236 research outputs found
Xenon Excimer Emission From Pulsed Microhollow Cathode Discharges
By applying electrical pulses of 20 ns duration to xenon microplasmas, generated by direct current microhollow cathode discharges, we were able to increase the xenon excimer emission by more than an order of magnitude over direct current discharge excimer emission. For pulsed voltages in excess of 500 V, the optical power at 172 nm was found to increase exponentially with voltage. Largest values obtained were 2.75 W of vacuum-ultraviolet optical power emitted from a single microhollow cathode discharge in 400 Torr xenon with a 750 V pulse applied to a discharge. Highest radiative emittance was 15.2 W/cm2. The efficiency for excimer emission was found to increase linearly with pulsed voltages above 500 V reaching values of 20% at 750 V
Resonant Energy Transfer From Argon Dimers to Atomic Oxygen in Microhollow Cathode Discharges
The emission of atomic oxygen lines at 130.2 and 130.5 nm from a microhollow cathode discharge in argon with oxygen added indicates resonant energy transfer from argon dimers to oxygen atoms. The internal efficiency of the vacuum-ultraviolet (VUV) radiation was measured as 0.7% for a discharge in 1100 Torr argon with 0.1% oxygen added. The direct current VUV point source operates at voltages below 300 V and at current levels of milliamperes
PIV-based dynamic model of EHD volume force produced by a surface dielectric barrier discharge
In this paper, an experimental measurement of the f low produced by a surface DBD plasma actuator has been conducted. One original aspect of these measurements by particle image velocimetry is the high acquisition rate for a PIV system (20 kHz). By using these highly- resolved flow measurements, the fluid flow velocity is used to estimate the spatial and temporal evolution of the EHD volume force. A reduced order model of this force has been constructed by proper orthogonal decomposition. Based on the analy sis of the time-resolved expansion coefficients and their associated spatial modes, it is shown that the volume force can be reconstructed by using a limited number of POD mode s (6 modes). This spatial and temporal filtering of the force fields remains faithful to t he original data and it will help in view of an implementation of such a source term in a numerical solver. The resulting dynamic model shows an alternation of positive and negative volume forc es. The strong positive EHD force developing in the glow regime of the DBD plasma discharge is v isualized in a time-resolved manner. This positive force is immediately followed by a strong negative volume force probably caused by the local flow deceleration
Inception and propagation of positive streamers in high-purity nitrogen: effects of the voltage rise-rate
Controlling streamer morphology is important for numerous applications. Up to
now, the effect of the voltage rise rate was only studied across a wide range.
Here we show that even slight variations in the voltage rise can have
significant effects. We have studied positive streamer discharges in a 16 cm
point-plane gap in high-purity nitrogen 6.0, created by 25 kV pulses with a
duration of 130 ns. The voltage rise varies by a rise rate from 1.9 kV/ns to
2.7 kV/ns and by the first peak voltage of 22 to 28 kV. A structural link is
found between smaller discharges with a larger inception cloud caused by a
faster rising voltage. This relation is explained by the greater stability of
the inception cloud due to a faster voltage rise, causing a delay in the
destabilisation. Time-resolved measurements show that the inception cloud
propagates slower than an earlier destabilised, more filamentary discharge.
This explains that the discharge with a faster rising voltage pulse ends up to
be shorter. Furthermore, the effect of remaining background ionisation in a
pulse sequence has been studied, showing that channel thickness and branching
rate are locally affected, depending on the covered volume of the previous
discharge.Comment: 16 pages, 9 figure
Energy deposition characteristics of nanosecond dielectric barrier discharge plasma actuators: Influence of dielectric material
Propagation and Structure of Planar Streamer Fronts
Streamers often constitute the first stage of dielectric breakdown in strong
electric fields: a nonlinear ionization wave transforms a non-ionized medium
into a weakly ionized nonequilibrium plasma. New understanding of this old
phenomenon can be gained through modern concepts of (interfacial) pattern
formation. As a first step towards an effective interface description, we
determine the front width, solve the selection problem for planar fronts and
calculate their properties. Our results are in good agreement with many
features of recent three-dimensional numerical simulations.
In the present long paper, you find the physics of the model and the
interfacial approach further explained. As a first ingredient of this approach,
we here analyze planar fronts, their profile and velocity. We encounter a
selection problem, recall some knowledge about such problems and apply it to
planar streamer fronts. We make analytical predictions on the selected front
profile and velocity and confirm them numerically.
(abbreviated abstract)Comment: 23 pages, revtex, 14 ps file
Surface electrons at plasma walls
In this chapter we introduce a microscopic modelling of the surplus electrons
on the plasma wall which complements the classical description of the plasma
sheath. First we introduce a model for the electron surface layer to study the
quasistationary electron distribution and the potential at an unbiased plasma
wall. Then we calculate sticking coefficients and desorption times for electron
trapping in the image states. Finally we study how surplus electrons affect
light scattering and how charge signatures offer the possibility of a novel
charge measurement for dust grains.Comment: To appear in Complex Plasmas: Scientific Challenges and Technological
Opportunities, Editors: M. Bonitz, K. Becker, J. Lopez and H. Thomse
Numerical simulation of an oxygen-fed wire-to-cylinder negative corona discharge in the glow regime
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