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  • Experimental investigation of sheath effects on I–V traces of strongly electron emitting probes
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-24
    Chi-Shung Yip, Chenyao Jin, Wei Zhang, Guo Sheng Xu and Noah Hershkowitz

    I–V traces of strongly emitting emissive probes are investigated in a multidiople filament discharge. It is found that at sufficiently high neutral pressure and emitting current, the variation of the I–V traces and their associated inflection points no longer follow the previous predictions of space charge limited (SCL) models. A new, steep slope region of the I–V trace appears near the plasma potential when the probe is strongly emitting, causing the inflection point and the floating potential to increase towards the plasma potential as emission current increases, rather than staying constant. This is, to our knowledge, the first experimental evidence that the effects predicted by Campanell et al ’s inverse sheath theory (2017 Physics of Plasmas 24 057101) not only affect the floating potential but also a region in the I–V trace of an emissive probe. It is also found that the double inflection point structure when the probe is bi...

    更新日期:2020-02-24
  • Electron energy probability function in plasma controlled by high-energy run-away electrons
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-24
    D V Lopaev, M A Bogdanova, A V Volynets, A I Zotovich and S M Zyryanov

    The electron energy probability function (EEPF) probe measurements in cold plasma controlled by high-energy (0.5–1 keV) run-away electrons generated in an ‘open-discharge’ configuration are presented in this paper. High plasma stability along with the second harmonic lock-in measurement method provide a sufficiently high accuracy of the EEPF measurements which makes it possible to thoroughly study the features of both cold plasma and the probe method itself. The experiments have been carried out in pure gases: Ar, He, O 2 and H 2 . The run-away electron beam is revealed to produce a lot of cold electrons in each gas and the EEPF is Maxwellian with T e about few tens of meV (which is slightly higher than the gas temperature). It is shown that an EEPF can be correctly measured under these conditions if the modulation amplitude and, accordingly, the energy resolution of the method is less than the electron temperature, T e . At ...

    更新日期:2020-02-24
  • Influence of sputtered species ionisation on the hysteresis behaviour of reactive HiPIMS with oxygen admixture
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-24
    M Fekete, K Bernátová, P Klein, J Hnilica and P Vašina

    In this paper, the hysteresis behaviour of a reactive magnetron sputtering process with oxygen admixture is studied by both experiment and model. The ground state number densities of titanium atoms and ions, and the deposition rates in high power impulse magnetron sputtering discharge were determined for a constant average applied power and pulse duration, while the repetition frequency and reactive gas supply were varied. The hysteresis curve reduced in width and shifted towards the lower oxygen supply with a decrease in the repetition frequency. These experimentally observed trends were well reproduced by a modified Berg model. The presented model utilised measured ionisation fraction of sputtered species and considered the back-attraction of the ionised sputtered species to the target. Significance of the back-attraction process was observed as large fraction of ionised sputtered particles was found to be lost back to the target. This drastically decreased the number of parti...

    更新日期:2020-02-24
  • Erosion and cathodic arc plasma of Nb–Al cathodes: composite versus intermetallic
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-24
    Siegfried Zöhrer, Mehran Golizadeh, Nikola Koutná, David Holec, André Anders and Robert Franz

    Many properties of cathodic arcs from single-element cathodes show a correlation to the cohesive energy of the cathode material. For example, the burning voltage, the erosion rate, or, to a lesser extent, plasma properties like electron temperatures or average ion energy and charge states. For multi-element cathodes, various phases with different cohesive energies can initially be present in the cathode, or form due to arc exposure, complicating the evaluation of such correlations. To test the influence of morphology and phase composition of multi-element cathodes on cathodic arc properties, a Nb–Al cathode model system was used that includes: pure Nb and Al cathodes; intermetallic Nb 3 Al, Nb 2 Al and NbAl 3 cathodes; and three composite Nb–Al cathodes with atomic ratios corresponding to the stoichiometric ratios of the intermetallic phases. Pulsed cathodic arc plasmas from these cathodes were examined using a mass-per-charge and energy-per-charge an...

    更新日期:2020-02-24
  • Development of skeletal kinetics mechanisms for plasma-assisted combustion via principal component analysis
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-19
    Aurélie Bellemans, Nicholas Deak and Fabrizio Bisetti

    The positive effect of plasma discharges on ignition and flame stability motivates the development of detailed kinetic mechanisms for high-fidelity simulations of plasma-assisted combustion. Because of their hierarchical nature, combustion processes require a large number of chemical species and pathways to describe hydrocarbon oxidation. In order to simulate kinetic enhancement by non-thermal electrons, additional species and processes are included, which model the ionization and excitation of neutral molecules. From a practical perspective, integrating large kinetics mechanisms is computationally burdensome due to the temporal stiffness of the nonlinear combustion dynamics and the memory requirements associated with the high number of species. In order to alleviate computational costs, a dimensionality reduction approach is proposed based on principal component analysis. The methodology is demonstrated on a detailed kinetics mechanism for plasma-assisted combustion excited by ...

    更新日期:2020-02-19
  • Maskless and contactless patterned silicon deposition using a localized PECVD process
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-19
    Ronan Leal, Bastien Bruneau, Pavel Bulkin, Tatiana Novikova, François Silva, Nada Habka and Erik V Johnson

    We present a novel technique to perform contactless and mask-free patterned plasma enhanced chemical vapour deposition and etching. When a powered electrode with narrow slits is placed very close to the substrate, plasma is selectively ignited within the slits due to the hollow cathode effect, and so deposition or etching occurs only within an area smaller than the size of the slit. This technique is demonstrated through the deposition of hydrogenated amorphous silicon using a gas mixture of hydrogen, argon and silane. Slits as small as 1 mm generate a plasma, and for this width, the lines deposited are about 750 μ m wide, homogenous over their length (60 mm), and are deposited at a rate of 50 nm min −1 . The phenomenon is studied using 2D Particle In Cell (PIC) modelling with a simplified argon chemistry. The electron localization observed in the PIC modelling provides an explanation of why the deposition is narrower than the slit.

    更新日期:2020-02-19
  • Deep learning for solving the Boltzmann equation of electrons in weakly ionized plasma
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-19
    S Kawaguchi, K Takahashi, H Ohkama and K Satoh

    A novel direct numerical method to calculate the electron velocity distribution function (EVDF) in hydrodynamic equilibrium under a uniform DC electric field is presented. In the present method, an artificial feedforward neural network learns the EVDF governed by both the Boltzmann equation and boundary conditions. The present method dost not require the expansion of the EVDF in the Legendre polynomials and the discretization of both the EVDF and the Boltzmann equation. As a benchmark, the EVDF in Reid’s ramp model gas and Ar gas was calculated by the present method, and then the validity of the present method was demonstrated by comparing electron energy distributions and electron transport coefficients deduced from the EVDF with those calculated by Monte Carlo simulation.

    更新日期:2020-02-19
  • Electron number density measurements in nanosecond repetitively pulsed discharges in water vapor at atmospheric pressure
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-17
    Florent P Sainct, Keiichiro Urabe, Erwan Pannier, Deanna A Lacoste and Christophe O Laux

    This article reports on experiments in a nonequilibrium plasma produced by nanosecond repetitively pulsed (NRP) spark discharges in water vapor at 450 K and atmospheric pressure. The objective is to determine the electron number density in the post-discharge, with spatial and temporal resolution, to gain a better understanding of the discharge development and chemical kinetics. Electron number densities were measured in water vapor from the broadenings and shifts of the H α and H β lines of the hydrogen Balmer series and of the atomic oxygen triplet at 777 nm. For an average reduced electric field of about 150 Td, high electron densities up to 3 × 10 18 cm −3 are measured at the cathode, up to 5 × 10 17 cm −3 at the anode, and up to 4 × 10 16 cm −3 in the interelectrode gap. The high density near the electrodes is attributed to ionization enhancement and secondary electron emission ...

