Third-order transport coefficients for localised and delocalised charged-particle transport

We derive third order transport coefficients of skewness for a phase-space kinetic model that considers the processes of scattering collisions, trapping, detrapping and recombination losses. The resulting expression for the skewness tensor provides an extension to Fick's law which is in turn applied to yield a corresponding generalised advection-diffusion-skewness equation. A physical interpretation of trap-induced skewness is presented and used to describe an observed negative skewness due to traps. A relationship between skewness, diffusion, mobility and temperature is formed by analogy with Einstein's relation. Fractional transport is explored and its effects on the flux transport coefficients are also outlined.Comment: 11 pages, 3 figure

Third-order transport coefficients for electrons in N2 and CF4: effects of non-conservative collisions, concurrence with diffusion coefficients and contribution to the spatial profile of the swarm

Using a multi-term solution of the Boltzmann equation and Monte Carlo simulation technique we study behaviour of the third-order transport coefficients for electrons in model gases, including the ionisation model of Lucas and Saelee and modified Ness-Robson model of electron attachment, and in real gases, including N2 and CF4. We observe negative values in the E/n 0-profiles of the longitudinal and transverse third-order transport coefficients for electrons in CF4 (where E is the electric field and n 0 is the gas number density). While negative values of the longitudinal third-order transport coefficients are caused by the presence of rapidly increasing cross sections for vibrational excitations of CF4, the transverse third-order transport coefficient becomes negative over the E/n 0-values after the occurrence of negative differential conductivity. The discrepancy between the two-term approximation and the full multi-term solution of the Boltzmann equation is investigated for electrons in N2 and CF4. While the accuracy of the two-term approximation is sufficient to investigate the behaviour of the third-order transport coefficients in N2, it produces large errors and is not even qualitatively correct for electrons in CF4. The influence of implicit and explicit effects of electron attachment and ionisation on the third-order transport tensor is investigated. In particular, we discuss the effects of attachment heating and attachment cooling on the third-order transport coefficients for electrons in the modified Ness-Robson model, while the effects of ionisation are studied for electrons in the ionisation model of Lucas and Saelee, N2 and CF4. The concurrence between the third-order transport coefficients and the components of the diffusion tensor, and the contribution of the longitudinal component of the third-order transport tensor to the spatial profile of the swarm are also investigated. For electrons in CF4 and CH4, we found that the contribution of the component of the third-order transport tensor to the spatial profile of the swarm between approximately 50 Td and 700 Td, is almost identical to the corresponding contribution for electrons in N2. This suggests that the recent measurements of third-order transport coefficients for electrons in N2 may be extended and generalized to other gases, such as CF4 and CH4

Nove vrste riba i rakova u Crnogorskim vodama (južni Jadran)

The structure and composition of Mediterranean biodiversity has changed significantly. So far, in Montenegrin coastal waters, nine new non-native species have been recorded: Tylosurus acus imperialis, Caranx crysos, Siganus luridus, Fistularia commersonii, Stephanolepis diaspros, Sphoeroides pachygaster, Lagocephalus sceleratus, Callinectes sapidus and Farfantepanaeus aztecus. Allochthonous species are starting to compete for food and space and leading to habitat degradation, socio-economic impacts and can hybridise with the native species. Natural factors and human activities have enabled the arrival of non-native species into the Adriatic Sea. Four of the species are Lessepsian immigrants, which arrived via the Suez Canal, but five others were introduced from the Atlantic Ocean, through the Strait of Gibraltar. Analysis using the Marine Fish Invasiveness Screening Kit (MFISK), Aquatic Invasiveness Screening Kit (AS-ISK) and Receiver operating characteristic (ROC) showed a calibration threshold of 22.5 for MFISK, a BRA (Basic Risk Assessment) score of 34 and a CCA (Climate Change Assessment) score of 46. A measure of the accuracy of the calibration analysis is the area under the ROC curve (AUC). Two species were characterised as non-invasive: Tylosurus acus imperialis and Caranx crysos, but five others were characterised as invasive and covered by the categories from moderate to high-risk.Struktura i sastav bioraznolikosti Sredozemlja značajno su se promijenili. Do sada je u crnogor- skom primorju zabilježeno devet novih ne-nativnih vrsta: Tylosurus acus imperialis, Caranx crysos, Siganus luridus, Fistularia commersonii, Stephanolepis diaspros, Sphoeroides pachygaster, Lagocephalus sceleratus, Callinectes sapidus i Farfantepanaeus aztecus. Alohtone vrste počinju se natjecati za hranu i prostor i dovode do degradacije staništa, socio-ekonomskih učinaka i mogu hibridizirati s autohtonim vrstama. Prirodni čimbenici i ljudske aktivnosti omogućili su dolazak ne- nativnih vrsta u Jadransko more. Četiri vrste su lesepsijski imigranti, koji su stigli preko Sueskog kanala, ali pet drugih uneseno je iz Atlantskog oceana, kroz Gibraltarski tjesnac. Analiza korištenjem programa MFISK (Marine Fish Invasiveness Screening Kit), AS-ISK (Aquatic Invasiveness Screen- ing Kit) i ROC (Receiver operating characteristic) pokazala je prag kalibracije od 22,5 za MFISK, BRA (Basic Risk Assessment)) rezultat od 34 i CCA (Climate Change Assessment) ocjenu od 46. Mjera točnosti kalibracijske analize je površina ispod ROC krivulje (AUC). Dvije vrste okarakter- izirane su kao neinvazivne: Tylosurus acus imperialis i Caranx crysos, no pet drugih okarakter- izirano je kao invazivno i obuhvaćeno kategorijama od umjerenog do visokog rizika

