Positron transport in water vapour

Transport properties of positron swarms in water vapour under the influence of electric and magnetic fields are investigated using a Monte Carlo simulation technique and a multi-term theory for solving the Boltzmann equation. Special attention is paid to the correct treatment of the non-conservative nature of positronium (Ps) formation and its explicit and implicit influences on various positron transport properties. Many interesting and atypical phenomena induced by these influences are identified and discussed. Calculated transport properties for positrons are compared with those for electrons, and the most important differences are highlighted. The significant impact of a magnetic field on non-conservative positron transport in a crossed field configuration is also investigated. In general, the mean energy and diffusion coefficients are lowered, while for the measurable drift velocity an unexpected phenomenon arises: for certain values of the reduced electric field, the magnetic field enhances the drift. The variation of transport coefficients with the reduced electric and magnetic fields is addressed using physical arguments with the goal of understanding the synergistic effects of Ps formation and magnetic field on the drift and diffusion of positrons in neutral gases

Spatiotemporal profile of emission from oscillating dc micro discharges

The axial light distributions in parallel-plate dc microdischarges in argon show similar behavior to large scale discharges. Between the low-current Townsend mode and the high current glow mode exists a large region of currents where different oscillations appear and the dynamic Volt-Ampere characteristic shows hysteresis behavior. During the oscillations the maximum peak intensity moves closer to the cathode, which is characteristic for the abnormal glow regime even though the average current is considerably smaller.Comment: submitted to: IEEE Trans. Plasma Sci., Spec. Issue on Images in Plasma Sc

Positron transport: the plasma-gas interface

Motivated by an increasing number of applications, new techniques in the analysis of electron transport have been developed over the past 30 years or so, but similar methods had yet to be applied to positrons. Recently, an in-depth look at positrontransport in pure argon gas has been performed using a recently established comprehensive set of cross sections and well-established Monte Carlo simulations. The key novelty as compared to electron transport is the effect of positronium formation which changes the number of particles and has a strong energy dependence. This coupled with spatial separation by energy of the positron swarm leads to counterintuitive behavior of some of the transport coefficients. Finally new results in how the presence of an applied magnetic field affects the transport coefficients are presented.This work was performed under MNTRS Project No. 141025

Plasma Induced DNA Damage: Comparison with the Effects Of Ionizing Radiation And Establishing Effective Treatment Doses

Atmospheric pressure plasma sources such as the plasma needle are being used for wound and chronic wound healing, cancer cell removal, stem cell manipulations, in dermatology, surgery, dentistry, etc. [1,2]. In our previous work we have optimized plasma needle parameters to efficiently sterilize E. Coli and S. Aureus in planktonic samples without causing damage to the peripheral blood mesenchymal stem cells used as a model for surrounding tissue [3]. Plasma treatments of human periodontal ligament mesenchymal stem cells have led to a promotion of osteogenic differentiation without affecting cell viability [4]. These results can be important for dentistry, especially for possible support or alternative to conventional regenerative procedures, such as guided tissue regeneration, the use of bone replacement grafts, and application of exogenous growth factors or proteins. Besides the promising short term effects of atmospheric non-thermal plasma on cells, it is necessary to study the long term effects, like for example DNA damage in order to prevent undesirable effects

Destruction of chemical warfare surrogates using a portable atmospheric pressure plasma jet

Today’s reality is connected with mitigation of threats from the new chemical and biological warfare agents. A novel investigation of cold plasmas in contact with liquids presented in this paper demonstrated that the chemically reactive environment produced by atmospheric pressure plasma jet (APPJ) is potentially capable of rapid destruction of chemical warfare agents in a broad spectrum. The decontamination of three different chemical warfare agent surrogates dissolved in liquid is investigated by using an easily transportable APPJ. The jet is powered by a kHz signal source connected to a low-voltage DC source and with He as working gas. The detailed investigation of electrical properties is performed for various plasmas at different distances from the sample. The measurements of plasma properties in situ are supported by the optical spectrometry measurements, whereas the high performance liquid chromatography measurements before and after the treatment of aqueous solutions of Malathion, Fenitrothion and Dimethyl Methylphosphonate. These solutions are used to evaluate destruction and its efficiency for specific neural agent simulants. The particular removal rates are found to be from 56% up to 96% during 10 min treatment. The data obtained provide basis to evaluate APPJ’s efficiency at different operating conditions. The presented results are promising and could be improved with different operating conditions and optimization of the decontamination process