    更新日期:2020-02-18
  • Electron power absorption in low pressure capacitively coupled electronegative oxygen radio frequency plasmas
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-17
    Máté Vass, Sebastian Wilczek, Trevor Lafleur, Ralf Peter Brinkmann, Zoltán Donkó and Julian Schulze

    A thorough understanding of the energy transfer mechanism from the electric field to electrons is of utmost importance for optimisation and control of different plasma sources and processes. This mechanism, called electron power absorption, involves complex electron dynamics in electronegative capacitively coupled plasmas (CCPs) at low pressures, that are still not fully understood. Therefore, we present a spatio-temporally resolved analysis of electron power absorption in low pressure oxygen CCPs based on the momentum balance equation derived from the Boltzmann equation. Data are obtained from 1d3v particle-in-cell/Monte Carlo Collision simulations. In contrast to conventional theoretical models, which predict ‘stochastic/collisionless heating’ to be important at low pressure, we observe the dominance of Ohmic power absorption. In addition, there is an attenuation of ambipolar power absorption at low pressures due to the strong electronegativity, and the presence of electroposi...

    更新日期:2020-02-18
  • Experimental studies of the difference between plasma potentials measured by Langmuir probes and emissive probes in presheaths
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-14
    Peixuan Li, Noah Hershkowitz, Eugene Wackerbarth and Greg Severn

    The plasma potential measured by cylindrical and planar Langmuir probes has been shown to differ from the plasma potential measured by emissive probes in the neighborhood of the presheath near a negatively biased electrode immersed in a weakly collisional low temperature argon plasma. There are two principal results demonstrated in this paper. First, while it is well known that Langmuir probes cannot reliably measure plasma potentials inside of sheaths, results presented here demonstrate that the problem persists in presheaths, the quasineutral plasma bordering sheaths. It is known that emissive probes analyzed in the limit of zero emission accurately measure the plasma potential in the sheath. It is now clear that they are the only known electrostatic probe technique able to measure the plasma potential accurately throughout the presheath. Second, it is shown that the difference between potential measurements made by Langmuir probes and emissive probes in the body of the plasma...

    更新日期:2020-02-14
  • Reconstruction of plasma density profiles by measuring spectra of radiation emitted from oscillating plasma dipoles
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-14
    S Kylychbekov, H S Song, K B Kwon, O Ra, E S Yoon, M Chung, K Yu, S R Yoffe, B Ersfeld, D A Jaroszynski and M S Hur

    We suggest a new method for characterising non-uniform density distributions of plasma by measuring the spectra of radiation emitted from a localised plasma dipole oscillator excited by colliding electromagnetic pulses. The density distribution can be determined by scanning the collision point in space. Two-dimensional particle-in-cell simulations demonstrate the reconstruction of linear and nonlinear density profiles corresponding to laser-produced plasma. The method can be applied to a wide range of plasma, including fusion and low temperature plasmas. It overcomes many of the disadvantages of existing methods that only yield average densities along the path of probe pulses, such as interferometry and spectroscopy.

    更新日期:2020-02-14
  • Comparison of electron heating and energy loss mechanisms in an RF plasma jet operated in argon and helium
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-14
    J Golda, J Held and V Schulz-von der Gathen

    The μ-APPJ is a well-investigated atmospheric pressure RF plasma jet. Up to now, it has mainly been operated using helium as feed gas due to stability restrictions. However, the COST-Jet design including precise electrical probes now offers the stability and reproducibility to create equi-operational plasmas in helium as well as in argon. In this publication, we compare fundamental plasma parameters and physical processes inside the COST reference microplasma jet, a capacitively coupled RF atmospheric pressure plasma jet, under operation in argon and in helium. Differences already observable by the naked eye are reflected in differences in the power-voltage characteristic for both gases. Using an electrical model and a power balance, we calculated the electron density and temperature at 0.6 W to be ##IMG## [http://ej.iop.org/images/0963-0252/29/2/025014/psstab6c81ieqn1.gif] {$9\times {10}^{17}\,{{\rm{m}}}^{-3}$} , 1.2 eV and ##IMG## {$7.8\tim...}

    更新日期:2020-02-14
  • Modeling and plasma characteristics of high-power direct current discharge
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-14
    Lei Chen, Suihan Cui, Wei Tang, Lin Zhou, Tijun Li, Liangliang Liu, Xiaokai An, Zhongcan Wu, Zhengyong Ma, Hai Lin, Xiubo Tian, Ricky KY Fu, Paul K Chu and Zhongzhen Wu

    To obtain both high ionization and high deposition rate, a modified global model for a continuous high-power DC magnetron sputtering (C-HPMS) is established by considering the continuous generation of the hot electrons and the high temperature caused by continuous high-power discharge. The results show that the plasma density is on the order of 10 19 m −3 for power densities of only 183 W cm −2 (Al) and 117 W cm −2 (Cu). The ionization rate exceeds 90% of high-power impulse magnetron sputtering (HiPIMS) (peak power density of 564 W cm −2 ) for a DC power density of 180 W cm −2 , and the total diffusion fluxes of the two targets are 26 (Al) and 30 (Cu) times that of conventional HiPIMS, leading to very high deposition rates. The work provides a theoretical basis for the realization of C-HPMS and gives an enlightenment to the development of deposition equipment for continuous high-power discharges.

    更新日期:2020-02-14
  • Realistic treatment for secondary electron emission in hybrid DC/DF capacitively coupled discharge
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-14
    Jing-Yu Sun, Quan-Zhi Zhang, Yong-Xin Liu and You-Nian Wang

    Particle-in-cell/Monte Carlo collision simulations are performed to investigate the effects of using realistic models for secondary electron emission induced by different plasma species on the discharge characteristics in direct current (DC) superposed radio-frequency (RF) capacitively coupled plasmas (CCPs). A dual-frequency (DF, 60/2 MHz) source is applied on one of the electrodes to sustain the discharge, and an auxiliary DC source is fixed on the opposite electrode to generate energetic secondary electrons (SEs). Realistic models are employed to calculate the secondary electron yields (SEYs) induced by electrons and heavy particles (i.e. ions and fast neutrals) impacting the ‘dirty’ surfaces (e.g. oxidized metal), respectively, in argon discharge at a fixed pressure of 1.5 Pa. The results are compared to those obtained by assuming a constant ion-induced SEYs of γ = 0.1, and a constant elastic reflected electron yield of η el. = 0.2. As the effective ...

    更新日期:2020-02-14
  • Plasma propagation in the microwave window breakdown at the air/dielectric interface
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-14
    Jianwei Zhang, Wei Luo, Ming Jiang, Hongguang Wang, Yongdong Li and Chunliang Liu

    The microwave window breakdown due to the plasma formation greatly limits the power handling capability of high-power microwave systems. However, the experimentally-observed fast plasma propagation cannot be explained using previous theory or simulation results. In this paper, the photoionization is considered to investigate the mechanism of microwave window breakdown at the air/dielectric interface by particle-in-cell simulation. The results show that photoelectrons produced by high-speed photons can profoundly promote discharge above the air/dielectric interface. Then a fast plasma formation and propagation occurs. The speed of plasma propagation can reach 1 × 10 6 m s −1 , which agrees well with experiments. As a result, the transmitting power is attenuated more seriously than the case without the photoionization. Furthermore, the effects of size of microwave window, gas pressure, strength of microwave electric field and distribution of microwave electric f...

