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Jul 2012

Volume 19, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Phys. Plasmas 19, 070701 (2012); http://dx.doi.org/10.1063/1.4736716 (4 pages)

Tomáš Hoder, Hans Höft, Manfred Kettlitz, Klaus-Dieter Weltmann, and Ronny Brandenburg
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back to top Lasers, Particle Beams, Accelerators, Radiation Generation

Quasi-monoenergetic spectra from reactions in a beam-target plasma

B. Appelbe and J. Chittenden

Phys. Plasmas 19, 073115 (2012); http://dx.doi.org/10.1063/1.4739767 (7 pages) | Cited 1 time

Online Publication Date: 27 July 2012

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We investigate the kinematics of two-body (m1+m2→m3+m4) fusion reactions occurring when a beam interacts with a plasma target. An exact expression for the energy spectrum of the product particles is derived. The derivation shows that there is an anisotropic lower limit on the energy of one of the product species. There is a range of beam energies for which this limit acts to suppress thermal broadening of the energy spectra of the particles emitted in the beam direction. The beam energy at which maximum suppression occurs is identified. At this beam energy, the width of the spectrum can be up to a couple of orders of magnitude narrower than the spectrum produced by a thermal plasma. The results indicate that the highly monoenergetic beams of fusion product particles may be produced from hot plasma targets.
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52.40.Mj Particle beam interactions in plasmas
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Quasi-monoenergetic protons accelerated by laser radiation pressure and shocks in thin gaseous targets

Min-Qing He, Xi Shao, Chuan-Sheng Liu, Tung-Chang Liu, Jao-Jang Su, Galina Dudnikova, Roald Z. Sagdeev, and Zheng-Ming Sheng

Phys. Plasmas 19, 073116 (2012); http://dx.doi.org/10.1063/1.4740053 (5 pages) | Cited 1 time

Online Publication Date: 31 July 2012

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Recent experiments and simulations have demonstrated effective CO2 laser acceleration of quasi-monoenergetic protons from thick gaseous hydrogen target (of thickness tens of laser wavelengths) via hole boring and shock accelerations. We present here an alternative novel acceleration scheme by combining laser radiation pressure acceleration with shock acceleration of protons in a thin gaseous target of thickness several laser wavelengths. The laser pushes the thin gaseous plasma forward while compressing it with protons trapped in it. We demonstrated the combined acceleration with two-dimensional particle-in-cell simulation and obtained quasi-monoenergetic protons ∼44 MeV in a gas target of thickness twice of the laser wavelength irradiated by circularly polarized CO2 laser with normalized laser amplitude a0 = 10.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.65.Rr Particle-in-cell method
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
back to top Radiation: Emission, Absorption, Transport

Effect of electron density profile on power absorption of high frequency electromagnetic waves in plasma

Yan-Bin Xi (奚衍斌) and Yue Liu (刘悦)

Phys. Plasmas 19, 073301 (2012); http://dx.doi.org/10.1063/1.4736981 (6 pages)

Online Publication Date: 12 July 2012

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Considering different typical electron density profiles, a multi slab approximation model is built up to study the power absorption of broadband (0.75–30 GHz) electromagnetic waves in a partially ionized nonuniform magnetized plasma layer. Based on the model, the power absorption spectra for six cases are numerically calculated and analyzed. It is shown that the absorption strongly depends on the electron density fluctuant profile, the background electron number density, and the collision frequency. A potential optimum profile is also analyzed and studied with some particular parameters.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.40.Hf Plasma-material interactions; boundary layer effects
52.20.Fs Electron collisions
52.25.Gj Fluctuation and chaos phenomena
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Plume splitting and rebounding in a high-intensity CO2 laser induced air plasma

Anmin Chen, Yuanfei Jiang, Hang Liu, Mingxing Jin, and Dajun Ding

Phys. Plasmas 19, 073302 (2012); http://dx.doi.org/10.1063/1.4737165 (5 pages) | Cited 2 times

