69 research outputs found
Kinetic Solvers with Adaptive Mesh in Phase Space
An Adaptive Mesh in Phase Space (AMPS) methodology has been developed for
solving multi-dimensional kinetic equations by the discrete velocity method. A
Cartesian mesh for both configuration (r) and velocity (v) spaces is produced
using a tree of trees data structure. The mesh in r-space is automatically
generated around embedded boundaries and dynamically adapted to local solution
properties. The mesh in v-space is created on-the-fly for each cell in r-space.
Mappings between neighboring v-space trees implemented for the advection
operator in configuration space. We have developed new algorithms for solving
the full Boltzmann and linear Boltzmann equations with AMPS. Several recent
innovations were used to calculate the discrete Boltzmann collision integral
with dynamically adaptive mesh in velocity space: importance sampling,
multi-point projection method, and the variance reduction method. We have
developed an efficient algorithm for calculating the linear Boltzmann collision
integral for elastic and inelastic collisions in a Lorentz gas. New AMPS
technique has been demonstrated for simulations of hypersonic rarefied gas
flows, ion and electron kinetics in weakly ionized plasma, radiation and light
particle transport through thin films, and electron streaming in
semiconductors. We have shown that AMPS allows minimizing the number of cells
in phase space to reduce computational cost and memory usage for solving
challenging kinetic problems
Ionization waves (striations) in low-current DC discharges in noble gases obtained with a hybrid kinetic-fluid model
A hybrid kinetic-fluid model is used to study ionization waves (striations)
in a low-current plasma column of DC discharges in noble gases. Coupled
solutions of a kinetic equation for electrons, a drift-diffusion equation of
ions, and a Poisson equation for the electric field are obtained to clarify the
nature of plasma stratification in the positive column and near-electrode
effects. A simplified two-level excitation-ionization model is used for the
conditions when the nonlinear effects due to stepwise ionization, gas heating,
and Coulomb interactions among electrons are negligible. It is confirmed that
the nonlocal effects are responsible for the formation of moving striations in
DC discharges at low plasma densities. The calculated properties of
self-excited waves of S, P, and R types in Neon and S type in Argon agree with
available experimental data. The reason for Helium plasma stability to
stratification is clarified. It is shown that sustaining stratified plasma is
more efficient than striation-free plasma when the ionization rate is a
nonlinear function of the electric field. However, the nonlinear dependence of
the ionization rate on the electric field is not required for plasma
stratification. Striations of S, P, and R types in Neon exist with minimal or
no ionization enhancement. Effects of the column length on the wave properties
have been demonstrated in our simulations
Peculiarities of charged particle kinetics in spherical plasma
We describe kinetic simulations of transient problems in partially ionized
weakly-collisional plasma around spherical bodies absorbing or emitting charged
particles. Numerical solutions of kinetic equations for electrons and ions in
1D2V phase space are coupled to an electrostatic solver using the Poisson
equation or quasineutrality condition for small Debye lengths. The formation of
particle groups and their contributions to electric current flow and screening
of charged bodies by plasma are discussed for applications to Langmuir probes
and solar wind
Power Consideration in the Pulsed Dielectric Barrier Discharge at Atmospheric Pressure
Nonequilibrium, atmospheric pressure discharges are rapidly becoming an important technological component in material processing applications. Amongst their attractive features is the ability to achieve enhanced gas phase chemistry without the need for elevated gas temperatures. To further enhance the plasma chemistry, pulsed operation with pulse widths in the nanoseconds range has been suggested. We report on a specially designed, dielectric barrier discharge based diffuse pulsed discharge and its electrical characteristics. Two current pulses corresponding to two consecutive discharges are generated per voltage pulse. The second discharge, which occurs at the falling edge of the voltage pulse, is induced by the charges stored on the electrode dielectric during the initial discharge. Therefore, the power supplied to ignite the first discharge is partly stored to later ignite a second discharge when the applied voltage decays. This process ultimately leads to a much improved power transfer to the plasma
Profiling and modeling of dc nitrogen microplasmas
This article explores electric current and field distributions in dc microplasmas, which have distinctive characteristics that are not evident at larger dimensions. These microplasmas, which are powered by coplanar thin-film metal electrodes with 400-μm minimum separations on a glass substrate, are potentially useful for microsystems in both sensing and microfabrication contexts. Experiments in N2N2 ambient show that electron current favors electrode separations of 4 mm at 1.2 Torr, reducing to 0.4 mm at 10 Torr. The glow region is confined directly above the cathode, and within 200–500 μm of its lateral edge. Voltage gradients of 100 kV/m exist in this glow region at 1.2 Torr, increasing to 500 kV/m at 6 Torr, far in excess of those observed in larger plasmas. Numerical simulations indicate that the microplasmas are highly nonquasineutral, with a large ion density proximate to the cathode, responsible for a dense space-charge region, and the strong electric fields in the glow region. It is responsible for the bulk of the ionization and has a bimodal electron energy distribution function, with a local peak at 420 eV. © 2003 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69877/2/JAPIAU-94-5-2845-1.pd
- …