    更新日期:2020-02-14
  • Nanosecond pulsed streamer discharges: II. Physics, discharge characterization and plasma processing
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-13
    Douyan Wang and Takao Namihira

    Nanosecond pulsed streamer discharge has unique characteristics that differentiate it from longer discharges. The very fast voltage rise time, peak voltage plateau, short pulse duration, and fast fall time enable a large volume of uniform nonthermal plasma generation at atmospheric pressure. This review explains the physics of nanosecond discharge plasma through experimental and simulated studies for plasma processing techniques. The following are discussed and compared between sub-microsecond and nanosecond discharge plasma: discharge phase transition, discharge propagation, production of chemically active species, temperature change of gas during plasma propagation, electrode geometry, effect of voltage rise rate, voltage polarities, and N 2 /O 2 gas composition ratio in air seeding gas. Nanosecond pulse discharge plasma is characterized by a considerably faster streamer head propagation velocity and reduced gas heating, resulting in a higher energy efficien...

    更新日期:2020-02-13
  • Nanosecond pulsed streamer discharges Part I: Generation, source-plasma interaction and energy-efficiency optimization
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-13
    T Huiskamp

    Streamer discharges generated by nanosecond high-voltage pulses have gained attraction for a variety of reasons, but mainly because they are very efficient for a number of plasma-processing applications. More specifically, researchers have noted that the pulse duration and the rise time of the applied high-voltage pulse have a significant influence on the radical yield of the transient plasmas generated with these pulses; shorter pulses result in higher yields. With the need to study transient plasmas generated by these short pulses comes the need to understand how to generate those pulses and to understand the interaction between the pulse source and the discharge. In this topical review, we will explore the different methods with which to generate nanosecond high-voltage pulses, how the interaction between the pulse source and the discharge may influence the source and the discharge and how to optimize the energy transfer from the pulse source to the discharge.

    更新日期:2020-02-13
  • A novel experimental method of investigating anode-arc-root behaviors in a DC non-transferred arc plasma torch
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-06
    Sun Qiang, Liu Yonghong, Han Yancong, Wu Xinlei, Liu Peng and Jin Hui

    A novel experimental method of investigating anode arc root was presented, and a plasma torch with multiple anodes was designed. With this apparatus, the number of anode arc roots, their position, and movement with changes in plasma current and gas-flow rate were studied. Results showed that multiple anode arc roots can coexist and their number was more related to plasma current than gas-flow rate. The number of anode arc roots increased with increased plasma current. The anode arc root can move forward and backward in the arc plasma jet, and its position was related to current and gas-flow rate. The anode arc root moved forward with increased current, whereas the anode arc root moved forward first and backward with increased gas-flow rate. Based on the finding, a new non-transferred arc model was established. Finally, the anode arc root motion was classified as steady, slight vibration, alternating motion, jumping motion, and multiple arc root modes. These results can serve as ...

    更新日期:2020-02-07
  • Electron density, temperature and the potential structure of spokes in HiPIMS
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-06
    J Held, P A Maaß, V Schulz-von der Gathen and A von Keudell

    In high power impulse magnetron sputtering (HiPIMS) bright plasma spots are observed during the discharge pulses that rotate with velocities in the order of 10 km s −1 in front of the target surface. It has proven very difficult to perform any quantitative measurements on these so-called spokes, which emerge stochastically during the build-up of each plasma pulse. In this paper, we propose a new time shift averaging method to perform measurements integrating over many discharge pulses, but without phase averaging of the spoke location, thus preserving the information of the spoke structure. This method is then applied to perform Langmuir probe measurements, employing magnetized probe theory to determine the plasma parameters inside the magnetic trap region of the discharge. Spokes are found to have a higher plasma density, electron temperature and plasma potential than the surrounding plasma. The electron density slowly rises at the leading edge of the spoke to ...

    更新日期:2020-02-07
  • Implications of thermo-chemical instability on the contracted modes in CO 2 microwave plasmas
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-06
    A J Wolf, T W H Righart, F J J Peeters, W A Bongers and M C M van de Sanden

    Understanding and controlling contraction phenomena of plasmas in reactive flows is essential to optimize the discharge parameters for plasma processing applications such as fuel reforming and gas conversion. In this work, we describe the characteristic discharge modes in a CO 2 microwave plasma and assess the impact of wave coupling and thermal reactivity on the contraction dynamics. The plasma shape and gas temperature are obtained from the emission profile and the Doppler broadening of the 777 nm ##IMG## [http://ej.iop.org/images/0963-0252/29/2/025005/psstab5ecaieqn1.gif] {${\rm{O}}{(}^{5}{\rm{S}}\ \leftarrow \ {}^{5}{\rm{P}})$} oxygen triplet, respectively. Based on these observations, three distinct discharge modes are identified in the pressure range of 10 mbar to atmospheric pressure. We find that discharge contraction is suppressed by an absorption cutoff of the microwave field at the critical electron density, resulting in a homogeneous d...

    更新日期:2020-02-07
  • Study of VUV radiation of hybrid and standard X-pinches on KING electric discharge facility
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-06
    E A Bolkhovitinov, I N Tilikin, T A Shelkovenko, A A Kologrivov, V M Romanova, A A Rupasov and S A Pikuz

    The radiative characteristics of standard and hybrid X-pinches are studied in VUV range on the small-size KING electric discharge facility (200 kA, 190 ns, 45 kV) for the same initial conditions. Studies were performed for different X-pinch materials. A comparative analysis of the VUV spectra was performed and the output energy of soft x-rays and VUV radiation was measured for standard and hybrid X-pinches.

    更新日期:2020-02-07
  • Plasma-sheath transition in multi-fluid models with inertial terms under low pressure conditions: comparison with the classical and kinetic theory
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-04
    Alejandro Alvarez-Laguna, Thierry Magin, Marc Massot, Anne Bourdon and Pascal Chabert

    We present high-order accuracy simulations of the plasma-sheath transition with an ion–electron multi-fluid model that considers the electron inertial terms and the ion pressure gradient. By means of a third-order accuracy time-dependent finite volume scheme, we solve the isothermal multi-fluid equations with realistic ion-to-electron mass ratios. We propose a numerical procedure and boundary conditions that retrieve a steady-state solution of a planar 1D floating sheath. The classical solution to this problem neglects the ion temperature since the model equations present a singularity for a finite ion temperature. The multi-fluid simulations provide a rigorous solution to the plasma-sheath transition without singularities. We compare our solution to the classical theory, finding perfect agreement when the ion-to-electron temperature tends to zero. We discuss the effect of the ion temperature, the electron inertia, and the elastic collisions with neutrals in low-pressure plasmas...

    更新日期:2020-02-04
  • Magnetic field design for miniature pulse Penning ion source
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-04
    N V Mamedov, A V Gubarev, V I Zverev, S P Maslennikov, A A Solodovnikov, A A Uzvolok and D I Yurkov

    Magnetic field configuration for a miniature pulse Penning ion source was designed in this work. The amplitude-time characteristics of discharge and extracted currents were investigated as a function of gas pressure for various magnetic field magnitude and configuration An effect of magnetic field configuration on the Penning’s discharge modes and characteristics of the extraction current impulse were experimentally shown. Stable operation modes of the ion source were found in this work. Also the appropriate ranges of working gas pressure and magnetic field configuration were demonstrated, at which the current pulse of the extracted ions had a quasi-rectangular form. For better understanding real magnetic fields distributions of within the discharge cell magnetic field have been calculated in COMSOL software.