Online Publication Date: 17 July 2012

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The dynamics of plasma plume formed by high-intensity CO2 laser induced breakdown of air at atmospheric pressure is investigated. The laser wavelength is 10.6 μm. Measurements were made using 3 ns gated fast photography as well as space and time resolved optical emission spectroscopy. The behavior of the plasma plume was studied with a laser energy of 3 J and 10 J. The results show that the evolution of the plasma plume is very complicated. The splitting and rebounding of the plasma plume is observed to occur early in the plumes history.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Polarizabilities of Li and Na in Debye plasmas

H. W. Li and Sabyasachi Kar

Phys. Plasmas 19, 073303 (2012); http://dx.doi.org/10.1063/1.4739229 (6 pages) | Cited 6 times

Online Publication Date: 20 July 2012

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We have carried out calculations to investigate the effect of Debye plasmas on the dipole, quadrupole, octupole polarizabilities of lithium and sodium atoms using the symplectic algorithm in the framework of the pseudo-state summation technique. The polarizabilities of alkali-metal atoms for various Debye lengths are reported for the first time in the literature. The behavior of the transition energies and oscillator strengths for Li and Na in plasma environments is also presented. In free atomic cases, our calculated results are in good agreement with the reported theoretical and experimental results.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
32.30.-r Atomic spectra
32.70.Cs Oscillator strengths, lifetimes, transition moments

Higher order terms of radiative damping in extreme intense laser-matter interaction

Rishi R. Pandit and Yasuhiko Sentoku

Phys. Plasmas 19, 073304 (2012); http://dx.doi.org/10.1063/1.4739442 (9 pages)

Online Publication Date: 27 July 2012

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The higher order terms of the Lorentz-Abraham-Dirac equation have been derived, and their effects are studied via a relativistic collisional particle-in-cell simulation. The dominant group of terms up to the fourth order of the Lorentz-Abraham-Dirac equation is identified for ultra-intense laser-matter interactions. The second order terms are found to be the damping terms of the Lorentz force while the first order terms represent friction in the equation of motion. Because the second order terms restrict electron acceleration during the laser interaction, electrons/ions are prevented from over-accelerating. Radiative damping becomes highly significant when I ≥  1022 W/cm2 while Bremsstrahlung will be saturated, thus radiative damping will be a dominant source of hard x-rays in regimes at extreme intensities.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.59.Px Hard X-ray sources
52.65.Rr Particle-in-cell method
52.20.Fs Electron collisions
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.27.Ny Relativistic plasmas
back to top Low-Temperature Plasmas, Plasma Applications, Plasma Sources, Sheaths

Kr II and Xe II axial velocity distribution functions in a cross-field ion source

A. Lejeune, G. Bourgeois, and S. Mazouffre

Phys. Plasmas 19, 073501 (2012); http://dx.doi.org/10.1063/1.4731688 (8 pages) | Cited 2 times

Online Publication Date: 3 July 2012

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Laser induced fluorescence measurements were carried out in a cross-field ion source to examine the behaviour of the axial ion velocity distribution functions (VDFs) in the expanding plasma. In the present paper, we focus on the axial VDFs of Kr II and Xe II ions. We examine the contourplots in a 1D-phase space (x,vx) representation in front of the exhaust channel and along the centerline of the ion source. The main ion beam, whose momentum corresponds to the ions that are accelerated through the whole potential drop, is observed. A secondary structure reveals the ions coming from the opposite side of the channel. We show that the formation of the neutralized ion flow is governed by the annular geometry. The assumption of a collisionless shock or a double layer due to supersonic beam interaction is not necessary. A non-negligible fraction of slow ions originates in local ionization or charge-exchange collision events between ions of the expanding plasma and atoms of the background residual gas. Slow ions that are produced near the centerline in the vicinity of the exit plane are accelerated toward the source body with a negative velocity leading to a high sputtering of front face. On the contrary, the ions that are produced in the vicinity of the channel exit plane are partially accelerated by the extended electric field.
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52.25.Fi Transport properties
52.50.Dg Plasma sources
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Jm Ionization of plasmas
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Heavy-fermion instability in double-degenerate plasmas