Foundations and interpretations of the pulsed-Townsend experiment

The pulsed-Townsend (PT) experiment is a well known swarm technique used to measure transport properties from a current in an external circuit, the analysis of which is based on the governing equation of continuity. In this paper, the Brambring representation (1964 Z. Phys. 179 532) of the equation of continuity often used to analyse the PT experiment, is shown to be fundamentally flawed when non-conservative processes are operative. The Brambring representation of the continuity equation is not derivable from Boltzmann's equation and consequently transport properties defined within the framework are not clearly representable in terms of the phase-space distribution function. We present a re-analysis of the PT experiment in terms of the standard diffusion equation which has firm kinetic theory foundations, furnishing an expression for the current measured by the PT experiment in terms of the universal bulk transport coefficients (net ionisation rate, bulk drift velocity and bulk longitudinal diffusion coefficient). Furthermore, a relationship between the transport properties previously extracted from the PT experiment using the Brambring representation, and the universal bulk transport coefficients is presented. The validity of the relationship is tested for two gases Ar and SF6, highlighting also estimates of the differences

Kinetic and fluid models of non-equilibrium transport of electrons in gases and liquids

Ova doktorska disertacija sadrži dve celine. U prvoj celini su proučavani transportni koefi- cijenti trećeg reda za rojeve naelektrisanih čestica u gasovima. Struktura transportnog tenzora trećeg reda u svim konfiguracijama električnog i magnetskog polja određena je primenom metoda grupnih projektora. Fizička interpretacija individualnih komponenti ovog tenzora je analizirana na osnovu fluks gradijentne relacije i generalisane difuzione jednačine. Zavisnost transportnih koeficijenata trećeg reda od redukovanog električnog polja i njihova osetljivost na elementarne sudarne procese ispitane su za veliki broj modelnih i realnih gasova u Monte Carlo simulacijama i na osnovu numeričkih rešenja Boltzmann-ove jednačine. U drugoj celini je razmatran transport elektrona u tečnom argonu, tečnom kriptonu i tečnom ksenonu primenom Monte Carlo simulacija. Proučavani su uticaji efekata koherentnog rasejanja i različitih načina za aproksimaciju neelastičnih sudara u tečnoj fazi na izračunate vrednosti transportnih koeficijentata u ovim tečnostima. Poseban akcenat je stavljen na proučavanje strukturno indukovane negativne diferencijalne provodnosti u tečnom ksenonu na osnovu prostorno razloženih karakteristika roja i funkcija raspodele elektrona. Transportni koeficijenti za rojeve elektrona u atomskim tečnostima su iskorišćeni kao ulazni podaci u 1.5-dimenzionom klasičnom fluidnom modelu prvog reda i u fluidnom modelu zasnovanom na razvoju izvornog člana u jednačini kontinuiteta po gradijentima koncentracije. Ovi fluidni modeli upotrebljeni su za ispitivanje tranzicije lavina elektrona u strimere i propagacije negativnih strimera u atomskim tečnostima visoke mobilnosti. Pored toga, na osnovu ovih modela je razmatrano na koji način različit tretman neelastičnih sudara, priroda transportnih koeficijenata i rekombinacija kvazislobodnih elektrona i pozitivnih šupljina utiču na dinamiku i osobine strimerske plazme.The present doctoral dissertation contains two parts. The first part deals with the study of the third-order transport coefficients of charged-particle swarms in gases. The structure of the third-order transport tensor has been determined by employing the group projector technique in all configurations of electric and magnetic fields. The physical interpretation of the individual components of this tensor has been analyzed by employing the flux gradient relation and the generalized diffusion equation. The variation of the third-order transport coefficients with the reduced electric field and their sensitivity to elementary scattering processes have been determined for a wide range of model and real gases by using Monte Carlo simulations and the numerical solutions of the Boltzmann equation. The second part of this thesis deals with the transport of electrons in liquid argon, liquid