    更新日期:2020-02-04
  • Rydberg states population via three-body and dissociative recombination in low-temperature plasmas of rare gas mixtures
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-04
    V S Lebedev, K S Kislov and A A Narits

    We study various physical mechanisms of electron-ion recombination accompanied by the formation of Rydberg atoms in plasmas containing atomic and molecular ions. Analytical approach to the description of resonant mechanism of ternary electron capture associated with the non-adiabatic energy transfer from free electron to the electronic shell of a quasimolecular ion is developed. Similar technique is used for the evaluation of the integral contribution of all rovibrational states of a bound molecular ion to the Boltzmann-averaged cross section and rate constant of dissociative recombination (DR). Simple expressions for cross sections and rate constants of non-resonant electron capture to Rydberg states in ternary electron-ion-atom collisions are derived in the impulse approximation. We perform a comparative analysis of the efficiencies of resonant and non-resonant three-body recombination of electrons with atomic ions and DR of molecular ions in plasmas of rare gas mixtures, Rg/X...

    更新日期:2020-02-04
  • Relaxation of electronic excitations in ##IMG## [http://ej.iop.org/images/0963-0252/29/2/025004/toc_psstab5f42ieqn1.gif] {${\mathrm{Kr}}_{2}^{+}$} ions in cold krypton plasma
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-02-04
    Cyril Van de Steen, Malika Benhenni, René Kalus, Rajko Ćosić, Florent Xavier Gadéa and Mohammed Yousfi

    Reaction rate constants have been calculated for electronic transitions in ##IMG## [http://ej.iop.org/images/0963-0252/29/2/025004/psstab5f42ieqn3.gif] {${\mathrm{Kr}}_{2}^{+}$} ions and for their decay as induced by collisions with krypton atoms and/or spontaneous radiation processes. The rate constants have then been used in a series of modelings of electronic relaxation in the ions in cold krypton plasmas with the main focus on relaxation times and final states. It has been shown that the collision-induced (non-radiative) relaxation is much faster than the radiative one and completely dominates with typical relaxation times ranging between nanoseconds and microseconds. The relaxation always ends up in the ##IMG## [http://ej.iop.org/images/0963-0252/29/2/025004/psstab5f42ieqn4.gif] {${\mathrm{Kr}}_{2}^{+}$} electronic ground state, high electronic excitations survive for longer times than lower excitations due to spin–orbit coupling ...

    更新日期:2020-02-04
  • Microwave excitation of a low-energy atomic hydrogen
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-31
    Yuji Shimabukuro, Hidenori Takahashi, Shinichi Iwamoto, Koichi Tanaka and Motoi Wada

    Performances of microwave driven compact neutral beam sources of different plasma excitation configurations have been compared in producing directed low energy atomic beams for biomolecular structural analyses. The beam sources include unique impedance matching systems in themselves for reducing the size of the source; a multi-turn spiral antenna successfully excited a hydrogen plasma in a 4 mm inner diameter Al 2 O 3 tube by 2.45 GHz microwave power. A combination of a mirror magnetic field and electron cyclotron resonance has been found effective to realize a source operation at a low operating pressure (∼10 −3 Pa). This magnetic field configuration produced a hydrogen plasma with the optical emission spectrum predominated by atomic lines indicating a high degree of dissociation. The plasma excited in this type of source exhibited a mode transition like behavior which was not confirmed in other source geometries.

    更新日期:2020-01-31
  • Electron impact dissociation of CO 2
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-31
    A S Morillo-Candas, T Silva, B L M Klarenaar, M Grofulović, V Guerra and O Guaitella

    Several CO 2 electron impact dissociation cross sections are available in the literature, different in magnitude and threshold, hindering the understanding of CO 2 dissociation mechanisms under gas discharges. This work reports the experimental validation of the electron impact CO 2 dissociation cross section using two complementary methods: through the comparison of the measured rate coefficients with those derived from cross sections available in literature; and through the comparison of the experimental time evolution of the dissociation fraction with the simulations of a 0D model. A careful experimental approach was designed to avoid any influence from other dissociation mechanisms or chemical reactions. The experimental results match remarkably well the theoretical predictions from Polak and Slovetsky and establish the validity of the dissociation rate coefficients derived from their cross section. This validation supports the use of Polak and ...

    更新日期:2020-01-31
  • Cathode and plasma phenomena in vacuum-arc sources of hydrogen isotope ions: I. Desorption of hydrogen isotopes during the operation of vacuum arc cathode spots
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-31
    I V Uimanov, D L Shmelev, E M Oks, G Yu Yushkov and S A Barengolts

    A model is proposed to describe the desorption of deuterium from a deuterated cathode during the operation of the vacuum arc cathode spot. The model treats a cathode spot as consisting of individual cells and involves a numerical simulation of the temperature fields that arise during the hydrodynamic processes responsible for the formation of microcraters on the cathode surface. Using a deuterated ZrD 0.67 cathode as an example, it is shown that the amount of deuterium desorbed immediately from the crater formed during the operation of the cathode spot cells is several times smaller than the total amount of desorbed deuterium. The main portion of deuterium is desorbed from the hot cathode region adjacent to the crater and from the crater at the stage of its cooling. For a deuterated ZrD 0.67 cathode, the percentage of desorbed deuterium can reach 80% of the total number of evaporated atoms, and it can be even greater if the cathode spot cells operate in the i...

    更新日期:2020-01-31
  • Understanding arc behaviors and achieving the optimal mode in a magnetically-driven gliding arc plasma
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-31
    Jin-Bao Liu, Xiao-Song Li, Jing-Lin Liu and Ai-Min Zhu

    With the aim of understanding the arc behaviors of a gliding arc (GA) in a magnetic field, arc shape, voltage-current characteristics, plasma parameters, rotational frequency and force analysis of a GA in a magnetically-driven 3D GA reactor are investigated. Three modes, straight (S-arc), forward-bent (FB-arc) and reverse-bent (RB-arc) arcs are observed by moving the magnet axially. It is demonstrated that the arc mode depends on the magnetic field, but is independent of the discharge current. The GA is a glow-like discharge with similar plasma parameters in all the modes. The S-arc mode has the fastest rotational frequency and the highest gas-treated fraction, thus is the optimal for gas conversion (ammonia decomposition to hydrogen as a model reaction in this work). A criterion of the S-arc mode, that the azimuthal Lorentz force applied by the magnetic field is proportional to the square of the radial distance, is deduced from the force analysis. In addition, a method to calcu...

    更新日期:2020-01-31
  • 3D PIC-MCC simulation of corona discharge in needle-plate electrode with external circuit
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-31
    Ming Jiang, Yongdong LI, Hongguang Wang, Weidong Ding and Chunliang Liu

    This paper investigates the external circuit effect in corona discharge by means of numerical simulation, while the effect is usually disregarded in previous plasma simulations. A general numerical solution method of serial external circuit, which can compute surface charges on any shape of electrodes adaptively and solve electrode potential and circuit current simultaneously, is developed to support the investigation, due to lack of theoretical solution in irregular electrode systems. Brief description and validation of the scheme are presented in section 2. In general, the accuracy of numerical solution improves with mesh refinement in orthogonal mesh, due to stair step approximation. Simulations are performed in our self-developed 3D PIC-MCC (particle-in-cell, Monte Carlo collision) code with photoionization and external circuit. The simulation model including recently developed photoionization model is described briefly in section 3. Then the simulation results in a needle-p...

