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  • 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
  • Magnetic control of nonlinear electron resonance heating in a capacitively coupled radio frequency discharge
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-28
    M Oberberg, D Engel, B Berger, C Wölfel, D Eremin, J Lunze, R P Brinkmann, P Awakowicz and J Schulze

    In magnetized capacitively coupled radio frequency (RF) plasmas operated at low pressure, the magnetic asymmetry effect (MAE) provides the opportunity to control the discharge symmetry, the DC self-bias, and the ion energy distribution functions at boundary surfaces by adjusting a magnetic field, that is oriented parallel to the electrodes, at one electrode, while leaving it constant at the opposite electrode. This effect is caused by the presence of different plasma densities in regions of different magnetic field strength. Here, based on a balanced magnetron magnetic field configuration at the powered electrode, we demonstrate that the magnetic control of the plasma symmetry allows to tailor the generation of high frequency oscillations in the discharge current induced by the self-excitation of the plasma series resonance (PSR) through adjusting the magnetic field adjacent to the powered electrode. Experimental current measurements performed in an argon discharge at 1 Pa as we...

    更新日期:2019-11-29
  • Ion energy control via the electrical asymmetry effect to tune coating properties in reactive radio frequency sputtering
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-28
    Stefan Ries, Lars Banko, Marcus Hans, Daniel Primetzhofer, Jochen M Schneider, Alfred Ludwig, Peter Awakowicz and Julian Schulze

    A knowledge-based understanding of the plasma-surface-interaction with the aim to precisely control (reactive) sputtering processes for the deposition of thin films with tailored and reproducible properties is highly desired for industrial applications. In order to understand the effect of plasma parameter variations on the film properties, a single plasma parameter needs to be varied, while all other process and plasma parameters should remain constant. In this work, we use the Electrical Asymmetry Effect in a multi-frequency capacitively coupled plasma to control the ion energy at the substrate without affecting the ion-to-growth flux ratio by adjusting the relative phase between two consecutive driving harmonics and their voltage amplitudes. Measurements of the ion energy distribution function and ion flux at the substrate by a retarding field energy analyzer combined with the determined deposition rate R d for a reactive Ar/N 2 (8:1) plasma at 0.5...

    更新日期:2019-11-29
  • Benchmark calculations for electron velocity distribution function obtained with Monte Carlo Flux simulations
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-28
    L Vialetto, S Longo and P Diomede

    Modern, multi-modular plasma modeling requires accurate and versatile methods for the determination of the electron velocity distribution function from which rate coefficients of electron impact processes as well as electron transport quantities are determined. In this paper we propose as a solution a modified version of a strongly overlooked method developed in the early 90s, namely, Monte Carlo Flux (MCF). The improvement lies in a criterion for the otherwise somewhat empirical selection of the time-step used in the method. We show that an MCF based code highlights and overcomes the limitations of two-terms codes such as BOLSIG+ and it is much faster than a conventional Monte Carlo. Moreover, MCF is in excellent agreement with the multi-term method for a wide range of reduced electric fields, being at the same time much simpler to implement and to extend to more general cases than the latter. Explicit illustrations of the Markov matrices representing short-time kinetics are pr...

    更新日期:2019-11-29
  • Development of a semi-empirical 1.5D plasma fluid model for a single microdischarge in atmospheric pressure dielectric barrier discharges
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-28
    K-M Lin, Y-H Huang, W-Y Guo and Y-S Chang

    In this work, a semi-empirical 1.5D plasma fluid model (PFM) is proposed to model a single microdischarge (MD) in atmospheric pressure air dielectric barrier discharges (APADBDs). The species continuity equations and the electron energy density equation are solved in one-dimensional domain, while the Poisson equation is solved in the axisymmetric domain to capture the enhancement of the electric field in front of the streamer. The framework of air chemistry is considered and the effect of photoionization is modeled in the axisymmetric domain. The accumulation factor (AF) is introduced and determined by experimental data to model the accumulation of charged particles on the dielectric surface. The simulated results in two gaps are compared with experimental measurements. In the gap of 1.4 mm, the simulated electric current reaches 72 mA, which is close to the typically measured electric current. The simulated maximum wave velocity is around 1.7 × 10 6 m s −1 , ...