M. Akbari-Moghanjoughi

Phys. Plasmas 19, 073502 (2012); http://dx.doi.org/10.1063/1.4731726 (9 pages)

Online Publication Date: 10 July 2012

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In this work, we study the propagations of normal frequency modes for quantum hydrodynamic waves in the linear limit and introduce a new kind of instability in a double-degenerate plasma. Three different regimes, namely, low, intermediate, and high magnetic field strengths are considered which span the applicability of the work to a wide variety of environments. Distinct behavior is observed for different regimes, for instance, in the laboratory-scale field regime no frequency-mode instability occurs unlike those of intermediate and high magnetic-field strength regimes. It is also found that the instability of this kind is due to the heavy-fermions which appear below a critical effective-mass parameter (μcr = math) and that the responses of the two (lower and upper frequency) modes to fractional effective-mass change in different effective-mass parameter ranges (below and above the critical value) are quite opposite to each other. It is shown that the heavy-fermion instability due to extremely high magnetic field such as that encountered for a neutron-star crust can lead to confinement of stable propagations in both lower and upper frequency modes to the magnetic poles. Current study can have important implications for linear wave dynamics in both laboratory and astrophysical environments possessing high magnetic fields.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.-s Magnetic confinement and equilibrium
52.72.+v Laboratory studies of space- and astrophysical-plasma processes

A finite-difference time-domain simulation of high power microwave generated plasma at atmospheric pressures

Patrick J. Ford, Sterling R. Beeson, Hermann G. Krompholz, and Andreas A. Neuber

Phys. Plasmas 19, 073503 (2012); http://dx.doi.org/10.1063/1.4736863 (8 pages) | Cited 2 times

Online Publication Date: 10 July 2012

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A finite-difference algorithm was developed to calculate several RF breakdown parameters, for example, the formative delay time that is observed between the initial application of a RF field to a dielectric surface and the formation of field-induced plasma interrupting the RF power flow. The analysis is focused on the surface being exposed to a background gas pressure above 50 Torr. The finite-difference algorithm provides numerical solutions to partial differential equations with high resolution in the time domain, making it suitable for simulating the time evolving interaction of microwaves with plasma; in lieu of direct particle tracking, a macroscopic electron density is used to model growth and transport. This approach is presented as an alternative to particle-in-cell methods due to its low complexity and runtime leading to more efficient analysis for a simulation of a microsecond scale pulse. The effect and development of the plasma is modeled in the simulation using scaling laws for ionization rates, momentum transfer collision rates, and diffusion coefficients, as a function of electric field, gas type and pressure. The incorporation of plasma material into the simulation involves using the Z-transform to derive a time-domain algorithm from the complex frequency-dependent permittivity of plasma. Therefore, the effect of the developing plasma on the instantaneous microwave field is calculated. Simulation results are compared with power measurements using an apparatus designed to facilitate surface flashover across a polycarbonate boundary in a controlled N2, air, or argon environment at pressures exceeding 50 Torr.
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52.80.Pi High-frequency and RF discharges
02.70.Bf Finite-difference methods
52.25.Fi Transport properties
52.25.Mq Dielectric properties
52.40.Hf Plasma-material interactions; boundary layer effects
52.65.Rr Particle-in-cell method

Influence of heat and particle fluxes nonlocality on spatial distribution of plasma density in two-chamber inductively coupled plasma sources

A. A. Kudryavtsev and K. Yu. Serditov

Phys. Plasmas 19, 073504 (2012); http://dx.doi.org/10.1063/1.4731734 (6 pages)

