132 research outputs found
Nonlinear magnetoplasmons in strongly coupled Yukawa plasmas
The existence of plasma oscillations at multiples of the magnetoplasmon
frequency in a strongly coupled two-dimensional magnetized Yukawa plasma is
reported, based on extensive molecular dynamics simulations. These modes are
the analogues of Bernstein modes which are renormalized by strong interparticle
correlations. Their properties are theoretically explained by a dielectric
function incorporating the combined effect of a magnetic field, strong
correlations and finite temperature
Higher Harmonics Generation in Strongly Coupled Magnetized Two-Dimensional Yukawa Liquids
The excitation spectra of two-dimensional strongly coupled (liquid-like)
Yukawa systems under the influence of a magnetic field perpendicular to the
plane are found to sustain additional high-frequency modes at multiples of the
magnetoplasmon. These modes are reminiscent of the well-known Bernstein modes
but show a number of important differences due to the strong coupling of the
particles
Transport Coefficients of the Yukawa One Component Plasma
We present equilibrium molecular-dynamics computations of the thermal
conductivity and the two viscosities of the Yukawa one-component plasma. The
simulations were performed within periodic boundary conditions and Ewald sums
were implemented for the potentials, the forces, and for all the currents which
enter the Kubo formulas. For large values of the screening parameter, our
estimates of the shear viscosity and the thermal conductivity are in good
agreement with the predictions of the Chapman-Enskog theory.Comment: 11 pages, 2 figure
Kinetic simulation of the sheath dynamics in the intermediate radio-frequency regime
The dynamics of temporally modulated plasma boundary sheaths is studied in
the intermediate radio frequency regime where the applied radio frequency and
the ion plasma frequency are comparable. Two kinetic simulation codes are
employed and their results are compared. The first code is a realization of the
well-known scheme, Particle-In-Cell with Monte Carlo collisions (PIC/MCC) and
simulates the entire discharge, a planar radio frequency capacitively coupled
plasma (RF-CCP) with an additional heating source. The second code is based on
the recently published scheme Ensemble-in-Spacetime (EST); it resolves only the
sheath and requires the time resolved voltage across and the ion flux into the
sheath as input. Ion inertia causes a temporal asymmetry (hysteresis) of the
sheath charge-voltage relation; also other ion transit time effects are found.
The two codes are in good agreement, both with respect to the spatial and
temporal dynamics of the sheath and with respect to the ion energy
distributions at the electrodes. It is concluded that the EST scheme may serve
as an efficient post-processor for fluid or global simulations and for
measurements: It can rapidly and accurately calculate ion distribution
functions even when no genuine kinetic information is available
A scanning drift tube apparatus for spatio-temporal mapping of electron swarms
A "scanning" drift tube apparatus, capable of mapping of the spatio-temporal
evolution of electron swarms, developing between two plane electrodes under the
effect of a homogeneous electric field, is presented. The electron swarms are
initiated by photoelectron pulses and the temporal distributions of the
electron flux are recorded while the electrode gap length (at a fixed electric
field strength) is varied. Operation of the system is tested and verified with
argon gas, the measured data are used for the evaluation of the electron bulk
drift velocity. The experimental results for the space-time maps of the
electron swarms - presented here for the first time - also allow clear
observation of deviations from hydrodynamic transport. The swarm maps are also
reproduced by particle simulations
Collective excitations in electron-hole bilayers
We report a combined analytic and Molecular Dynamics analysis of the
collective mode spectrum of an electron-hole (bipolar) bilayer in the strong
coupling quasi-classical limit. A robust, isotropic energy gap is identified in
the out-of-phase spectra, generated by the combined effect of correlations and
of the excitation of the bound dipoles; the in-phase spectra exhibit a
correlation governed acoustic dispersion for the longitudinal and transverse
modes. Strong nonlinear generation of higher harmonics of the fundamental
dipole oscillation frequency and the transfer of harmonics between different
modes is observed. The mode dispersions in the liquid state are compared with
the phonon spectrum in the crystalline solid phase, reinforcing a coherent
physical picture.Comment: 4 pages, 5 figure
Kinetic Interpretation of Resonance Phenomena in Low Pressure Capacitively Coupled Radio Frequency Plasmas
The kinetic origin of resonance phenomena in capacitively coupled radio
frequency plasmas is discovered based on particle-based numerical simulations.
The analysis of the spatio-temporal distributions of plasma parameters such as
the densities of hot and cold electrons, as well as the conduction and
displacement currents reveals the mechanism of the formation of multiple
electron beams during sheath expansion. The interplay between highly energetic
beam electrons and low energetic bulk electrons is identified as the physical
origin of the excitation of harmonics in the current
Simulation benchmarks for low-pressure plasmas: capacitive discharges
Benchmarking is generally accepted as an important element in demonstrating the correctness of computer simulations. In the modern sense, a benchmark is a computer simulation result that has evidence of correctness, is accompanied by estimates of relevant errors, and which can thus be used as a basis for judging the accuracy and efficiency of other codes. In this paper, we present four benchmark cases related to capacitively coupled discharges. These benchmarks prescribe all relevant physical and numerical parameters. We have simulated the benchmark conditions using five independently developed particle-in-cell codes. We show that the results of these simulations are statistically indistinguishable, within bounds of uncertainty that we define. We therefore claim that the results of these simulations represent strong benchmarks, that can be used as a basis for evaluating the accuracy of other codes. These other codes could include other approaches than particle-in-cell simulations, where benchmarking could examine not just implementation accuracy and efficiency, but also the fidelity of different physical models, such as moment or hybrid models. We discuss an example of this kind in an appendix. Of course, the methodology that we have developed can also be readily extended to a suite of benchmarks with coverage of a wider range of physical and chemical phenomena
Breakdown in hydrogen and deuterium gases in static and radio-frequency fields
We report the results of a combined experimental and modeling study of the electrical breakdown of hydrogen and deuterium in static (DC) and radio-frequency (RF) (13.56 MHz) electric fields. For the simulations of the breakdown events, simplified models are used and only electrons are traced by Monte Carlo simulation. The experimental DC Paschen curve of hydrogen is used for the determination of the effective secondary electron emission coefficient. A very good agreement between the experimental and the calculated RF breakdown characteristics for hydrogen is found. For deuterium, on the other hand, presently available cross section sets do not allow a reproduction of RF breakdown characteristics
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