    更新日期:2019-11-29
  • Spatio-temporally resolved investigations of layered particle growth in a reactive argon-acetylene plasma
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-28
    Sebastian Groth, Franko Greiner and Alexander Piel

    The growth of nanometer-sized particle populations is studied in a reactive argon-acetylene plasma. Particular attention is paid to the spatio-temporal evolution of nested particle populations. For this purpose, a new non-invasive 2D imaging ellipsometry diagnostic is applied in combination with laser extinction measurements. In this way, the spatio-temporal evolution of particle size and density is obtained. The temporal evolution of the particle clouds during the first and subsequent growth cycles reveals a complex interplay between the different particle generations, the plasma and the resulting dust confinement. It is demonstrated that the electrostatic pressure needs to be considered in the force balance of systems with high dust densities. The relationship between the growth of particles and characteristic transition events visible in the dynamic of the void is discussed.

    更新日期:2019-11-29
  • Influence of collisions in a fluid model for the warm-ion sheath around a cylindrical Langmuir probe
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-28
    Guillermo Fernando Regodón, José Ignacio Fernández Palop, Juan Manuel Díaz-Cabrera and Jerónimo Ballesteros

    A long cylindrical Langmuir probe immersed in a collisional plasma is modelled by using fluid equations in which the collision term is introduced assuming a constant ion mean free path. The physical magnitudes of the system are expanded in a perturbation series in the collision parameter, that is, the ratio between the Debye length and the ion mean free path, and the system is thus separated into zeroth-order and first-order perturbation systems. The ion temperature is arbitrary and a continuous solution from the plasma to the probe is obtained for the perturbation systems. Using this methodology, a continuous solution for the ion sheath around a cylindrical Langmuir probe is obtained for long ion mean free path, for any ion temperature with no need of two-scale study or asymptotic matching. It is found that the collisions and the ion temperature have opposite effects, and these effects are quantified. The solution for cold ions cannot be obtained directly using this method, but...

    更新日期:2019-11-29
  • Characterization of CO 2 microwave plasma based on the phenomenon of skin-depth-limited contraction
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-28
    A J Wolf, T W H Righart, F J J Peeters, P W C Groen, M C M van de Sanden and W A Bongers

    The subatmospheric CO 2 microwave plasma is known to contract to a narrow filament with rising pressure as result of a mode transition. This changing state of contraction is investigated in relation to its dielectric properties, in order to directly relate the discharge parameters to the discharge radius. The electron density and gas temperature are measured, respectively, by 168 GHz microwave interferometry and Doppler broadening of the 777 nm oxygen emission lines. The plasma is operated in steady state with 1400 W at 2.45 GHz, between 100 mbar and 400 mbar. Electron density values in the central region range from 10 18 to 10 20 m −3 between the discharge modes, while the gas temperature increases from 3000 K to 6500 K, in good agreement with previously reported values. Based on the dielectric properties of the discharge in relation to the plasma radius, it is found that the discharge column constitutes a radius of a single skin depth. I...

    更新日期:2019-11-29
  • Influence of cold hollow cathode geometry on the radial characteristics of downstream magnetized plasma column
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-28
    M P Bhuva, S K Karkari and Sunil Kumar

    In this paper, the effect of cathode geometry on the radial characteristics of a downstream plasma column is presented for a cold cathode type of hollow cathode (HC) system. It is observed that when an axial magnetic field is applied to a cylindrical cathode, the downstream plasma exhibits an off-centered peak in the plasma density. However, as the magnetic field increases, the discharge extinguishes rapidly above a critical value, due to the suppression in secondary electron emission from the cylindrical cathode surface. On the other hand, by replacing the hollow cylinder with a cone-shaped cathode an oblique sheath is formed with respect to the axial magnetic field. This configuration helps in sustaining the discharge at twice the magnetic field than in the cylindrical case. It is also found that the downstream plasma exhibits a peak plasma density at the center for the case of the conical cathode. The above experimental observations for each HC setup has been qualitatively ex...

    更新日期:2019-11-29
  • Time-resolved optical emission spectroscopy of a unipolar and a bipolar pulsed magnetron sputtering discharge in an argon/oxygen gas mixture with a cobalt target
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-28
    R Hippler, M Cada, V Stranak and Z Hubicka

    Reactive high power impulse magnetron sputtering (HiPIMS) of a cobalt cathode in pure argon gas and with different oxygen admixtures was investigated by time-resolved optical emission spectroscopy (OES) and time-integrated energy-resolved mass spectrometry. The HiPIMS discharge was operated with a bipolar pulsed power supply capable of providing a large negative voltage with a typical pulse width of 100 μ s followed by a long positive pulse with a pulse width of about 350 μ s. The HiPIMS plasma in pure argon is dominated by Co + ions. With the addition of oxygen, O + ions become the second most prominent positive ion species. OES reveals the presence of Ar I, Co I, O I, and Ar II emission lines. The transition from an Ar + to a Co + ion sputtering discharge is inferred from time-resolved OES. The enhanced intensity of excited Ar +* ions is explained by simultaneous excitation and ionisation induced by energetic second...