Online Publication Date: 11 July 2012

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This study presents 2D simulations of the two-chamber inductively coupled plasma source where power is supplied in the small discharge chamber and extends by electron thermal conductivity mechanism to the big diffusion chamber. Depending on pressure, two main scenarios of plasma density and its spatial distribution behavior were identified. One case is characterized by the localization of plasma in the small driver chamber where power is deposed. Another case describes when the diffusion chamber becomes the main source of plasma with maximum of the electron density. The differences in spatial distribution are caused by local or non-local behavior of electron energy transport in the discharge volume due to different characteristic scale of heat transfer with electronic conductivity.
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52.50.Dg Plasma sources
52.25.Fi Transport properties
52.65.-y Plasma simulation

Simulation studies for operating electron beam ion trap at very low energy for disentangling edge plasma spectra

Xuelong Jin, Zejie Fei, Jun Xiao, Di Lu, Roger Hutton, and Yaming Zou

Phys. Plasmas 19, 073505 (2012); http://dx.doi.org/10.1063/1.4736855 (8 pages) | Cited 1 time

Online Publication Date: 11 July 2012

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Electron beam ion traps (EBITs) are very useful tools for disentanglement studies of atomic processes in plasmas. In order to assist studies on edge plasma spectroscopic diagnostics, a very low energy EBIT, SH-PermEBIT, has been set up at the Shanghai EBIT lab. In this work, simulation studies for factors which hinder an EBIT to operate at very low electron energies were made based on the Tricomp (Field Precision) codes. Longitudinal, transversal, and total kinetic energy distributions were analyzed for all the electron trajectories. Influences from the electron current and electron energy on the energy depression caused by the space charge are discussed. The simulation results show that although the energy depression is most serious along the center of the electron beam, the electrons in the outer part of the beam are more likely to be lost when an EBIT is running at very low energy. Using the simulation results to guide us, we successfully managed to reach the minimum electron beam energy of 60 eV with a beam transmission above 57% for the SH-PermEBIT. Ar and W spectra were measured from the SH-PermEBIT at the apparent electron beam energies (read from the voltage difference between the electron gun cathode and the central drift tube) of 60 eV and 1200 eV, respectively. The spectra are shown in this paper.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.50.Dg Plasma sources
52.65.-y Plasma simulation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Fi Transport properties

Influence of the airflow speed along transmission lines on the DC corona discharge loss, using finite element approach

A. Shemshadi, K. Niayesh, and A. Akbari

Phys. Plasmas 19, 073506 (2012); http://dx.doi.org/10.1063/1.3664310 (10 pages)

Online Publication Date: 12 July 2012

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Corona discharge is of great interest from the physical point of view and due to its numerous practical applications in industry and especially one of the most important sources of loss in the high voltage transmission lines. This paper provides guidelines for the amount of electric loss caused by corona phenomenon occurred around a DC high voltage wire placed between two flat plates and influence of wind speed rate on the amount of corona loss using COMSOL Multiphysics. So electric potential distribution patterns and charge density diffusion around the wire are studied in this article.
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52.25.Fi Transport properties
52.80.Hc Glow; corona
02.70.Dh Finite-element and Galerkin methods

On the space-charge formation in a collisional magnetized electronegative plasma

Kiomars Yasserian and Morteza Aslaninejad

Phys. Plasmas 19, 073507 (2012); http://dx.doi.org/10.1063/1.4736861 (7 pages)

Online Publication Date: 12 July 2012

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The plasma sheath formation in the vicinity of a surrounding wall of magnetized plasma is studied in the presence of the electronegative ions and the positive ion-neutral background collisions. Fluid equations are used to treat the plasma particles species. By using the Sagdeev potential, the influence of the collisions and the magnetic field on the Bohm criterion are investigated. The space-charge profiles are obtained in the presence of a magnetic field in different collision frequencies as well as electronegative ions concentration. It is shown that the collision and the magnetic field raise a space-charge peak, while the presence of the electronegative ions results in damping the peaks. Moreover, it is observed that in the case of high magnetic field, some fluctuations emerge in the space-charge profiles. The influences of the magnetic field and electronegative ion concentration as well as negative ion temperature on the positive ion kinetic energy reaching the plasma surrounding wall and positive ion velocity perpendicular to the sheath axis are investigated. Finally, the net current through the sheath region is obtained for different collisionality and magnetic field values in both electropositive and electronegative plasmas.
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52.25.Xz Magnetized plasmas
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Kh Plasma sheaths
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena

Bare-tether cathodic contact through thermionic emission by low-work-function materials

Xin Chen and J. R. Sanmartín

Phys. Plasmas 19, 073508 (2012); http://dx.doi.org/10.1063/1.4736987 (9 pages)

Online Publication Date: 12 July 2012

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A new material, C12A7:e- electride, which might present a work function as low as 0.6 eV and moderately high temperature stability, was recently proposed as coating for floating bare tethers. Arising from heating under space operation, current is emitted by thermionic emission along a thus coated cathodic segment. A preliminary study on the space-charge-limited (SCL) double layer in front of the cathodic segment is presented using Langmuir’s SCL electron current between cylindrical electrodes and orbital-motion-limited ion-collection sheath. A detailed calculation of current and bias profiles along the entire tether length is carried out with ohmic effects and the transition from SCL to full Richardson-Dushman emission included. Analysis shows that in the simplest drag mode, under typical orbital and tether conditions, thermionic emission leads to a short cathodic section and may eliminate the need for an active cathodic device and its corresponding gas feed requirements and power subsystem, which results in a truly “propellant-less” tether system for such basic applications as de-orbiting low earth orbit satellites.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.40.Kh Plasma sheaths
52.50.Nr Plasma heating by DC fields; ohmic heating, arcs
52.25.Fi Transport properties

Airflow influence on the discharge performance of dielectric barrier discharge plasma actuators

J. Kriegseis, S. Grundmann, and C. Tropea

Phys. Plasmas 19, 073509 (2012); http://dx.doi.org/10.1063/1.4736995 (9 pages) | Cited 2 times

Online Publication Date: 17 July 2012

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In the present work, the effect of the airflow on the performance of dielectric barrier discharge plasma-actuators is investigated experimentally. In order to analyze the actuator’s performance, luminosity measurements have been carried out simultaneously with the recording of the relevant electrical parameters. A performance drop of about 10% is observed for the entire measured parameter range at a flow speed of M = 0.145 (U∞ = 50 m/s). This insight is of particular importance, since the plasma-actuator control authority is already significantly reduced at this modest speed level. The results at higher Mach numbers (0.4<M<0.8) reveal an even more pronounced reduction of about 30%. From the combined analysis, the conclusion is drawn that the decreasing electrical performance PA correlates closely with the decreasing luminosity peak intensity math for increasing airflow velocities. Two non-dimensional scaling numbers are proposed to characterize and quantify the airflow influence. It is demonstrated that these numbers span a universal performance drop diagram for the entire range of investigated operating parameters.
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52.80.-s Electric discharges
52.25.Fi Transport properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.75.-d Plasma devices

Numerical simulation of carbon arc discharge for nanoparticle synthesis

M. Kundrapu and M. Keidar

Phys. Plasmas 19, 073510 (2012); http://dx.doi.org/10.1063/1.4737153 (9 pages) | Cited 1 time

Online Publication Date: 18 July 2012

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Arc discharge with catalyst-filled carbon anode in helium background was used for the synthesis of carbon nanoparticles. In this paper, we present the results of numerical simulation of carbon arc discharges with arc current varying from 10 A to 100 A in a background gas pressure of 68 kPa. Anode sublimation rate and current voltage characteristics are compared with experiments. Distribution of temperature and species density, which is important for the estimation of the growth of nanoparticles, is obtained. The probable location of nanoparticle growth region is identified based on the temperature range for the formation of catalyst clusters.
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52.77.Fv High-pressure, high-current plasmas (plasma spray, arc welding, etc.)
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.63.-b Electronic transport in nanoscale materials and structures
81.16.Hc Catalytic methods
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Influence of magnetic field strength on potential well in the ionization stage of a double stage Hall thruster