    更新日期:2020-01-31
  • Diagnosis of helicon plasma by local OES
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-28
    Ruilin Cui, Ruoyu Han, Kaiyi Yang, Wanying Zhu, Yueqing Wang, Zun Zhang and Jiting Ouyang

    Optical emission spectroscopy (OES) is a common method for characterizing radio frequency (RF) discharge plasmas. Particulary, helicon plasma is featured by its high plasma density among all RF-excited plasmas. In order to obtain the spatial-resolved information of a helicon plasma, local optical emission spectroscopy (LOES) with a 3 mm spatial resolution was proposed and carried out to evaluate the local electron density and temperature. The plasma emission intensity via LOES was measured and compared with the electron density obtained by a RF-compensated Langmuir probe (LP) in Ar, N 2 and Air helicon plasmas, respectively. The results revealed that there existed a functional relationship between some specific lines (LOES) and electron density (LP). Further, helicon plasma characteristics under capacitive (E) , inductive (H), and helicon (W) modes were systemetically investigated based on LOES. Besides, two-dimensional (2D) contour maps for plasma distributions were m...

    更新日期:2020-01-30
  • Improvements for drift-diffusion plasma fluid models with explicit time integration
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-28
    Jannis Teunissen

    Drift-diffusion plasma fluid models are commonly used to simulate electric discharges. Such models can computationally be very efficient if they are combined with explicit time integration. This paper deals with two issues that often arise with such models. First, a high plasma conductivity can severely limit the time step. A fully explicit method to overcome this limitation is presented. This method is compared to the existing semi-implicit method, and it is shown to have several advantages. A second issue is specific to models with the local field approximation. Near strong density and electric field gradients, electrons can diffuse parallel to the field, and unphysically generate ionization. Existing and new approaches to correct this behavior are compared. Details on the implementation of the models and the various approaches are provided.

    更新日期:2020-01-30
  • The importance of cascade emission and metastable excitation in modeling strong atomic oxygen lines in laboratory plasmas
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-28
    James E Caplinger and Glen P Perram

    A collisional-radiative model for optically accessible atomic oxygen lines in laboratory plasmas has been developed to identify dominant mechanisms and assess the validity and utility for plasma diagnostics. A rate sensitivity analysis of the common 777 nm/844 nm line ratio was carried out and used to determine the importance of often ignored mechanisms including cascade emission and metastable excitation. Commonly used basic models for emission of these lines is compared to the model developed here and the mechanisms responsible for disagreement are identified. At low pressures metastable excitation from the ##IMG## [http://ej.iop.org/images/0963-0252/29/1/015011/psstab5e5fieqn1.gif] {$3{\rm{s}}{}^{5}{\rm{S}}^\circ $} state becomes important and at high pressures collisional relaxation of ##IMG## [http://ej.iop.org/images/0963-0252/29/1/015011/psstab5e5fieqn2.gif] {$3{\rm{p}}{}^{3}{\rm{P}}$} to ##IMG## {$3{\rm{p}}{}^{5...}

    更新日期:2020-01-30
  • Volume and surface memory effects on evolution of streamer dynamics along gas/solid interface in high-pressure nitrogen under long-term repetitive nanosecond pulses
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-28
    Z Zhao, D D Huang, Y N Wang, C J Li and J T Li

    Evolution of the surface streamer and the discharge mode transition from the corona discharge to the surface flashover were investigated by pulse sequence resolved electrical and optical measurements under long-term repetitive nanosecond pulses (RNP). The test sample was a cylindrical epoxy resin insulator attached with a needle electrode in 0.1–0.4 MPa nitrogen. Under positive RNP, the inception phase of subsequent streamer discharges decreases with increasing the pulse repetition frequency (PRF), and a periodical streamer stagnation phenomenon appears at high gas pressure. Under negative RNP, the surface streamer does not illustrate symbolic decreasing tendencies in light intensity and corona inception phase in gas gap. The dependence of the evolution of surface streamer velocity on PRF is correlated with the repulsive force from surface charges and the accessibility of seed electrons. Statistical characteristics of back discharges under negative RNP are qualitatively explaine...

    更新日期:2020-01-30
  • Weibull analysis of atmospheric pressure plasma generation and evidence for field emission in microwave split-ring resonators
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-28
    Z Cohick, B Hall, D Wolfe and M Lanagan

    The generation of atmospheric pressure microplasmas using microwave resonators is promising for many applications due to the possibility of high electron densities and low electrode degradation. In particular, such plasmas may help enable reconfigurable metamaterials operating from GHz to THz. Since plasma metamaterials may require the generation of tens to hundreds of plasmas, it is important to find ways to reduce the power required for plasma breakdown. Here, we study gold and silver microwave split-ring resonators (SRRs) with a variety of materials near the interelectrode gap (Cu, CuO nanowires, aluminum oxide). We focus on those fabricated using a traditional thick film technique, screen-printing, and using fs- and ns-laser ablation. The use of laser ablation allows us to explore small interelectrode gap sizes (7–100 μ m) and the use of different lasers and laser parameters enables us to produce a variety of microstructures. We utilize Weibull statistics to examine br...

    更新日期:2020-01-30
  • Ozone and oxygen atoms production in a dielectric barrier discharge in pure oxygen and O 2 /CH 4 mixtures. Modeling and experiment
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-28
    P A Mikheyev, A V Demyanov, I V Kochetov, A A Sludnova, A P Torbin, A M Mebel and V N Azyazov

    This paper describes the results of modeling of a dielectric barrier discharge (DBD). Filamentary structure of DBD is taken into account in the model by introducing the ratio of the cross section area of a microdischarge to the electrode area as a parameter of the model. Discharge and afterglow stages in the gas flow were studied using a zero-dimensional model for a DBD microdischarge channel. The results of modeling are compared with literature data for [O] number densities in a single pulse nanosecond discharge, and with our own measurements of ozone formation in the DBD. Measurements of ozone number density in oxygen and in mixtures of oxygen with methane served as means of validating the DBD model. The best agreement of the calculated and experimental dependences of [O 3 ] number densities on the discharge energy load was observed, when processes involving vibrationally excited ozone were accounted for together with the discharge microstructure.

    更新日期:2020-01-30
  • Ultrasound generated by alternating current dielectric barrier discharge plasma in quiescent air
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-28
    Xin Zhang, Y D Cui, Chien-Ming Jonathan Tay and B C Khoo

    Dielectric barrier discharge (DBD) driven by an alternating current (AC) high-voltage power supply, also called silent discharge, has been known for more than a century since Siemens first proposed the term DBD in 1857, and penetrates into our daily lives. In our traditional view, AC-DBD is considered as an ozone generator for disinfection, an electronic emitter for depollution of gas streams, a jet actuator for flow control, and so on. However, the acoustic effect of AC-DBD is always neglected. Here, we demonstrate that an asymmetrical DBD plasma actuator which was powered by sinusoidal AC waveforms with an AC voltage of 16 kV p–p at a high voltage frequency of a few kHz can generate ultrasound in quiescent air by using a pressure-field microphone and a high accuracy phase-lock image Schlieren technique. The frequency of this induced ultrasound is approximately 100 kHz which is much higher than the sin high voltage frequency of a few kHz. It is the first time that ult...