krypton and liquid xenon by employing Monte Carlo simulations. The sensitivity of the calculated values of the transport properties in these liquids to coherent scattering effects and different approximations of inelastic scattering in the liquid phase has been investigated. A special emphasis has been placed on the study of the kinetic phenomenon of negative differential conductivity in liquid xenon by using spatially resolved swarm data and electron energy distribution functions. Transport coefficients of electron swarms in atomic liquids are used as input data in 1.5 dimensional classical first order fluid model, as well as in the fluid model which is based on the density gradient expansion of the source term in the equation of continuity. Both fluid models are employed in investigating the transition of electron avalanches into streamers and the propagation of negative streamers in high-mobility atomic liquids. In addition, the presented models are used for investigating how the dynamics and properties of the streamer plasma are influenced by the different treatment of inelastic collisions, nature of transport coefficients and the recombination of quasi-free electrons and positive holes

Electron transport in mercury vapor: cross sections, pressure and temperature dependence of transport coefficients and NDC effects

In this work we propose a complete and consistent set of cross sections for electron scattering in mercury vapor. The set is validated through a series of comparisons between swarm data calculated using a multi term theory for solving the Boltzmann equation and Monte Carlo simulations, and the available experimental data. Other sets of cross sections for electron scattering in mercury vapor were also used as input in our numerical codes with the aim of testing their completeness, consistency and accuracy. The calculated swarm parameters are compared with measurements in order to assess the quality of the cross sections in providing data for plasma modeling. In particular, we discuss the dependence of transport coefficients on the pressure and temperature of mercury vapor, and the occurrence of negative differential conductivity (NDC) in the limit of lower values of E∕N. We have shown that the phenomenon of NDC is induced by the presence of mercury dimers and that can be controlled by varying either pressure or temperature of mercury vapor. The effective inelastic cross section for mercury dimers is estimated for a range of pressures and temperatures. It is shown that the measured and calculated drift velocities agree very well only if the effective inelastic cross section for mercury dimers and thermal motion of mercury atoms are carefully considered and implemented in numerical calculations

Third-order transport coefficient tensor of electron swarms in noble gases

In this work we extend a multi term solution of the Boltzmann equation for electrons in neutral gases to consider the third-order transport coefficient tensor. Calculations of the third-order transport coefficients have been carried out for electrons in noble gases, including helium (He), neon (Ne), argon (Ar), krypton (Kr) and xenon (Xe) as a function of the reduced electric field, E/n0 (where E is the electric field while n0 is the gas number density). Three fundamental issues are considered: (i) the correlation between the longitudinal component of the third-order transport tensor and the longitudinal component of the diffusion tensor, (ii) the influence of the third-order transport coefficients on the spatial profile of electron swarm, and (iii) the errors associated with the two term approximation for calculating the third-order transport coefficients for electron swarms in noble gases. It is found that a very strong correlation exists between the longitudinal components of the third-order transport coefficient tensor and diffusion tensor for the higher values of E/n0. The effects of the third-order transport coefficients on the spatial profile of electron swarms are the most pronounced for noble gases with the Ramsauer-Townsend minimum in the cross sections for elastic scattering. The largest errors of two term approximation are observed in the off-diagonal elements of the third-order transport coefficient tensor in Ar, Kr and Xe for the higher values of E/n0