Daren Yu (于达仁), Maojiang Song (宋茂江), Hui Liu (刘辉), Xu Zhang (张旭), and Hong Li (李鸿)

Phys. Plasmas 19, 073511 (2012); http://dx.doi.org/10.1063/1.4737174 (7 pages) | Cited 1 time

Online Publication Date: 18 July 2012

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Similar to a single stage Hall thruster, the magnetic field, which controls electron trajectory and electric field distribution, is the most important factor determining the performance of a double stage Hall thruster. Especially, a potential well, which is helpful to reduce the ion loss on the thruster walls, is shaped in the ionization stage due to the existence of an annular magnetic field topology there. In this paper, the influence of magnetic field strength in the ionization stage on the potential well is researched with both experiments and particle-in-cell simulations. It is found that the depth of potential well increases with the magnetic field strength as a result of enhanced magnetic confinement and lowered electron conductivity. Consequently, the plasma density as well as the ion current entering the acceleration stage increases. However, an excessive magnetic field strength leads to an excess of ion loss on the walls of the acceleration stage. Therefore, there is an appropriate magnetic field strength in the ionization stage that results in a proper potential well and consequently an optimal performance of a double stage Hall thruster.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Vd Magnetic reconnection
52.65.Rr Particle-in-cell method
52.80.-s Electric discharges
52.25.Fi Transport properties

Global model of a gridded-ion thruster powered by a radiofrequency inductive coil

P. Chabert, J. Arancibia Monreal, J. Bredin, L. Popelier, and A. Aanesland

Phys. Plasmas 19, 073512 (2012); http://dx.doi.org/10.1063/1.4737114 (7 pages)

Online Publication Date: 19 July 2012

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A global (volume-averaged) model of a gridded-ion thruster is proposed. The neutral propellant (xenon gas) is injected into the thruster chamber at a fixed rate and a plasma is generated by circulating a radiofrequency current in an inductive coil. The ions generated in this plasma are accelerated out of the thruster by a pair of DC biased grids. The neutralization downstream is not treated. Xenon atoms also flow out of the thruster across the grids. The model, based on particle and energy balance equations, solves for four global variables in the thruster chamber: the plasma density, the electron temperature, the neutral gas (atom) density, and the neutral gas temperature. The important quantities to evaluate the thruster efficiency and performances are calculated from these variables and from the voltage across the grids. It is found that the mass utilization efficiency rapidly decreases with the gas flow rate. However, the radiofrequency power transfer efficiency increases significantly with the injected gas flow rate. Therefore, there is a compromise to be found between these two quantities.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.50.Gj Plasma heating by particle beams
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.59.Bi Grid- and ion-diode-accelerated beams

Diagnosis of gas temperature, electron temperature, and electron density in helium atmospheric pressure plasma jet

Zheng-Shi Chang (常正实), Guan-Jun Zhang (张冠军), Xian-Jun Shao (邵先军), and Zeng-Hui Zhang (张增辉)

Phys. Plasmas 19, 073513 (2012); http://dx.doi.org/10.1063/1.4739060 (5 pages)

Online Publication Date: 20 July 2012

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The optical emission spectra of helium atmospheric pressure plasma jet (APPJ) are captured with a three grating spectrometer. The grating primary spectrum covers the whole wavelength range from 200 nm to 900 nm, with the overlapped grating secondary spectrum appearing from 500 nm to 900 nm, which has a higher resolution than that of the grating primary spectrum. So the grating secondary spectrum of OH (A2∑ +(υ′ = 0) → X2П(υ″ = 0)) is employed to calculate the gas temperature (Tg) of helium APPJ. Moreover, the electron temperature (Te) is deduced from the Maxwellian electron energy distribution combining with Tg, and the electron density (ne) is extracted from the plasma absorbed power. The results are helpful for understanding the physical property of APPJs.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.30.-q Plasma dynamics and flow

Physics of the intermediate layer between a plasma and a collisionless sheath and mathematical meaning of the Bohm criterion