    更新日期:2020-01-30
  • Dissociative recombination and its impact on the line profile of the hydrogen Balmer series
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-28
    R Friedl, D Rauner, A Heiler and U Fantz

    In low pressure low temperature plasmas ( p ∼ Pa, T e ∼ eV) the upper levels of the Balmer series of the hydrogen atom are populated by several excitation channels. While electron impact excitation is dominant for so-called ionizing plasmas ( T e → 10 eV), dissociative recombination (DR) via the molecular ion ##IMG## [http://ej.iop.org/images/0963-0252/29/1/015014/psstab5ae5ieqn1.gif] {${{\rm{H}}}_{2}^{+}$} becomes dominant in so-called recombining plasmas ( T e → ≲ 1 eV). In the intermediate range, several other channels may be relevant as well. The expansion region of an ECR discharge, which represents such a plasma, is analyzed regarding the composition of the excitation processes as well as the line profiles of the Balmer series (for H α to H δ ). Significantly broadened line profiles compared to Doppler broadening of thermal hydrogen atoms are revealed. The r...

    更新日期:2020-01-30
  • Experimental and PIC MCC study of electron cooling—re-heating and plasma density decay in low pressure rf ccp argon afterglow
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-28
    O V Proshina, T V Rakhimova, A S Kovalev, A N Vasilieva, A I Zotovich, S M Zyryanov and A T Rakhimov

    In this work, experimental and theoretical study of pulsed discharge in argon has been carried out. The experimental data on the dynamics of electron density, electron temperature, and plasma potential have been obtained by probe measurements (using hairpin and Langmuir probes) in the afterglow between two RF pulses. This dynamics is thoroughly analyzed by comparison with the results of the kinetic PIC MC simulations. The main processes that cause electron cooling have been revealed for two different time stages. The first afterglow stage is characterized by the rapid decrease of the electron temperature. During this stage, inelastic electron collisions with Ar atoms in the ground state play an important role in the electron cooling. During the second long-scale stage, only diffusion along the electron energy scale via Coulomb or elastic collisions can provide the observed effect of the gradual electron cooling. The effects of elastic and Coulomb collisions on the electron cooli...

    更新日期:2020-01-30
  • Spectroscopic investigation on the near-substrate plasma characteristics of chromium HiPIMS in low density discharge mode
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-28
    Xiao Zuo, Dong Zhang, Rende Chen, Peiling Ke, Magnus Odén and Aiying Wang

    High power impulse magnetron sputtering (HiPIMS) discharge promises high ionization fraction and energetic ions in comparison with dc magnetron sputtering discharge. But acknowledge on the characteristics of HiPIMS plasma in the near-substrate region (substrate vicinity), which is of great importance for film deposition, is still limited. Here, optical emission spectroscopy (OES) combined with the collisional-radiative modelling are developed and used to determine the electron temperature and the number density of neutral sputtered atom for the chromium HiPIMS plasma in substrate vicinity. The OES analysis demonstrated the HiPIMS discharge of Cr sputtering process in low density mode was dominated by the electron impact ionization of argon atoms and excitation of chromium atoms. As the HiPIMS plasma in the substrate vicinity is far from the local thermal equilibrium state, the relative intensities of transition lines to ArI 4 p states was used to calculate the electron tem...

    更新日期:2020-01-30
  • Understanding the ion acceleration mechanism in bipolar HiPIMS: the role of the double layer structure developed in the after-glow plasma
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-22
    Vasile Tiron and Ioana-Laura Velicu

    The physical vapor deposition techniques are nowadays widely used at industrial scale to produce thin films and surface coatings. Despite their proven utilities and benefits, these techniques still need to be improved in order to build other exigent and innovative coating systems, able to satisfy the market demand and to meet modern society’s needs. In this context, the bipolar high power impulse magnetron sputtering (BP-HiPIMS) technology is gaining ground and popularity due to its extraordinary ability to control the energy of the incoming ion flux to the growing film, enabling an energy-enhanced deposition process thanks to the existence of a dynamic double layer (DL) structure which develops in the after-glow plasma. In this work, the HiPIMS discharge was operated in bipolar mode, in which the negative pulses are followed by positive pulses whose amplitude, duration and delay can be independently controlled. The temporal and spatial evolutions of the plasma potential in BP-H...

    更新日期:2020-01-23
  • Extending the volume of atmospheric pressure plasma jets through the use of additional helium gas streams
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-22
    Michael J Johnson, David R Boris, Tzvetelina B Petrova and Scott G Walton

    Atmospheric pressure plasma jets are a promising tool for a variety of applications. However, the small size of atmospheric pressure plasma jets limits their use to small scale processes and materials treatment. To address this issue, this work describes how to increase the plasma volume without additional power supplies or circuitry. Instead, additional noble gas streams are positioned orthogonal to the jet’s direction of propagation which generates new plasma regions along these streams. This approach increases the plasma volume, which also increase the effective area available to interact with surfaces. The resulting augmented plasma is characterized with electrical, imaging, and time-integrated optical emission spectroscopy techniques. With these additional gas streams, the power required to drive the plasma jet increases sublinearly with the plasma volume, making this an attractive method to generate large area plasmas efficiently. The emission intensity of the He-air plasm...

    更新日期:2020-01-23
  • Diffuse vacuum arc with heated cathode made of ceramic (CeO 2 ) and metal (Cr) mixture
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-22
    R A Usmanov, R Kh Amirov, A V Gavrikov, G D Liziakin, A D Melnikov, V P Polistchook, I S Samoylov, V P Smirnov, N A Vorona and I M Yartsev

    The paper presents a diffuse vacuum arc with heated cathode made of ceramic (CeO 2 ) and metal (Cr) mixture, initiated and studied for the first time. Plasma sources of multicomponent mixtures are demanded for plasma based methods of rare-earths recycling and spent nuclear fuel reprocessing, which are currently under development. The discharge current–voltage characteristic was measured for different cathode temperatures (1950–2250 K); in the range of the arc current 30–100 A the voltage varied from 6 to 11 V. A cooling effect of the mixed cathode due to the thermionic emission at presence of the arc plasma was found; the effect reached about 150 W at the arc current of 30 A. The cooling effect and the current–voltage characteristic distinguish the discharge from the diffuse vacuum arcs with single-component cathodes made of cerium dioxide and chromium. The plasma parameters and optical emission spectra were analyzed for various cathode temperatures and arc currents (el...

    更新日期:2020-01-23
  • Inferring plasma parameters from the sheath characteristics of a dc biased hairpin probe
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-22
    A K Pandey, Jay K Joshi and S K Karkari

    In this paper, the cylindrical sheath around a hairpin resonator probe has been varied by applying a dc potential to the hairpin to infer different plasma parameters in an argon and oxygen discharge. As the sheath width increases due to negative bias, the resonance frequency of the hairpin correspondingly shifts toward a lower value. An analytical model based on fluid approximation has been developed to estimate the sheath width variation as a function of the applied voltage on the probe. The analytical result is then compared with the well-known capacitance model that assumes a conjugate dielectric region around the hairpin consisting of a pair of cylindrical sheaths and the plasma. Using this method, a wide range of plasma parameters, including the electron temperature ##IMG## [http://ej.iop.org/images/0963-0252/29/1/015009/psstab5695ieqn1.gif] {${T}_{e},$} plasma potential ##IMG## [http://ej.iop.org/images/0963-0252/29/1/...] {${V}_{p},$}

    更新日期:2020-01-23
  • Streamer breakdown: cathode spot formation, Trichel pulses and cathode-sheath instabilities
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-22
    Mirko Černák, Tomáš Hoder and Zdeněk Bonaventura

    The review provides an up-to-date overview and discussion of phenomena related to positive streamer breakdowns in short uniform and non-uniform field (corona) gaps. The terminology used to specify different types of streamer phenomena is critically discussed in light of a unified theory of high-pressure gas discharges describing the sequence of ionization events from initial electron avalanches up to a partial or complete breakdown. The emphasis is given to the understanding of the formation of an active cathode spot by the streamer arrival to the cathode, which is the critical but still obscure phase of the breakdown development. Based on the analysis including a computer simulation model a hypothesis is advanced that also such widely studied and practically important gas discharge phenomena as negative corona Trichel pulses and fast ionization instabilities in cathode regions of high-pressure gas discharges are due to the formation of positive streamers in the immediate cathod...

