32 research outputs found
Searching for order in atmospheric pressure plasma jets
The self-organized discharge behaviour occurring in a non-thermal radio-frequency plasma jet in rare gases at atmospheric pressure was investigated. The frequency of the azimuthal rotation of filaments in the active plasma volume and their inclination were measured along with the gas temperature under varying discharge conditions. The gas flow and heating were described theoretically by a three-dimensional hydrodynamic model. The rotation frequencies obtained by both methods qualitatively agree. The results demonstrate that the plasma filaments forming an inclination angle α with the axial gas velocity u z are forced to a transversal movement with the velocity , which is oriented in the inclination direction. Variations of in the model reveal that the observed dynamics minimizes the energy loss due to convective heat transfer by the gas flow. The control of the self-organization regime motivates the application of the plasma jet for precise and reproducible material processing
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Verified modeling of a low pressure hydrogen plasma generated by electron cyclotron resonance
A self-consistent fluid model has been successfully developed and employed to model an electron cyclotron resonance driven hydrogen plasma at low pressure. This model has enabled key insights to be made on the mutual interaction of microwave propagation, power density, plasma generation, and species transport at conditions where the critical plasma density is exceeded. The model has been verified by two experimental methods. Good agreement with the ion current density and floating potentialâas measured by a retarding energy field analyzerâand excellent agreement with the atomic hydrogen densityâas measured by two-photon absorption laser induced fluorescenceâenables a high level of confidence in the validity of the simulation
Non-local model of hollow cathode and glow discharge - theory calculations and experiment comparison
General form of the non-local equation for an ionization source in glow
discharge and hollow cathode 3D-simulation is formulated. It is a fundamental
equation in a hollow cathode theory, which allows to make up a complete set of
field equations for a self-consistent problem in a stationary glow discharge
and a hollow cathode. It enables to describe adequately the region of negative
glow and the hollow cathode effect. Here you can see first attempts to compare
calculation results of electrical dependences (pressure - voltage) and
experimental data, - under conditions of gradual appearance of the hollow
cathode effect.Comment: 4 pages, 2 figure
HelixJet : an innovative plasma source for nextâgeneration additive manufacturing (3D printing)
A novel plasma source (HelixJet) for use in additive manufacturing (AM)/3D printing is proposed. The HelixJet is a capacitively coupled radio frequency plasma with a doubleâhelix electrode configuration that generates a surprisingly stable and homogeneous glow plasma at low flow rates of argon and its mixtures at atmospheric pressure. The HelixJet was tested on three polyamide powders usually used to produce parts by laser sintering, a powderâbased AM process, to form local deposits. The chemical composition of such plasmaâprinted samples is compared with thermally produced and laserâsintered samples with respect to differences in morphology that result from the different thermal cycles on several length scales. Plasma prints exhibit unique features attributable to the nonequilibrium chemistry and to the highâspeed heat exchange
Markov Properties of Electrical Discharge Current Fluctuations in Plasma
Using the Markovian method, we study the stochastic nature of electrical
discharge current fluctuations in the Helium plasma. Sinusoidal trends are
extracted from the data set by the Fourier-Detrended Fluctuation analysis and
consequently cleaned data is retrieved. We determine the Markov time scale of
the detrended data set by using likelihood analysis. We also estimate the
Kramers-Moyal's coefficients of the discharge current fluctuations and derive
the corresponding Fokker-Planck equation. In addition, the obtained Langevin
equation enables us to reconstruct discharge time series with similar
statistical properties compared with the observed in the experiment. We also
provide an exact decomposition of temporal correlation function by using
Kramers-Moyal's coefficients. We show that for the stationary time series, the
two point temporal correlation function has an exponential decaying behavior
with a characteristic correlation time scale. Our results confirm that, there
is no definite relation between correlation and Markov time scales. However
both of them behave as monotonic increasing function of discharge current
intensity. Finally to complete our analysis, the multifractal behavior of
reconstructed time series using its Keramers-Moyal's coefficients and original
data set are investigated. Extended self similarity analysis demonstrates that
fluctuations in our experimental setup deviates from Kolmogorov (K41) theory
for fully developed turbulence regime.Comment: 25 pages, 9 figures and 4 tables. V3: Added comments, references,
figures and major correction
Particles as probes for complex plasmas in front of biased surfaces
An interesting aspect in the research of complex (dusty) plasmas is the
experimental study of the interaction of micro-particles with the surrounding
plasma for diagnostic purposes. Local electric fields can be determined from
the behaviour of particles in the plasma, e.g. particles may serve as
electrostatic probes. Since in many cases of applications in plasma technology
it is of great interest to describe the electric field conditions in front of
floating or biased surfaces, the confinement and behaviour of test particles is
studied in front of floating walls inserted into a plasma as well as in front
of additionally biased surfaces. For the latter case, the behaviour of
particles in front of an adaptive electrode, which allows for an efficient
confinement and manipulation of the grains, has been experimentally studied in
dependence on the discharge parameters and on different bias conditions of the
electrode. The effect of the partially biased surface (dc, rf) on the charged
micro-particles has been investigated by particle falling experiments. In
addition to the experiments we also investigate the particle behaviour
numerically by molecular dynamics, in combination with a fluid and
particle-in-cell description of the plasma.Comment: 39 pages, 16 figures, submitted to New J. Phy
Investigation of the Formation and Energy Density of High-Current Pulsed Electron Beams
Study of the electron kinetics in cylindrical hollow cathodes by a multi-term approach
The non-local kinetics of the electrons in a
cylindrical, axially symmetric hollow cathode discharge
is theoretically investigated.
A new multi-term method for solving the inhomogeneous Boltzmann equation
in cylindrical coordinates has been developed
to adequately describe the pronounced anisotropy
of the electron velocity distribution function
expected in the cathode fall region.
This method is based on a tensorial representation of the
expansion of the electron velocity distribution function
in spherical harmonics.
The resultant hierarchy of component equations
has been specified to cylindrical geometry
with rotational symmetry and axial uniformity.
A subset of component equations could be separated
which determines the relevant distribution parts
needed to analyze
the radial behaviour of important electron properties
in the hollow cathode.
Using measured profiles of the electric field,
this subset has numerically been solved
for a helium plasma
at a discharge current of some mA and a pressure of few torr.
Based on this approach in addition to the radial variation
of the energy distribution,
that of important transport properties and collision rates
is studied and the non-local particle and power balance
of the electrons are analysed.
Some theoretical results are compared with available experimental ones