodynamics approximation shows that the O radical is mainly produced in the secondary streamer which is in good agreement with the recent literature measurements using TALIF diagnostics. However, the O radical production yield (in terms of radicals produced per energy injected) is more efficient in the primary streamer than in the secondary one. The main positive corona discharge characteristics are revisited using fast electrical and optical ICCD and streak camera measurements. The calculation shows two streamer radii of, respectively, 10 µm (associated with the radial extension of a high electron density region) and 200 µm (corresponding to the extension of the radial space charge electric field).

A chemical kinetics model is developed to analyze the time evolution of the different main species involved in a flue gas initially stressed by a pulsed corona discharge at the atmospheric pressure and including N2, O2, H2O, and CO2 with a few ppm of NO. The present chemical kinetics model is coupled to a gas dynamics model used to analyze the radial expansion of the gas in the ionized channel created during the discharge phase. It is also meant to analyze the gas heating due to the Joule effect. This chemical kinetics model is also coupled to charged particle kinetics models based on a Boltzmann equation model to calculate the electron-molecule reaction coefficients in the flue gas and on a Monte Carlo code to estimate the energy and momentum transfer terms relative to ion-molecule collisions which are the input data for the gas dynamics model. It is shown, in particular, that the evolution of the radicals and the oxides is substantially affected by the gas temperature rise (from the initial value of 300 K up to 750 K near the anode) thus emphasizing the present coupling between gas dynamics, charged particle, and chemical kinetics models.

Two plasma devices at atmospheric pressure (air dielectric barrier discharge and helium plasma jet) have been used to study the early germination of Arabidopsis thaliana seeds during the first days. Then, plasma activated waters are used during the later stage of plant development and growth until 42 days. The effects on both testa and endospserm ruptures during the germination stage are significant in the case of air plasma due to its higher energy and efficiency of producing reactive oxygen species than the case of helium plasma. The latter has shown distinct effects only for testa rupture. Analysis of germination stimulations are based on specific stainings for reactive oxygen species production, peroxidase activity and also membrane permeability tests. Furthermore, scanning electron microscopy (SEM) has shown a smoother seed surface for air plasma treated seeds that can explain the plasma induced-germination. During the growth stage, plants were watered using 4 kinds of water (tap and deionized waters activated or not by the low temperature plasma jet). With regards to other water kinds, the characterization of the tap water has shown a larger conductivity, acidity and concentration of reactive nitrogen and oxygen species. Only the tap water activated by the plasma jet has shown a significant effect on the plant growth. This effect could be correlated to reactive nitrogen species such as nitrite/nitrate species present in plasma activated tap water.

This work is devoted to fluid modeling based on experimental investigations of a classical setup of a low-temperature plasma jet. The latter is generated at atmospheric pressure using a quartz tube of small diameter crossed by helium gas flow and surrounded by an electrode system powered by a mono-polar high-voltage pulse. The streamer-like behavior of the fast plasma bullets or ionization waves launched in ambient air for every high-voltage pulse, already emphasized in the literature from experimental or analytical considerations or recent preliminary fluid models, is confirmed by a numerical one-moment fluid model for the simulation of the ionization wave dynamics. The dominant interactions between electron and the main ions present in He-air mixtures with their associated basic data are taken into account. The gradual dilution of helium in air outside the tube along the axis is also considered using a gas hydrodynamics model based on the Navier-Stokes equation assuming a laminar flow. Due to the low magnitude of the reduced electric field E/N (not exceeding 15 Td), it is first shown that consideration of the stepwise ionization of helium metastables is required to reach the critical size of the electron avalanches in order to initiate the formation of ionization waves. It is also shown that a gas pre-ionization ahead of the wave front of about 10 9 cm −3 (coming from Penning ionization without considering the gas photo-ionization) is required for the propagation. Furthermore, the second ionization wave experimentally observed during the falling time of the voltage pulse, between the powered electrode and the tube exit, is correlated with the electric field increase inside the ionized channel in the whole region between the electrode and the tube exit. The propagation velocity and the distance traveled by the front of the ionization wave outside the tube in the downstream side are consistent with the present experimental measurements. In comparison with the streamer dynamics in a classical corona discharge, it is shown that under the same gas composition the plasma jet ionization waves propagate with a lower velocity (about 5 times), and have a higher diameter (at least 10 times) and a lower plasma density (at least 100 times).