N. A. Almeida and M. S. Benilov

Phys. Plasmas 19, 073514 (2012); http://dx.doi.org/10.1063/1.4737080 (10 pages) | Cited 1 time

Online Publication Date: 20 July 2012

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A transformation of the ion momentum equation simplifies a mathematical description of the transition layer between a quasi-neutral plasma and a collisionless sheath and clearly reveals the physics involved. Balance of forces acting on the ion fluid is delicate in the vicinity of the sonic point and weak effects come into play. For this reason, the passage of the ion fluid through the sonic point, which occurs in the transition layer, is governed not only by inertia and electrostatic force but also by space charge and ion-atom collisions and/or ionization. Occurrence of different scenarios of asymptotic matching in the plasma-sheath transition is analyzed by means of simple mathematical examples, asymptotic estimates, and numerical calculations. In the case of a collisionless sheath, the ion speed distribution plotted on the logarithmic scale reveals a plateau in the intermediate region between the sheath and the presheath. The value corresponding to this plateau has the meaning of speed with which ions leave the presheath and enter the sheath; the Bohm speed. The plateau is pronounced reasonably well provided that the ratio of the Debye length to the ion mean free path is of the order of 10−3 or smaller. There is no such plateau if the sheath is collisional and hence no sense in talking of a speed with which ions enter the sheath.
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52.40.Kh Plasma sheaths
52.25.Fi Transport properties

Global rate coefficients for ionization and recombination of carbon, nitrogen, oxygen, and argon

Julien Annaloro, Vincent Morel, Arnaud Bultel, and Pierre Omaly

Phys. Plasmas 19, 073515 (2012); http://dx.doi.org/10.1063/1.4737147 (15 pages) | Cited 3 times

Online Publication Date: 23 July 2012

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The flow field modeling of planetary entry plasmas, laser-induced plasmas, inductively coupled plasmas, arcjets, etc., requires to use Navier-Stokes codes. The kinetic mechanisms implemented in these codes involve global (effective) rate coefficients. These rate coefficients result from the excited states coupling during a quasi-steady state. In order to obtain these global rate coefficients over a wide electron temperature (Te) range for ionization and recombination of carbon, nitrogen, oxygen, and argon, the behavior of their excited states is investigated using a zero-dimensional (time-dependent) code. The population number densities of these electronic states are considered as independent species. Their relaxation is studied within the range 3000  K ≤ Te ≤ 20 000  K and leads to the determination of the ionization (ki) and recombination (kr) global rate coefficients. Comparisons with existing data are performed. Finally, the ratio ki/kr is compared with the Saha equilibrium constant. This ratio increases more rapidly than the equilibrium constant for Te>15 000  K.
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95.30.Qd Magnetohydrodynamics and plasmas
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.72.+v Laboratory studies of space- and astrophysical-plasma processes
52.80.-s Electric discharges

Self-consistent simulation of the initiation of the flashover discharge on vacuum insulator surface

L. B. Cai, J. G. Wang, D. H. Zhang, T. J. Du, X. Q. Zhu, and Y. Wang

Phys. Plasmas 19, 073516 (2012); http://dx.doi.org/10.1063/1.4737195 (5 pages)

Online Publication Date: 23 July 2012

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A 2D particle-in-cell code, including the space charge effects of insulator surface charge, is established to simulate the initiation of insulator surface flashover. The simulation is started with a field electron emission, which provides the seed electrons of the surface flashover discharge. Then the secondary electron emission is caused by the seed electrons on the insulator surface, gets into an avalanche, and saturates rapidly in a region between the cathode and anode. And the saturation region spreads to the anode at a speed of ∼107 m/s, which is coincident with the experiment measurement.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
77.22.Jp Dielectric breakdown and space-charge effects
79.20.Hx Electron impact: secondary emission
79.70.+q Field emission, ionization, evaporation, and desorption
52.65.Rr Particle-in-cell method

Detachment-induced electron production in the early afterglow of pulsed cc-rf oxygen plasmas