    更新日期:2020-01-23
  • Negative electric potential in a cylindrical plasma column with magnetized electrons
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-22
    G Liziakin, A Gavrikov and V Smirnov

    The possibility of creating adjustable electric fields in plasma opens up a wide range of applications for plasma technologies. However, the question with regards to the conditions, under which the plasma potential along the magnetic field line, resting on the electrode, repeats the potential of this electrode, turns out to be quite complex. In the present paper, an axially symmetric system with a magnetic field directed along an axis is considered. At the ends of the system, there are electrodes with a given negative potential. A simplified model of the system is proposed, taking into account the near-electrode voltage drop and continuity of the current in the circuit of the end electrodes. Within the framework of this model, an analytical formula is derived for the plasma potential on the axis of such a system, depending on its parameters. This formula can serve as a guide for experimenters when choosing experiment parameters, the purpose of which are to create a negative radi...

    更新日期:2020-01-23
  • Electron impact cross sections for carbon monoxide and their importance in the electron kinetics of CO 2 –CO mixtures
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-22
    Polina Ogloblina, Antonio Tejero-del-Caz, Vasco Guerra and Luís L Alves

    This work proposes a complete and consistent set of cross sections for electron impact collisions with carbon monoxide (CO), to be published in the IST-Lisbon database with LXCat. The set is validated by comparing swarm parameters calculated using the two-term Boltzmann solver LoKI-B with available experimental data. A severe inconsistency between the total rotational and effective cross sections reported in the literature for low values of the electron energy ( ϵ < 0.1 eV) is pointed out. It is shown that inelastic and superelastic collisions involving rotationally excited levels, as well as superelastic collisions with the first vibrational excited level, have to be taken into account to accurately calculate the electron energy distribution function. The relevance of these mechanisms implies a dependence of the effective momentum transfer cross section on the gas and vibrational temperatures and suggests its replacement by an elastic momentum transfer cross section. T...

    更新日期:2020-01-23
  • 更新日期:2020-01-23
  • Unstable electrostatic surface waves in a turbulent plasma containing streaming ions: transverse truncation approach
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2020-01-22
    Myoung-Jae Lee, Kazuo Takahashi and Young-Dae Jung

    The unstable modes of surface waves propagating in a sharply bounded turbulent plasma containing streaming ions are investigated by employing the specular reflection condition and the transverse truncation method. We have found that the bounded turbulent plasma supports damping and growing modes. The damping mode propagates for all values of the ion streaming speed modes and their behavior is similar to the case of surface waves in a turbulent plasma without ion streaming. If the speed of ion streaming is larger than the ion-acoustic speed, growing mode exists for all values of the wave number. However, if the ion stream is slower than the ion acoustic speed, then the growing mode appears under a certain condition. We derive the dispersion relations for such modes of surface waves and investigate the condition for propagation.

    更新日期:2020-01-23
  • Integrated effect on evolution of streamer dynamics under long-term repetitive sub-microsecond pulses in high-pressure nitrogen
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-12-18
    Z Zhao and J T Li

    Integrated effect and evolution of streamer dynamics were investigated under long-term repetitive sub-microsecond pulses (RMP) based on the pulse-sequence resolved electrical and optical measurements in 0.1–0.4 MPa nitrogen. New statistical methods were proposed for characterizing the discharge evolution process, including the repetitive working coefficient and the ‘sequence-phase-intensity-density’ diagram. A three-stage discharge evolution pattern is applicable for positive and negative RMP. A periodical feature of intermittent-mode corona discharges appears with increasing the pulse repetition frequency (PRF) under positive RMP, where the interval number increases and interval time gradually saturates with PRF. The breakdown occurs at high PRF following successive-mode corona discharges. The breakdown envelope curve consists of a rapidly falling stage followed by a saturation stage at low pressure or a rising stage at high pressure. Subsequent corona discharges are facilitate...

    更新日期:2019-12-19
  • He(2 3 S 1 ) and He 2 ( a 3 Σ u + ) metastables densities measured in an RF-driven helium plasma using broadband absorption spectroscopy
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-12-18
    Gaurav Nayak, Nader Sadeghi and Peter J Bruggeman

    Both atomic (He(2 3 S )) and molecular (He 2 ( a 3 Σ u + )) metastable species of helium are an important source of ionization in low electron density atmospheric pressure plasmas due to the efficient Penning ionization with impurities. In this contribution, we report for the first time the measured absolute densities of these metastable species in a capacitively coupled parallel plate atmospheric pressure helium glow discharge excited by radio frequency using broadband absorption spectroscopy. The spatial distribution profiles of these metastable species correlate well with RF-driven sheath structure operating in an α -mode regime. The peak density of He(2 3 S ) atoms at the sheath edge (∼6 × 10 18 m −3 ) is about 2.5 times larger than the peak density of He 2 ( a 3 Σ u + ) molecules at the same location. The study of the time-evolut...

    更新日期:2019-12-19
  • Extremely fast formation of anode spots in an atmospheric discharge points to a fundamental ultrafast breakdown mechanism
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-12-13
    E V Parkevich, M A Medvedev, A I Khirianova, G V Ivanenkov, A S Selyukov, A V Agafonov, K V Shpakov and A V Oginov

    By employing multi-frame laser interferometry, shadow, and schlieren imaging, we trace the formation of a nanosecond spark discharge in millimeter-sized air gaps formed by a point cathode and flat anode or vice-versa. We discover that the electrical breakdown of the discharge gap is associated with extremely fast (≪1 ns) explosive formation of micron-sized cathode and anode spots. We find that the characteristic delay between the instants of the anode and cathode spot initiation can be much shorter than 1 ns. The spots appear as highly ionized near-electrode plasmas with an electron density n e ∼ 10 19 –10 20 cm −3 . The spots then give rise to highly ionized spark channels with pronounced filamentary structures. Our findings indicate that the extremely fast formation of anode spots is associated with an ultrafast gap breakdown promoted by an ultrafast ionization wave (UFIW). The role of the UFIW governed by the rapidly evol...

    更新日期:2019-12-17
  • Discharge characterization of a multi-anode electrode geometry for vacuum arc thruster
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-12-13
    Weisheng Cui, Wenzheng Liu, Yongjie Gao and Xiuyang Chen

    Vacuum arc thrusters (VATs) have the potential to be used in nanosatellites and a multi-anode electrode geometry (MAEG) suitable for VATs is proposed in this paper. A unique electric field distribution is formed in the MAEG because of its anode configuration, which is different from conventional electrode geometry (CEG). There exists a region where the electric field vector has opposite directions in the electrode geometry. This region affects the directional drift of electrons in the initial stage of the discharge, thereby changing the process of vacuum breakdown. The variation of the discharge process affects the generation and propagation mechanism of the plasma, forming a plasma plume in favor of the propulsion performance of thrusters. The photographs of the plasma plume are captured and the electron density distributions are measured, which prove the pinch effect on the plasma plume of the MAEG. The propulsion performance of MAEG VATs is found to be superior to CEG VATs wi...