This article concerns a new field covered by low-temperature plasmas at atmospheric pressure for medical treatments. This is based on the very attractive possibility to tune and design plasmas as possible pharmaceutical products using selectively some active species (charged particles, radicals, atomic and molecular agents, UV radiations) and even electric fields self-generated by the plasma. The delivery of active species occurs at the gaseous level. This means that there is no need for a carrier medium, and the treatment of living tissue or surface is optimal because plasmas can penetrate small pores, spread over rough surfaces, and reach both prokaryotic and eukaryotic cells. The present article gives first a review on the main low-temperature plasma setups potentially usable for medical treatments with an emphasis on the setups as, for instance, plasma jets developed in our laboratory. Then, the present article gives a review of the current state of the art of such plasmas as pharmaceutical products or therapeutic tools in medicine with a light on a selection of forefront researches particularly in the field of chronic wounds, blood coagulation, and cancer treatment.

Biomedical applications of low-temperature plasmas are of growing interest, especially in the field of plasma-induced anti-tumor effects. The present work is aimed at investigating the regionalized antiproliferative effects of low-temperature plasmas on a multicellular tumor spheroid (MCTS), a model that mimics the 3D organization and regionalization of a microtumor region. We report that a low-temperature plasma jet, using helium flow in open air, inhibits HCT116 colon carcinoma MCTS growth in a dose-dependent manner. This growth inhibition is associated with the loss of Ki67, and the regionalized accumulation of DNA damage detected by histone H2AX phosphorylation. This regionalized genotoxic effect leads to massive cell death and loss of the MCTS proliferative region. The use of reactive oxygen species (ROS), scavenger Nacetyl cysteine (NAC) and plasma-conditioned media demonstrate that the ROS generated in the media after exposure to low-temperature plasma play a major role in these observed effects. These findings strengthen the interest in the use of MCTS for the evaluation of antiproliferative strategies, and open new perspectives for studies dedicated to demonstrate the potential of low-temperature plasma in cancer therapy.Keywords: low temperature plasma, multi-cellular tumor spheroid, antiproliferative effect, genotoxic and cytotoxic effects, reactive oxygen species IntroductionIn the field of biomedical applications, low-temperature plasmas ejected in open air are an interesting source of active species (charged particles, radicals, long-lived excited species, UV photons, electric field, etc) that can easily be launched, for example, on any prokaryote or eukaryote cells, living tissues, biomaterial surfaces, etc. Such plasma species have been known for many years for their bactericide action useful in decontamination or sterilization [1], and also more recently for wound healing and cell regeneration [2], biomaterial functionalization [3], blood coagulation [4], and gene transfection [5]. The reader can find more exhaustive lists of references on these biomedical applications (for example, in [6][7][8]) and also on plasma-induced anti-tumor effects that are evocated, hereafter, in the light of a few examples of the literature.Indeed nowadays, there is a growing interest on research works devoted to the effect of low-temperature plasmas at atmospheric pressure on cancer cells, both in vitro and in vivo. Recent studies have shown, more particularly, a plasma-induced cell cycle arrest and activation of apoptosis in glioma and colorectal carcinoma HCT116 colon cancer cells [9,10], an activation of p53-dependent cell death in plasma-exposed HCT116 [11], and a mitochondriamediated apoptosis in the case of human cervical cancer HeLa cells [12]. It has also been suggested that the plasma effect could eradicate lung and/or murine melanoma cancer cells with reduced damaging effects on normal or fibroblast cells [13,14]. Finally, in vivo reduction of mice xenografted tumors from the bladder [13], glioma cells [10]...

An improved Monte Carlo method is developed for the simulation of the ion transport in classical drift tube in the case of ion-molecule asymmetric systems such as O−/O2 or N+/N2. The aim of this new method is to overcome the problem of incident ions which vanish at relative high electric field due to asymmetric charge transfer or electron detachment. These ion removal processes are compensated by a fictitious ion creation which improves the accuracy of the ion distribution function and swarm coefficient calculations. The classical ion-molecule collision processes occurring in weakly ionized gases at room temperature (elastic collisions including energy exchange and thermal motion of background gases and also inelastic collisions) are taken into account. This new method is then validated and the transport and reaction coefficients have been given for a large range of E/N (a part of them for the first time in the literature) in O−/O2 and N+/N2 systems.