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Dec 2010

Volume 17, Issue 12, Articles (12xxxx)

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Phys. Plasmas 17, 120501 (2010); http://dx.doi.org/10.1063/1.3514586 (36 pages)

A. Bret, L. Gremillet, and M. E. Dieckmann
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back to top Low-Temperature Plasmas, Plasma Applications, Plasma Sources, Sheaths

Electrical and kinetical aspects of homogeneous dielectric-barrier discharge in xenon for excimer lamps

A. Belasri and Z. Harrache

Phys. Plasmas 17, 123501 (2010); http://dx.doi.org/10.1063/1.3520368 (10 pages)

Online Publication Date: 1 December 2010

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A pulsed dielectric-barrier discharge in xenon has been simulated for operating conditions typical to excimer lamps, in which the discharge is considered spatially homogeneous. The computer model developed is based on the xenon plasma chemistry, the circuit, and the Boltzmann equations. First, the validity of the physical model was checked and compared to experimental and theoretical works, and then the model is applied in the case of a sinusoidal voltage at period frequencies in the range of 50 kHz–2 MHz. The results obtained with the present description are in good agreement with experimental measurements and one-dimensional fluid prediction in terms of electrical characteristics and vacuum ultraviolet (vuv) emission. The effect of operation voltage, power source frequency, dielectric capacitance, as well as gas pressure on the discharge efficiency and the 172, 150, and 147 nm photon generation, under the typical experimental operating conditions and for the case of a sinusoidal applied voltage, have been investigated and discussed. Calculations suggest that the overall conversion efficiency from electrical energy to vuv emission in the lamp is greater than 38%, and it will be very affected at high power source frequency and high gas pressure with a significant dependence on the dielectric capacitance.
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51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
52.65.-y Plasma simulation
52.80.-s Electric discharges
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Highly effective fungal inactivation in He+O2 atmospheric-pressure nonequilibrium plasmas

Z. Xiong, X. P. Lu, A. Feng, Y. Pan, and K. Ostrikov

Phys. Plasmas 17, 123502 (2010); http://dx.doi.org/10.1063/1.3526678 (6 pages) | Cited 3 times

Online Publication Date: 7 December 2010

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Highly effective (more than 99.9%) inactivation of a pathogenic fungus Candida albicans commonly found in oral, respiratory, digestive, and reproduction systems of a human body using atmospheric-pressure plasma jets sustained in He+O2 gas mixtures is reported. The inactivation is demonstrated in two fungal culture configurations with open (Petri dish without a cover) and restricted access to the atmosphere (Petri dish with a cover) under specific experimental conditions. It is shown that the fungal inactivation is remarkably more effective in the second configuration. This observation is supported by the scanning and transmission electron microscopy of the fungi before and after the plasma treatment. The inactivation mechanism explains the experimental observations under different experimental conditions and is consistent with the reports by other authors. The results are promising for the development of advanced health care applications.
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52.77.-j Plasma applications
52.75.-d Plasma devices
52.80.-s Electric discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
87.80.-y Biophysical techniques (research methods)
87.16.-b Subcellular structure and processes

Simulations of multipactor in circular waveguides

V. E. Semenov, N. A. Zharova, D. Anderson, M. Lisak, and J. Puech

Phys. Plasmas 17, 123503 (2010); http://dx.doi.org/10.1063/1.3526674 (7 pages) | Cited 1 time

Online Publication Date: 9 December 2010

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Detailed numerical simulations have been done to investigate the properties of multipactor breakdown in circular waveguides operating in the propagating fundamental TE11 mode. Main attention has been given to a comparison between the two fundamental cases corresponding to linear and circular polarizations, respectively, of the propagating electromagnetic wave. It is found that circular polarization is considerably more susceptible to multipactor than linear polarization. The reason for this difference is clarified by a comprehensive study of the electron motion in the waveguide.
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52.80.Pi High-frequency and RF discharges
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.Fi Transport properties
52.65.Rr Particle-in-cell method
52.65.Pp Monte Carlo methods

Negative refractive index designed in a periodic composite of lossy microplasmas and microresonators

Osamu Sakai, Takuya Shimomura, and Kunihide Tachibana

Phys. Plasmas 17, 123504 (2010); http://dx.doi.org/10.1063/1.3524561 (9 pages) | Cited 1 time

Online Publication Date: 13 December 2010

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A novel metamaterial with negative refractive index was designed using a spatially periodic composite of microplasmas and microresonators. Microresonators, which are double-helix metal wires in this report, work as an origin of macroscopic negative permeability material, as well as discharge electrodes. If a resonance frequency of the resonators is well below electron plasma frequency of the microplasmas where their permittivity is negative in the real part with a certain imaginary part, the macroscopic refractive index becomes negative just above the resonance frequency where the macroscopic permeability is negative, even if microplasmas are fairly lossy; due to such a loss or conductive component in permittivity, electromagnetic waves are not evanescent but propagating. This result indicates that plasmas can play important roles in parameter control of a metamaterial with a complex refractive index.
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42.70.Qs Photonic bandgap materials
07.10.Cm Micromechanical devices and systems
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.80.-s Electric discharges

