Simulations of electromagnetic effects in high frequency capacitively coupled discharges using the Darwin approximation

The Darwin approximation is investigated for its possible use in simulation of electromagnetic effects in large size, high frequency capacitively coupled discharges. The approximation is utilized within the framework of two different fluid models which are applied to typical cases showing pronounced standing wave and skin effects. With the first model it is demonstrated that Darwin approximation is valid for treatment of such effects in the range of parameters under consideration. The second approach, a reduced nonlinear Darwin approximation-based model, shows that the electromagnetic phenomena persist in a more realistic setting. The Darwin approximation offers a simple and efficient way of carrying out electromagnetic simulations as it removes the Courant condition plaguing explicit electromagnetic algorithms and can be implemented as a straightforward modification of electrostatic algorithms. The algorithm described here avoids iterative schemes needed for the divergence cleaning and represents a fast and efficient solver, which can be used in fluid and kinetic models for self-consistent description of technical plasmas exhibiting certain electromagnetic activity

Future studies on electron scattering; A renaissance

2014 is the centenary of the first announcement of the Franck-Hertz experiment [1], now regarded as one of the pivotal experiments of modern physics. The Franck-Hertz experiment is widely regarded as an experiment that provided validation of the Bohr theory of atomic structure, itself only published in 2013, however it should also be viewed as the first quantitative experiment in electron scattering and the birth of scientific study of atomic and molecular phenomena by collisions. Today we recognize that electron-atom and electron- molecule collisions are prevalent across nature, describing disparate phenomena whilst the exploitation of such collisions underpins many of the technologies upon which modern society relies. The centenary of the Franck-Hertz experiment is thus a suitable opportunity to review both our current knowledge of electron interactions and to consider the directions of future research. In this article I therefore aim to both review our current state of knowledge and look forward, proposing that recent advances are providing something of a renaissance to the field and are vital for emerging technologies as well as answering some of the greatest scientific challenges of the 21st century

The 2017 Plasma Roadmap: Low temperature plasma science and technology

Journal of Physics D: Applied Physics published the first Plasma Roadmap in 2012 consisting of the individual perspectives of 16 leading experts in the various sub-fields of low temperature plasma science and technology. The 2017 Plasma Roadmap is the first update of a planned series of periodic updates of the Plasma Roadmap. The continuously growing interdisciplinary nature of the low temperature plasma field and its equally broad range of applications are making it increasingly difficult to identify major challenges that encompass all of the many sub-fields and applications. This intellectual diversity is ultimately a strength of the field. The current state of the art for the 19 sub-fields addressed in this roadmap demonstrates the enviable track record of the low temperature plasma field in the development of plasmas as an enabling technology for a vast range of technologies that underpin our modern society. At the same time, the many important scientific and technological challenges shared in this roadmap show that the path forward is not only scientifically rich but has the potential to make wide and far reaching contributions to many societal challenges.I Adamovich et al 2017 J. Phys. D: Appl. Phys. 50 32300

Maternal Immunization with Pneumococcal Surface Protein A Protects against Pneumococcal Infections among Derived Offspring

Pathogen-specific antibody plays an important role in protection against pneumococcal carriage and infections. However, neonates and infants exhibit impaired innate and adaptive immune responses, which result in their high susceptibility to pneumococci. To protect neonates and infants against pneumococcal infection it is important to elicit specific protective immune responses at very young ages. In this study, we investigated the protective immunity against pneumococcal carriage, pneumonia, and sepsis induced by maternal immunization with pneumococcal surface protein A (PspA). Mother mice were intranasally immunized with recombinant PspA (rPspA) and cholera toxin B subunit (CTB) prior to being mated. Anti-PspA specific IgG, predominantly IgG1, was present at a high level in the serum and milk of immunized mothers and in the sera of their pups. The pneumococcal densities in washed nasal tissues and in lung homogenate were significantly reduced in pups delivered from and/or breast-fed by PspA-immunized mothers. Survival after fatal systemic infections with various types of pneumococci was significantly extended in the pups, which had received anti-PspA antibody via the placenta or through their milk. The current findings strongly suggest that maternal immunization with PspA is an attractive strategy against pneumococcal infections during early childhood. (191 words

Enhanced control of the ionization rate in radio-frequency plasmas with structured electrodes via tailored voltage waveforms

International audienceRadio-frequency capacitively coupled plasmas that incorporate structured electrodes enable increases in the electron density within spatially localized regions through the hollow cathode effect (HCE). This enables enhanced control over the spatial profile of the plasma density, which is useful for several applications including materials processing, lighting and spacecraft propulsion. However, asymmetries in the powered and grounded electrode areas inherent to the hollow cathode geometry lead to the formation of a time averaged dc self-bias voltage at the powered electrode. This bias alters the energy and flux of secondary electrons leaving the surface of the cathode and consequentially can moderate the increased localized ionization afforded by the hollow cathode discharge. In this work, two-dimensional fluid-kinetic simulations are used to demonstrate control of the dc self-bias voltage in a dual-frequency driven (13.56, 27.12 MHz), hollow cathode enhanced, capacitively coupled argon plasma over the 66.6--200 Pa (0.5--1.5 Torr) pressure range. By varying the phase offset of the 27.12 MHz voltage waveform, the dc self-bias voltage varies by 10%--15% over an applied peak-to-peak voltage range of 600--1000 V, with lower voltages showing higher modulation. Resulting ionization rates due to secondary electrons within the hollow cathode cavity vary by a factor of 3 at constant voltage amplitude, demonstrating the ability to control plasma properties relevant for maintaining and enhancing the HCE

Plasma–liquid interactions: a review and roadmap

Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas