Meta-analysis of CO2 conversion, energy efficiency, and other performance data of plasma-catalysis reactors with the open access PIONEER database

This paper brings the comparison of performances of CO2 conversion by plasma and plasma-assisted catalysis based on the data collected from literature in this field, organised in an open access online database. This tool is open to all users to carry out their own analyses, but also to contributors who wish to add their data to the database in order to improve the relevance of the comparisons made, and ultimately to improve the efficiency of CO2 conversion by plasma-catalysis. The creation of this database and database user interface is motivated by the fact that plasma-catalysis is a fast-growing field for all CO2 conversion processes, be it methanation, dry reforming of methane, methanolisation, or others. As a result of this rapid increase, there is a need for a set of standard procedures to rigorously compare performances of different systems. However, this is currently not possible because the fundamental mechanisms of plasma-catalysis are still too poorly understood to define these standard procedures. Fortunately however, the accumulated data within the CO2 plasma-catalysis community has become large enough to warrant so-called “big data” studies more familiar in the fields of medicine and the social sciences. To enable comparisons between multiple data sets and make future research more effective, this work proposes the first database on CO2 conversion performances by plasma-catalysis open to the whole community. This database has been initiated in the framework of a H2020 European project and is called the “PIONEER DataBase”. The database gathers a large amount of CO2 conversion performance data such as conversion rate, energy efficiency, and selectivity for numerous plasma sources coupled with or without a catalyst. Each data set is associated with metadata describing the gas mixture, the plasma source, the nature of the catalyst, and the form of coupling with the plasma. Beyond the database itself, a data extraction tool with direct visualisation features or advanced filtering functionalities has been developed and is available online to the public. The simple and fast visualisation of the state of the art puts new results into context, identifies literal gaps in data, and consequently points towards promising research routes. More advanced data extraction illustrates the impact that the database can have in the understanding of plasma-catalyst coupling. Lessons learned from the review of a large amount of literature during the setup of the database lead to best practice advice to increase comparability between future CO2 plasma-catalytic studies. Finally, the community is strongly encouraged to contribute to the database not only to increase the visibility of their data but also the relevance of the comparisons allowed by this tool

Influence of a target on the electric field profile in a kHz atmospheric pressure plasma jet with the full calculation of the Stark shifts

\u3cp\u3eThe electric field in the head of the plasma bullet (ionization wave) in a cold atmospheric pressure plasma jet is measured using the Stark polarization spectroscopy technique, a noninvasive method. The jet is driven by 1 μ s long voltage pulses at 6 kV amplitude and 5 kHz frequency, and a helium gas flow of 1.5 slm. Two helium lines (447.1 nm and 492.2 nm) are studied, from which the peak-to-peak wavelength difference between the allowed and forbidden band of the spectral lines is determined. The full derivation to obtain the electric field from this peak-to-peak difference is included in this paper. The electric field is determined both inside and outside the capillary of the jet, up to about 2 cm in the effluent of the jet. Measurements are performed on the freely expanding jet, but especially the influence is studied when a target is placed in front of the plasma jet. Targets with different properties are used: insulating (polyvinyl chloride, PVC), conducting (copper), liquid (distilled water and saline), and organic (chicken breast). It is found that a target changes the electric field of the plasma jet and thus changes the plasma itself. This change depends on the dielectric constant or conductivity of the target: a higher dielectric constant or higher conductivity yields a higher electric field. For a low dielectric constant ( ϵ r ≈ 3), the change in the electric field is negligible. Decreasing the distance between the target and the capillary to below 2 cm yields an increase in the electric field.\u3c/p\u3

Atmospheric pressure plasma jet in controlled atmosphere:electric fields and propagation dynamics

\u3cp\u3eWe investigate the influence of the surrounding gas on the behaviour of guided ionization waves by measuring the electric field, propagation dynamics and emission spectra of a kHz operated helium plasma jet in surrounding gases such as nitrogen, oxygen and dry air. The electric field measurements performed using an electro-optic BSO crystal and the amount of deposited charge on the dielectric surface were calculated. These measurements showed a unique growth profile of the surface discharge in each of these surrounding gases after the guided ionization waves reaches the dielectric surface. The branching of surface discharges is observed when the nitrogen was used as the surrounding gas. The surface discharge profile in dry air and oxygen was diffused without any branching and it is wider in oxygen. The speed of growth of the discharge on the surface also decreases in nitrogen compared to dry air and oxygen. The measurements of propagation dynamics showed that the velocity of guided ionization waves is higher in oxygen containing gases. The result of this study showed that the presence of oxygen in the surrounding gas has a significant effect on guided ionization waves. These effects are mainly due to the photoionization of oxygen in the surrounding gas and also the electron detachment from the anions formed from oxygen.\u3c/p\u3

Cold atmospheric pressure plasma jets - charge carried by plasma bullets

Cold atmospheric pressure plasma jets are re-searched for applications in surface modification, synthesis, sterilization, medicine. Partially due to the relative ease of constructing a plasma jet, a great amount of work has been published on jets in a va-riety of gases, using excitation in a wide frequency range and in several typical geometries. Most com-monly reported on are descriptions of discharge dy-namics, densities of various reactive species, fol-lowed by gas temperature measurements, imaging of flow fields, and rarely electron densities and associ-ated electric fields. The first reported measurement of the electric field associated with plasma bullets has been performed by using a spectroscopic technique and published in 2011 by Sretenovic ́ et al [1], fol

Atmospheric pressure plasma jets in Helium – the electric field and the charge delivered to a dielectric surface

The family of non-thermal atmospheric pressure discharges has been the focus of intense research of a large number of research groups in the last fifteen years, as they are easy and cheap to assemble and run, and exhibit properties that can be used in surface treatment or biological applications. In this discharge family the non-thermal atmospheric pressure plasma jet commands a good deal of attention.\u3cbr/\u3eThe mentioned applications all involve the presence of a surface (target for treatment) in the vicinity of the discharge, and it has been shown that in many cases the presence of the surface alters the properties of the discharge. There are many types of surfaces to consider, from metals, dielectrics, to liquid surfaces, and they all leave a different mark on the discharge properties. Still, most of the research has been done on plasma jets expanding freely into the open air. \u3cbr/\u3eThis paper reports on the electric field and charge measurements delivered to a dielectric surface by an atmospheric-pressure plasma jet working in the bullet mode in helium. Imaging will be presented alongside the measurements of charge, as it will be evident that the charge distribution on the dielectric surface will mirror the observations obtained by imaging. The central results contain the charge packed in one ionization wave leaving the capillary towards the target, around 20 pC. The associated electric fields vary between 3×105 and 6×105 V/m

Dielectric barrier discharge in air with a controllable spatial distribution : a tomographic investigation

A novel dielectric barrier discharge source with a controllable discharge distribution has been designed for operation in atmospheric air. A predictable distribution has been achieved through the design of the powered electrode and the dielectric barrier. Optical emission tomography is used to study the discharge distribution. The method and its applicability in studies of non-symmetric plasmas are discussed in the paper. The results show that a desired discharge distribution may be achieved through the manipulation of the electric field amplification by the powered electrode and it is found that the discharge shape resembles the field imposed at the powered electrode only. Together with the flexibility of the plasma source design, this can prove highly advantageous for the treatment of irregularly shaped surfaces in plasma medicine and plasma surface processing at atmospheric pressure

Investigation of neutral beam arc chamber failure during helium operations at DIII-D

The Neutral Beam system on the DIII-D tokamak consists of eight ion sources using the Common Long Pulse Source (CLPS) design. During helium operation, desired for research regarding the ITER pre-nuclear phase, it has been observed that the ion source arc chamber performance steadily deteriorates, eventually failing due to electrical breakdown across the insulation. This poster presents the details and preliminary results of an experimental effort to replicate the problem in a bench top ion source with similar plasma parameters. The initial aim of the experiment is to test the hypothesis that during helium operation there is increased tungsten evaporation and sputtering due to ion bombardment of the hot cathodes, leading to the deposition of filament material on the insulation and subsequent short circuits. Ultimately the aim of the experiment is to find methods to ameliorate the problems associated with helium operation at DIII-D

Charge transfer to a dielectric target by guided ionization waves using electric field measurements

\u3cp\u3eA kHz-operated atmospheric pressure plasma jet is investigated by measuring charge transferred to a dielectric electro-optic surface (BSO crystal) allowing for the measurement of electric field by exploiting the Pockels effect. The electric field values, distribution of the surface discharge and amount of deposited charge are obtained for various parameters, including gas flow, applied voltage, target distance and the length of the capillary from ground to the end. A newly formed surface discharge emerges at the target when enough charge is deposited at the impact point and electric fields are high enough, i.e. 200 pC and 9 ±2 kV cm\u3csup\u3e-1\u3c/sup\u3e. The maximum amount of charge transferred by a single ionization wave ('plasma bullet') is 350 ±40 pC. Due to the emerging new surface discharge behind the impact point, the total charge deposited on the surface of the dielectric target can increase up to 950 pC. The shape of the secondary discharge on the target is found to be mainly driven by gas flow, while the applied voltage allows us to utilize longer distances within the boundaries set by this gas mixing. Finally the ionization wave is found to lose charge along its propagation on the inner walls of the capillary. The loss is estimated to be approximately 7.5 pC mm\u3csup\u3e-1\u3c/sup\u3e of travel distance inside the capillary.\u3c/p\u3

Imaging axial and radial electric field components in dielectric targets under plasma exposure

\u3cp\u3eThis work presents new ways to investigate the individual electric field components in a dielectric target induced by a non thermal atmospheric pressure plasma jet. Mueller polarimetry is applied to investigate electro-optic crystals under exposure of guided ionization waves produced by a plasma jet. Three different cases are examined to visualize the different electric field components induced in the crystals by charges deposited on the surface by impact of the ionization waves. Investigating a Bi\u3csub\u3e12\u3c/sub\u3eSiO\u3csub\u3e20\u3c/sub\u3e (BSO) crystal at normal incidence allows measurement and visualization of the axial field, while if the crystal is examined at 45° both radial and axial electric field components are combined. For the first time, a Fe:LiNbO\u3csub\u3e3\u3c/sub\u3e (Felinbo) crystal is examined using Mueller polarimetry under influence of a plasma jet. In this case, exclusively the patterns and local values of the radial field are obtained and not the axial field. These unique imaging options in the target for the individual electric field components allow a new and more complete investigation of the dynamics of surface discharges on dielectric materials.\u3c/p\u3