C. Küllig, K. Dittmann, and J. Meichsner

Phys. Plasmas 19, 073517 (2012); http://dx.doi.org/10.1063/1.4737196 (8 pages) | Cited 2 times

Online Publication Date: 23 July 2012

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Line integrated electron densities are measured by 160.28 GHz Gaussian beam microwave interferometry in a 10 Hz pulsed (50% duty cycle) cc-rf oxygen discharge, operating at 13.56 MHz. Depending on the processing parameters, the oxygen rf discharge displays two different operation modes regarding its electronegativity. For higher rf power with negative self-bias voltage above −220 V, the oxygen discharge acts as electropositive plasma (n-/ne≪1), whereas at lower rf power and self-bias voltage the plasma becomes strongly electronegative (n-/ne>2). In the latter mode, a significant electron density increase is measured in the early afterglow (<100 μs) within a pressure range from 20 to 100 Pa. By use of a simple rate equation model, the temporal behavior of the electron density could be reproduced for both modes of electronegativity. The electron production in the early afterglow is mainly caused due to the detachment of negative atomic oxygen ions by metastable oxygen molecules.
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52.25.Tx Emission, absorption, and scattering of particles
52.50.Dg Plasma sources
52.70.Gw Radio-frequency and microwave measurements
52.80.Pi High-frequency and RF discharges
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.-b Plasma properties

Modeling the chemical kinetics of atmospheric plasma for cell treatment in a liquid solution

H. Y. Kim, H. W. Lee, S. K. Kang, H. Wk. Lee, G. C. Kim, and J. K. Lee

Phys. Plasmas 19, 073518 (2012); http://dx.doi.org/10.1063/1.4739777 (8 pages) | Cited 2 times

Online Publication Date: 27 July 2012

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Low temperature atmospheric pressure plasmas have been known to be effective for living cell inactivation in a liquid solution but it is not clear yet which species are key factors for the cell treatment. Using a global model, we elucidate the processes through which pH level in the solution is changed from neutral to acidic after plasma exposure and key components with pH and air variation. First, pH level in a liquid solution is changed by He+ and He(21S) radicals. Second, O3 density decreases as pH level in the solution decreases and air concentration decreases. It can be a method of removing O3 that causes chest pain and damages lung tissue when the density is very high. H2O2, HO2, and NO radicals are found to be key factors for cell inactivation in the solution with pH and air variation.
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.45.-h Electrochemistry and electrophoresis
52.25.Dg Plasma kinetic equations
52.65.-y Plasma simulation
82.20.Wt Computational modeling; simulation
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Three-dimensional numerical investigation of electron transport with rotating spoke in a cylindrical anode layer Hall plasma accelerator

D. L. Tang, S. F. Geng, X. M. Qiu, and Paul K. Chu

Phys. Plasmas 19, 073519 (2012); http://dx.doi.org/10.1063/1.4740066 (4 pages) | Cited 4 times

Online Publication Date: 30 July 2012

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The effects of increased magnetic field and pressure on electron transport with a rotating spoke in a cylindrical anode layer Hall plasma accelerator are investigated by three-dimensional particle-in-cell numerical simulation. The azimuthal rotation of electron transport with the spoke has a frequency of 12.5 MHz. It propagates in the direction of the E × B drift at a speed of ∼1.0 × 106 m/s (about 37% of the E × B drift speed). Local charge separation occurs because the azimuthal local electron density concentration is accompanied by an almost uniform azimuthal ion distribution. The non-axisymmetrical electron density concentration and axisymmetrical ion distribution introduce two azimuthal electric fields with opposite directions in the plasma discharge region. The axial electron shear flow is excited under the additional Eθ × B field. The anomalous electron transport with the rotating spoke may be attributed to the axial electron shear flow induced by the two azimuthal electric fields with opposite directions as a result of the azimuthal local electron density concentration.
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52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow
52.59.-f Intense particle beams and radiation sources
52.65.Rr Particle-in-cell method
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