Streamer propagation in the atmosphere of Titan and other N2:CH4 mixtures compared to N2:O2 mixtures

Streamers, thin, ionized plasma channels, form the early stages of lightning discharges. Here we approach the study of extraterrestrial lightning by studying the formation and propagation of streamer discharges in various nitrogen-methane and nitrogen-oxygen mixtures with levels of nitrogen from 20% to 98.4%. We present the friction force and breakdown fields Ek in various N2:O2 (Earth-like) and N2:CH4 (Titan-like) mixtures. The strength of the friction force is larger in N2:CH4 mixtures whereas the breakdown field in mixtures with methane is half as large as in mixtures with oxygen. We use a 2.5 dimensional Monte Carlo particle-in-cell code with cylindrical symmetry to simulate the development of electron avalanches from an initial electron-ion patch in ambient electric fields between 1.5Ek and 3Ek. We compare the electron density, the electric field, the front velocities as well as the occurrence of avalanche-to-streamer transition between mixtures with methane and with oxygen. Whereas we observe the formation of streamers in oxygen in all considered cases, we observe streamer inceptions in methane for small percentages of nitrogen or for large electric fields only. For large percentages of nitrogen or for small fields, ionization is not efficient enough to form a streamer channel within the length of the simulation domain. In oxygen, positive and negative streamers move faster for small percentages of nitrogen. In mixtures with methane, electron or streamer fronts move 10-100 times slower than in mixtures with oxygen; the higher the percentage of methane, the faster the fronts move.Comment: 34 pages, 11 figures, 1 tabl

Ab-initio electron scattering cross-sections and transport in liquid xenon

Ab-initio electron - liquid phase xenon fully differential cross-sections for electrons scattering in liquid xenon are developed from a solution of the Dirac-Fock scattering equations, using a recently developed framework [1] which considers multipole polarizabilities, a non-local treatment of exchange, and screening and coherent scattering effects. A multi-term solution of Boltzmann's equation accounting for the full anisotropic nature of the differential cross-section is used to calculate transport properties of excess electrons in liquid xenon. The results were found to agree to within 25% of the measured mobilities and characteristic energies over the reduced field range of 10^{-4} to 1 Td. The accuracies are comparable to those achieved in the gas phase. A simple model, informed by highly accurate gas-phase cross-sections, is presented to transform highly accurate gas-phase cross-sections to improve the liquid cross-sections, which was found to enhance the accuracy of the transport coefficient calculations.Comment: 26 pages, 9 figures. arXiv admin note: text overlap with arXiv:1503.0037

Derivation and test of high order fluid model for streamer discharges

A high order fluid model for streamer dynamics is developed by closing the system after the 4th moment of the Boltzmann equation in local mean energy approximation. This is done by approximating the high order pressure tensor in the heat flux equation through the previous moments. Mathematical characteristics of the system is studied. Then planar ionization fronts for negative streamers in Nsub2 are simulated with the classical streamer model, MC-PIC particle model, and with the present higher order model

Electron transport data in N2-O2 streamer plasma discharges

A multi-term theory for solving the Boltzmann equation and a Monte Carlo simulation technique are used to investigate the electron transport in mixtures of molecular nitrogen and oxygen. We investigate the way in which the transport coefficients and spatially resolved transport data are influenced by the amount of O2 in the mixture. This study was initiated in order to obtain the transport data for input into the fluid models and fluid components of hybrid models of streamers and has resulted in a database of such transport data

High order fluid model for streamer discharges

A high order fluid model for streamer discharges is developed and used to investigate propagation of negative streamer fronts in N2 . Mo- mentum transfer theory is employed to evaluate the collision terms and close the system of moment/balance equations. The results of simulations are compared with those obtained by a PIC/MC method and by the classical first order fluid model based on the drif

Comparing plasma fluid models of different order for 1D streamer ionization fronts

We evaluate the performance of three plasma fluid models: the first order reaction-drift-diffusion model based on the local field approximation; the second order reaction-drift-diffusion model based on the local energy approximation and a recently developed high order fluid model by Dujko et al (2013 J. Phys. D 46 475202) We first review the fluid models: we briefly discuss their derivation, their underlying assumptions and the type of transport data they require. Then we compare these models to a particle-in-cell/Monte Carlo (PIC/MC) code, using a 1D test problem. The tests are performed in neon and nitrogen at standard temperature and pressure, over a wide range of reduced electric fields. For the fluid models, transport data generated by a multi-term Boltzmann solver are used. We analyze the observed differences in the model predictions and address some of the practical aspects when using these plasma fluid models

Working of Section 153A of the Income Tax Act, 1961: Resolving the Conflict between the Literal Rule of Interpretation and Harmonious Construction

This article ventures into the various interpretations given by the court for the execution of Section 153A of the Income Tax Act, 1961. It has forever been a conflict as to how the particular section has to be interpreted, in order to decide whether the items of regular assessment can be added back in the proceeding under section 153A, after the finalization of assessment. This article tries to decode the mixed opinions of the court with regard to whether it is the literal rule of interpretation or the rule of harmonious construction that would apply to interpret Section 153A. This issue has been dealt with by the authors by analysing the various tools of interpretation of statutes like Literal Rule of Interpretation, reading down of statute as a whole, Rule of Harmonious Construction of statute etc. and their application in various cases based on judicial dicta of the court of law. The authors, based on thorough analysis of Section 153A, based on the language of the provision and the interpretations attached to it by the Judiciary, have tried to resolve the conflict between the Literal rule of interpretation and harmonious construction

Electron swarm transport in THF and water mixtures

The transport coefficients of electrons in mixtures of gaseous water and tetrahydrofuran (THF) are calculated using a multi-term solution of the Boltzmann equation. Electron transport coefficients at room temperature are presented over a range of reduced electric fields from 0.1–1000 Td, with significant differences between the behaviour in pure water and pure THF being found. The influence of the water to THF mixture ratio on the calculated transport coefficients is also presented