Momentum transfer theory of nonconservative charged particle transport in mixtures of gases: General equations and negative differential conductivity

Negative mobility, sliding, and delocalization for stochastic networks

We consider prototype configurations for quasi-one-dimensional stochastic networks that exhibit negative mobility, meaning that current decreases or even reversed as the bias is increased. We then explore the implications of disorder. In particular, we ask whether lower and upper bias thresholds restrict the possibility to witness nonzero current (sliding and antisliding transitions, respectively), and whether a delocalization effect manifests itself (crossover from over-damped to under-damped relaxation). In the latter context detailed analysis of the relaxation spectrum as a function of the bias is provided for both on-chain and off-chain disorder.

Third-order transport coefficient tensor of charged-particle swarms in electric and magnetic fields

Third-order transport coefficient tensor of charged-particle swarms in neutral gases in the presence of spatially uniform electric and magnetic fields is considered using a multiterm solution of Boltzmann's equation and Monte Carlo simulation technique. The structure of the third-order transport coefficient tensor and symmetries along its individual components in varying configurations of electric and magnetic fields are addressed using a group projector technique and through symmetry considerations of the Boltzmann equation. In addition, we focus upon the physical interpretation of the third-order transport coefficient tensor by considering the extended diffusion equation which incorporates the contribution of the third-order transport coefficients to the density profile of charged particles. Numerical calculations are carried out for electron and ion swarms for a range of model gases with the aim of establishing accurate benchmarks for third-order transport coefficients. The effects of ion to neutral-particle mass ratio are also examined. The errors of the two-term approximation for solving the Boltzmann equation and limitations of previous treatments of the high-order charged-particle transport properties are also highlighted.

Microscopic theory for negative differential mobility in crowded environments

We study the behavior of the stationary velocity of a driven particle in an environment of mobile hard-core obstacles. Based on a lattice gas model, we demonstrate analytically that the drift velocity can exhibit a nonmonotonic dependence on the applied force, and show quantitatively that such negative differential mobility (NDM), observed in various physical contexts, is controlled by both the density and diffusion time scale of the obstacles. Our study unifies recent numerical and analytical results obtained in specific regimes, and makes it possible to determine analytically the region of the full parameter space where NDM occurs. These results suggest that NDM could be a generic feature of biased (or active) transport in crowded environments.

Striated microdischarges in an asymmetric barrier discharge in argon at atmospheric pressure

The investigation of striated microdischarges in barrier discharges in argon at atmospheric pressure is reported. Microdischarges were investigated by means of electrical measurements correlated with intensified CCD camera imaging. The scaling law theory known from low-pressure glow discharge diagnostics was applied in order to describe and explain this phenomenon. The investigated microdischarge is characterized as a transient atmospheric-pressure glow discharge with a stratified column. It can be described by similarity parameters i/r≈0.13 A/cm, pr≈5 Torr cm, and 3<λ/r<5 with the current i, pressure p, interval of subsequent striations λ, and radius of the plasma channel r. An attempt to describe the mechanism of creation of a striated structure is given, based on an established model of the spatial electron relaxation.

The influence of F, F2 on kinetics of electrons in BF3

We present transport coefficients for electrons in mixtures of BF3 with its radicals (specifically F and F2) for ratios of the electric field to the gas number density E/N from 1 to 1000 Td (1 Td = 10-21 V m2). Our analysis of non-conservative collisions revealed a range of E/N where electron attachment to radicals significantly changes the electron kinetics compared to pure gaseous BF3. The results were obtained using simple solutions for Boltzmann?s equation and Monte Carlo simulation.

Positron kinetics in soft condensed matter

We outline a new kinetic theory for positrons in soft matter, which blends together cross sections for positrons scattering from single molecules, with the structure function of the medium as a whole. Numerical results are presented for positrons in liquid argon, where negative differential conductivity arises from both positron formation and the structure of the medium.

Terahertz emission from collapsing field domains during switching of a gallium arsenide bipolar transistor

Broadband pulsed THz emission with peak power in the sub-mW range has been observed experimentally during avalanche switching in a gallium arsenide bipolar junction transistor at room temperature, while significantly higher total generated power is predicted in simulations. The emission is attributed to very fast oscillations in the conductivity current across the switching channels, which appear as a result of temporal evolution of the field domains generated in highly dense electron-hole plasma. This plasma is formed in turn by powerful impact ionization in multiple field domains of ultrahigh amplitude.

Electron drift velocities in mixtures of helium and xenon and experimental verification of corrections to Blanc's law

Measurements of electron drift velocities were performed in pure Xe and He and in a number of mixtures ranging up to 70% of Xe. The data were obtained by using a pulsed Townsend technique over the density-normalized electric field strength E/N between 1 and 100 Td . Even for pure gases there are no data in the entire range covered here, and these data represent an extension of accurate drift velocities to higher E/N. A selection of well-established cross sections for low energies, which was extended to higher energies, led to a reasonably good agreement of the calculated transport coefficients with the available data. At the same time we have applied the standard (common E/N) Blanc's law and two forms of common mean energy (CME, due to Chiflykian) procedures. Blanc's law fails for most mixtures at low and moderate E/N, while the CME procedure is capable of following the experimental data for the mixtures much more closely, and even predicting the negative differential conductivity region when such effect does not exist for pure gases. Thus the present paper also represents an experimental test of procedures to correct the standard Blanc's law. Finally, we have used the data for two mixtures to obtain results for the third mixture and in all cases this procedure gave excellent results even though only the standard Blanc's law was used in the process.