Positron transport in molecular gases in crossed electric and\ud magnetic fields

Abstract. Transport properties of positron swarms drifting and diffusing in neutral gases under\ud the influence of crossed electric and magnetic fields are investigated using a multi-term theory\ud for solving the Boltzmann equation and Monte Carlo simulation technique. In the presence of\ud magnetic fields the number of transport properties is increased compared to the situation when\ud the positron swarm is acted on solely by an electric field. Since the longitudinal and transverse\ud components of the drift velocity show different sensitivities with respect to the strength of the\ud magnetic field, it is found that the negative differential conductivity effect in a crossed field\ud configuration can be controlled through the variation of the magnetic field strengths. Various\ud diffusion tensor elements also exhibit different sensitivities with respect to the magnetic field\ud and also with respect to the positronium (Ps) formation process

Electron excitation of neutral and ionic levels in Townsend discharges of argon at high E/N

We have measured the emission coefficients of the 3p levels of ArI: $3p_1$, $3p_5$, $3p_6$, $3p_7$, $3p_8$, and $3p_{10}$. The data for the $3p_5$, $3p_6$, $3p_7$, $3p_8$ and $3p_{10}$ levels were converted to excitation coefficients by using quenching coefficients from the literature. Measurements were performed in the range of E/N between $\rm 3 \times 10^{-20}\, Vm^2$ to above $\rm 5 \times 10^{-18}\, Vm^2$ except for the $3p_7$ level where measurements were done only up to $\rm 2\times 10^{-19}\, Vm^2$. The data for the emission coefficients for Ar II levels include two 4p' levels with terms ${}^2P^0_{1/2}$ and ${}^2F^0_{7/2}$, and three 4p levels with terms ${}^2P^0_{1/2}$, ${}^4P^0_{5/2}$ and ${}^2D^0_{5/2}$. The measurements for the ionic levels were done for E/N above $\rm 4\times 10^{-19}\, Vm^2$ up to nearly $\rm 1\times 10^{-17}\, Vm^2$. The absolute values of the coefficients were obtained from the intensity of the light emitted at the anode in the parallel plate self-sustained Townsend argon discharges. For low E/N the apparent emission coefficients (i.e. the normalized spatial profile of emission) for both neutral and ionic levels increase exponentially in almost the entire discharge gap. At about $\rm 5 \times 10^{-18}\, Vm^2$ the exponentially increasing signal was obtained only near the anode, while at $\rm 1\times 10^{-17}\,Vm^2$ the spatial dependence was flat throughout the electrode gap

LOW-PRESSURE DC DISCHARGE IN WATER VAPOUR

Abstract. We present investigations of low-pressure breakdown and different regimes of dc discharges in water vapour. Results of measurements include Paschen curves and VoltAmpere characteristics of the discharge for various pd conditions and with water samples of different purity

Axial emission profiles and apparent secondary electron yield in abnormal glow discharges in argon

This paper reports investigations of argon glow discharges established between flat disk electrodes, at pressure × electrode separation values between 45  and 150 . Parallel to the experimental studies the discharge is also described by a self-consistent hybrid model. The model uses as input data the measured electrical characteristics, this way making it possible to determine the apparent secondary electron emission coefficient. The model is verified through comparison of the measured and calculated spatial profiles of light emission, which are in good agreement for a wide range of conditions in the abnormal glow mode. Additionally, we investigate the dependence of the field reversal position on the discharge conditions and test the usual assumption that the position of the peak of emission closely coincides with the cathode fall – negative glow boundary.