Sergey Pancheshnyi

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium is a worldwide consortium which federates atomic and molecular databases through an e-science infrastructure and an organisation to support this activity. About 90% of the inter-connected databases handle data that are used for the interpretation of astronomical spectra and for modelling in many fields of astrophysics. Recently the VAMDC Consortium has connected databases from the radiation damage and the plasma communities, as well as promoting the publication of data from Indian institutes. This paper describes how the VAMDC Consortium is organised for the optimal distribution of atomic and molecular data for scientific research. It is noted that the VAMDC Consortium strongly advocates that authors of research papers using data cite the original experimental and theoretical papers as well as the relevant databases.

Comparisons of sets of electron–neutral scattering cross sections and swarm parameters in noble gases: I. Argon

This paper describes work done in the context of the Gaseous Electronics Conference (GEC) Plasma Data Exchange Project (PDEP) as discussed in the preface to this cluster issue. The purposes of this paper and its companion papers are to compare sets of cross sections for electron scattering from ground-state noble gas atoms in the energy range from thermal to about 1xa0keV and to comment on their applicability for plasma modelling. To these ends, we present in this paper intercomparisons of the nine independently derived sets of cross sections for electron scattering from ground-state argon atoms that have been posted in databases on the LXCat open-access website (www.lxcat.laplace.univ-tlse.fr). We show electron transport, excitation and ionization coefficients (swarm parameters) calculated using these cross section data in Boltzmann solvers and we compare calculated values with measurements. For the most part, the cross section sets have been compiled by co-authors on this paper and appendices giving details about how the various cross sections datasets were compiled have been written by the individual co-authors. Additional appendices discuss our criteria for selection of experimental data to be included in the comparisons and give a brief overview of the methods used here for solving the Boltzmann equation.

Numerical simulation of filamentary discharges with parallel adaptive mesh refinement

Direct simulation of filamentary gas discharges like streamers or dielectric barrier micro-discharges requires the use of an adaptive mesh. The objective of this paper is to develop a strategy which can use a set of grids with suitable local refinements for the continuity equations and Poissons equation in 2D and 3D geometries with a high-order discretization. The advantages of this approach are presented with a filamentary discharge simulation in plane-plane geometry in nitrogen within the diffusion-drift approximation.

The finite volume method solution of the radiative transfer equation for photon transport in non-thermal gas discharges: application to the calculation of photoionization in streamer discharges

This paper presents the development of a direct accurate numerical method to solve the monochromatic radiative transfer equation (RTE) based on a finite volume method (FVM) and its application to the simulation of streamer propagation. The validity of the developed model is demonstrated by performing direct comparisons with results obtained using the classic integral model. Comparisons with approximate solutions of the RTE (Eddington and SP3 models) are also carried out. Specific validation comparisons are presented for an artificial source of radiation with a Gaussian shape. The reported results demonstrate that whatever the value of the absorption coefficient, the results obtained using the direct FVM are in excellent agreement with the reference integral model with a significantly reduced computation time. When the absorption coefficient is high enough, the Eddington and SP3 methods are as accurate and become faster than the FVM. However, when the absorption coefficient decreases, approximate methods become less accurate and more computationally expensive than the FVM. Then the direct finite volume and the SP3 models have been applied to the calculation of photoionization in a double-headed streamer at ground pressure. For high values of the absorption coefficient, positive and negative streamers calculated using the SP3 model and the FVM for the photoionization source term are in excellent agreement. As the value of the absorption coefficient decreases, discrepancies between the results obtained with the finite volume and the SP3 models increase, and these differences increase as the streamers advance. For low values of the absorption coefficient, the use of the SP3 model overestimates the electron density and underestimates the photoionization source term in both streamers in comparison with the FVM. As a consequence, for low values of the absorption coefficient, positive and negative streamers calculated using the SP3 model for the photoionization source term propagate more slowly than those calculated using the FVM.

X-ray triggered PD measurements in small sized spherical voids at the detection limit

Pulsed X-ray triggered PD measurements were introduced in electrical testing in order to eliminate the statistical time lag. Moreover it was shown recently that the PD mechanism in air filled voids in epoxy insulation does not change with respect to natural inception of PD. In this paper we address the question of the detection limit of this method concerning the void size. In the case of bisphenol A based epoxy, as used in real GIS spacer insulators, we find clear indication that air-filled voids can be reliably triggered to diameters down to 0.3mm. Below this limit, the deposited charge becomes small and approaches the detection limit of the PD system. Therefore we conclude that our method is not limited by the size of the void.

Simulation of breakdown in small confined volumes inside dielectrics for electrical ageing and diagnostics

The objective of the present work is to develop a self-consistent model of DC and AC discharges in small voids in insulating materials encompassing an improved description of processes linked to the dielectric itself. To this end, a one-dimensional fluid model based on transport equations for charge carriers coupled to Poissons equation for electric fields was constructed for dielectrics containing air-filled voids of various sizes. Electron emission from the dielectric surface at the dielectric-gas interface is either continuous or discrete and is supposed to depend on the electric field at the surface. For DC voltages we find that current pulses exist for a range of conditions. These are due to the rapid accumulation of positive charges at the interface in partial discharge events and their eventual neutralization by electrons injected from the cathode and moving in the bulk dielectric. In AC, the transport of charges inside the dielectric has little influence on the discharge dynamics in gas, and the emission properties at the interface determine the shape and repetition rate of the current pulses.