    更新日期:2019-12-17
  • Ionization wave propagation in an atmospheric pressure plasma multi-jet
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-12-13
    Amanda M Lietz, Xavier Damany, Eric Robert, Jean-Michel Pouvesle and Mark J Kushner

    The atmospheric pressure multi-plasma jet produces an array of individual plasma jets which originate from the branching of a single ionization wave (IW). The use of arrays of such plasma jets could enable treatment of larger surface areas than is possible with a single plasma jet. In this paper, we discuss results from a combined experimental and two-dimensional modeling investigation of the behavior of IWs in an atmospheric pressure plasma multi-jet device. In this multi-jet, a rare gas is flowed through a tube having a line of holes, producing gas jets into the ambient from each of the holes. A primary ionization wave (PIW) propagates through the tube which launches a series of secondary ionization waves (SIWs) propagating out each hole through the plumes of the individual gas jets. The propagation of the SIWs is more intense using a positive polarity voltage pulse due to the higher electric field at the ionization front. The diameter of the holes determines the delay of the ...

    更新日期:2019-12-17
  • Deterministic models of minority neutral particle kinetics close to a catalytic surface, based on the formalism of radiative transfer
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-12-13
    S Longo, G Micca Longo, E Pavone and F Schiavone

    The kinetics of neutral particles diluted in a gas or plasma and reacting with a catalytic surface can be calculated accurately only by taking into account the finite value of the mean free path. In reactor models, this problem is usually solved by using reaction-diffusion equations, but this approximation is not always appropriate. As an alternative, Monte Carlo (MC) simulations are used, but they are affected by the noxious problem of statistical error. We propose to address this problem by using the formalism of radiative transfer. A system of integral equations is formulated by generalizing the Schwarzschild–Milne one, in order to take into account several chemical species interacting with a partially catalytic surface, including any kind of backscattering angular distribution. We show that the generalized equations can be easily solved in a computer model using a standard relaxation technique; an excellent agreement with MC simulations is obtained. Applications are discusse...

    更新日期:2019-12-17
  • Experimental observation of interfacial oscillations and self-organization derived from streamer-driven mechanical perturbation of a gas–liquid boundary
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-12-10
    Janis Lai and John E Foster

    Plasma discharges in bubbles remain an active area of research because of the associated applications in environmental remediation, agriculture and chemical processing. Plasmas in contact with the gas–liquid interface can drive chemical and physical processes, one of which is the mechanical surface perturbation leading to the formation of capillary waves. Using a 2D discharge cell, capillary waves on the surface of a 2D bubble are investigated. This study reports the observation of interfacial capillary waves on the gas–liquid interface excited by nanosecond pulsed plasma discharges. The capillary waves appear to be initiated by streamers coming into contact with the interface, with surface tension playing the role of the restoring force and viscosity contributing to damping. The waves propagating along the bubble’s surface alter the bubble’s shape. This capillary wave mode was found to be dependent on bubble size and plasma pulse frequency. Sympathetic resonant oscillations wer...

    更新日期:2019-12-11
  • Steady-state simulation of different discharge modes of argon arc under external magnetic field
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-12-10
    Tang Chen and Han-Qiao Che

    In this study we performed a numerical investigation on different discharge modes of the magnetically rotating arc at atmospheric pressure. By using a three-dimensional simulation model taking into account of the arc-cathode interaction, it is able to predict the three different kinds of cathode arc attachments. Those modes of arc discharge have been observed in previous experiments. Arc attachments in constricted (i.e. spot) and diffuse mode are almost axisymmetric, however the edge mode offers a non-axisymmetric result. The corresponding arc plasma properties operating in different modes differ greatly from each other. Driven by the non-axisymmetric Lorentz force, a ‘twisted’ arc column emerges between the electrodes in edge mode, while the cathode arc attachment focuses to a corner of the edge. The heavy particle and electron particle temperatures are much lower in diffuse mode than the other two modes. Those plasma features of multi-modes should be considered in the applicat...

    更新日期:2019-12-11
  • Evolution of N( 4 S) atoms produced under nitrogen streamer conditions: time-resolved TALIF study at reduced pressures
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-12-10
    P Dvořák, M Šimek and V Prukner

    The evolution of N( 4 S) species produced by filamentary streamer discharge was investigated by two-photon absorption laser-induced fluorescence technique. A triggered single streamer filament was periodically produced in pure nitrogen at pressures of 20, 50, 100 and 200 Torr, and N( 4 S) species were monitored in the center of the discharge gap during the streamer formation, decay and afterglow. Under all of the investigated pressures, the population maxima of nitrogen atoms were observed in a microsecond timescale; i.e. well after the extinction of the streamer event. The concentration of nitrogen atoms increased with pressure. The maximum N( 4 S) concentration measured at 20 Torr was about 10 13 cm −3 , while it exceeded 10 15 cm −3 at 200 Torr. After reaching maxima, atomic densities exhibit hyperbolic decay, which was followed up to the post-discharge time of 0.5 ms. Our results show that only a small part of...

    更新日期:2019-12-11
  • Reillumination of submicrosecond pulsed corona-like discharges in water
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-12-10
    Raphael Rataj, Hans Höft and Juergen F Kolb

    Pronounced reilluminations can be observed for discharges that are generated in water by submicrosecond high-voltage pulses. This phenomenon can appear during the decrease of the applied voltage, depending on the pulse characteristics, especially fall times. The respective processes are expected to be crucial for optical investigations of discharge characteristics and also for applications. Accordingly, the development of individual corona-like discharges in water was investigated in a needle-to-plate geometry for their ignition by single rectangular high-voltage pulses with a duration of 100 ns. The pulse amplitudes of about 50 kV and adjusted pulse fall times of 20, 26, and 43 ns were used. Voltages, currents and light emissions were synchronized with subsequent images of individual discharge events. Two distinct stages, a propagation phase and a reillumination phase, were identified. The individual discharges expanded for all investigated fall times with the same velocity of ...

    更新日期:2019-12-11
  • Discharge characteristics and bactericidal mechanism of Ar plasma jet with ethanol and oxygen gas admixtures
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-12-10
    Wenjie Xia, Dingxin Liu, Li Guo, Weitao Wang, Han Xu, Chao Feng, Xiaohua Wang, Michael G Kong and Mingzhe Rong

    An argon plasma jet with gas admixtures of 0.2% ethanol (EtOH) and 0.08% oxygen, which has promising prospects in sterilization and anti-infection, is studied. EtOH can convert an argon plasma jet from filamentary mode into diffuse mode, as reported previously, and O 2 can further enhance its bactericidal effect dramatically. Compared to the Ar+EtOH plasma jet, the Ar+EtOH+O 2 plasma jet is still in diffuse mode, but its bactericidal effect increases by more than five orders of magnitude when used to treat Methicillin-resistant Staphylococcus aureus (MRSA) suspensions (∼1 × 10 8 CFU ml −1 ). Such a strong bactericidal effect can also be achieved by using deionized water activated by an Ar+EtOH+O 2 plasma jet, even when the plasma-activated water has been stored for 3 min before mixing with the MRSA suspension. This implies that some new antibacterial species are produced by the Ar+EtOH+O 2 plasma jet compared to t...

    更新日期:2019-12-11
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