Pattern formation and propagation during microwave breakdown

Bhaskar Chaudhury, Jean-Pierre Boeuf, and Guo Qiang Zhu

Phys. Plasmas 17, 123505 (2010); http://dx.doi.org/10.1063/1.3517177 (11 pages) | Cited 5 times

Online Publication Date: 14 December 2010

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During microwave breakdown at atmospheric pressure, a sharp plasma front forms and propagates toward the microwave source at high velocities. Experiments show that the plasma front may exhibit a complex dynamical structure or pattern composed of plasma filaments aligned with the wave electric field and apparently moving toward the source. In this paper, we present a model of the pattern formation and propagation under conditions close to recent experiments. Maxwell’s equations are solved together with plasma fluid equations in two dimensions to describe the space and time evolution of the wave field and plasma density. The simulation results are in excellent agreement with the experimental observations. The model provides a physical interpretation of the pattern formation and dynamics in terms of ionization-diffusion and absorption-reflection mechanisms. The simulations allow a good qualitative and quantitative understanding of different features such as plasma front velocity, spacing between filaments, maximum plasma density in the filaments, and influence of the discharge parameters on the development of well-defined filamentary plasma arrays or more diffuse plasma fronts.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.30.-q Plasma dynamics and flow
52.50.-b Plasma production and heating
52.80.-s Electric discharges

A numerical method for determining highly precise electron energy distribution functions from Langmuir probe characteristics

Jin-Young Bang and Chin-Wook Chung

Phys. Plasmas 17, 123506 (2010); http://dx.doi.org/10.1063/1.3511445 (5 pages) | Cited 3 times

Online Publication Date: 17 December 2010

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Electron energy distribution functions (EEDFs) were determined from probe characteristics using a numerical ac superimposed method with a distortion correction of high derivative terms by varying amplitude of a sinusoidal perturbation voltage superimposed onto the dc sweep voltage, depending on the related electron energy. Low amplitude perturbation applied around the plasma potential represented the low energy peak of the EEDF exactly, and high amplitude perturbation applied around the floating potential was effective to suppress noise or distortion of the probe characteristic, which is fatal to the tail electron distribution. When a small random noise was imposed over the stabilized prove characteristic, the numerical differentiation method was not suitable to determine the EEDF, while the numerical ac superimposed method was able to obtain a highly precise EEDF.
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52.25.Fi Transport properties
52.70.Ds Electric and magnetic measurements
02.60.Jh Numerical differentiation and integration

Electrostatic beams from tailored plasmas in a Penning–Malmberg trap

T. R. Weber, J. R. Danielson, and C. M. Surko

Phys. Plasmas 17, 123507 (2010); http://dx.doi.org/10.1063/1.3529370 (10 pages) | Cited 1 time

Online Publication Date: 21 December 2010

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In recent work, a technique was developed to extract high quality beams from single-component plasmas confined in a Penning–Malmberg trap in a 4.8 T magnetic field. In this paper, a procedure is developed to extract these beams from the confining magnetic field and then focus them to create especially tailored electrostatic beams. Electron beams are extracted from the field in two stages: they are first transported to a region of reduced field (1 mT), and then taken to zero field with a nonadiabatic, fast extraction. Once in the field-free region, the beams are focused using an Einzel lens. Experimental results and numerical simulations are presented to illustrate the extraction and focusing process. Theoretical expressions are developed to describe the modifications to the relevant beam energy and spatial distributions. Where possible, analytic expressions are presented for the case relevant here of beams with Gaussian radial profiles. Beam emittance considerations are discussed as well as prospects for further development of these techniques. Application of these techniques to provide high-quality positron beams is also discussed.
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52.27.Jt Nonneutral plasmas
41.75.Fr Electron and positron beams
41.85.-p Beam optics
41.85.Ne Electrostatic lenses, septa

Current distribution measurements inside an electromagnetic plasma gun operated in a gas-puff mode

Flavio R. Poehlmann, Mark A. Cappelli, and Gregory B. Rieker

Phys. Plasmas 17, 123508 (2010); http://dx.doi.org/10.1063/1.3526603 (11 pages)

Online Publication Date: 28 December 2010

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Measurements are presented of the time-dependent current distribution inside a coaxial electromagnetic plasma gun. The measurements are carried out using an array of six axially distributed dual-Rogowski coils in a balanced circuit configuration. The radial current distributions indicate that operation in the gas-puff mode, i.e., the mode in which the electrode voltage is applied before injection of the gas, results in a stationary ionization front consistent with the presence of a plasma deflagration. The effects of varying the bank capacitance, transmission line inductance, and applied electrode voltage were studied over the range from 14 to 112 μF, 50 to 200 nH, and 1 to 3 kV, respectively.
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52.25.Fi Transport properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.75.-d Plasma devices
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.80.-s Electric discharges
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