    更新日期:2019-11-29
  • Controlling polarization of THz radiation in pair plasma
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-28
    Sheetal Punia and Hitendra K Malik

    Polarization-tunable terahertz (THz) radiation in pair plasma has been generated under the combined configuration of a helical wiggler and solenoidal magnetic fields. The control over the electromagnetic vector of the emitted field (i.e. polarization) furnishes the knob of another degree of freedom which is very useful in numerous applications. With the optimization of wiggler period and frequency, the total angular spread of the field has been reduced which provides a narrow-band THz spectrum. Additionally, the solenoidal field not only prevents the escape of particles during laser-matter interaction but also enhances the magnitude of emitted field. Along with the external magnetic field, collisions among the particles and ripples in plasma density have also been considered to fine-tune the radiation.

    更新日期:2019-11-29
  • A numerical analysis of a microwave induced coaxial surface wave discharge fed with a mixture of oxygen and hexamethyldisiloxane for the purpose of deposition
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-19
    Efe Kemaneci, Felix Mitschker, Jan Benedikt, Denis Eremin, Peter Awakowicz and Ralf Peter Brinkmann

    A microwave induced coaxial surface wave discharge with a feeding gas mixture of oxygen and hexamethyldisiloxane used for the deposition of polymer coatings is numerically analysed by a volume-averaged zero-dimensional modelling formalism. A set of edge-to-centre ratios are analytically estimated for a self-consistent description of the positive ion and reactive neutral flux at the radial walls (Kemaneci et al 2017 J. Phys. D: Appl. Phys. 50 245203). The simulation results are compared with the measurements of a wide variety of distinct particle concentrations as well as of the electron temperature and an agreement is obtained with respect to the input power, the pressure and the oxygen to hexamethyldisiloxane flow ratios. The net charge density is dominated by Si 2 OC 5 H ##IMG## [http://ej.iop.org/images/0963-0252/28/11/115003/psstab3f8aieqn1.gif] {${}_{15}^{+}$} with a negligible degree of electronegativity. Hexameth...

    更新日期:2019-11-19
  • Electric field determination from intensity ratio of ##IMG## [http://ej.iop.org/images/0963-0252/28/11/115011/toc_psstab3936ieqn1.gif] {${{\rm{N}}}_{2}^{+}$} and N 2 bands: nonequilibrium transient discharges in pure nitrogen
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-15
    Petr Bílek, Milan Šimek and Zdeněk Bonaventura

    We developed an extension of the spectrometric method to estimate a reduced electric field ( E / N ), which is applicable in nitrogen-containing plasmas. The method is based on the intensity ratio of the emission bands of the first negative system (FNS) of ##IMG## [http://ej.iop.org/images/0963-0252/28/11/115011/psstab3936ieqn3.gif] {${{\rm{N}}}_{2}^{+}$} and the second positive system (SPS) of N 2 . It uses the emission occurring in the wavelength interval 375–410 nm, which includes six SPS and two FNS bands. The choice of the spectral window is guided by much simpler acquisition and processing of experimental data than the SPS(0, 0) and FNS(0, 0) pair that is typically used. Following this idea, we construct a kinetic model for pure molecular nitrogen, which determines the population of the upper states responsible for the FNS and SPS emission. Moreover, we perform sensitivity analysis of the kinetic model, which allows us to reveal the...

    更新日期:2019-11-15
  • Diagnostics of low-temperature neon plasma through a fine-structure resolved collisional–radiative model
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-12
    S S Baghel, S Gupta, R K Gangwar and R Srivastava

    A collisional–radiative (CR) model for low-temperature Ne plasma is developed. Various radiative and collisional processes involving the ground 2 p 6 and the excited 2 p 5 3 s , 2 p 5 3 p , 2 p 5 3d , 2 p 5 4 s and 2 p 5 4 p states are considered in the plasma. First, we calculate a complete set of required electron-impact excitation cross-sections of Ne, which is an important process in such low-temperature plasma. We used the relativistic distorted wave (RDW) theory and calculated electron excitation cross-sections for the transitions from the ground 2 p 6 state to the excited 2 p 5 3 s , 2 p 5 3 p , 2 p 5 3d , 2 p 5 4 s and 2 p 5 4 p states, as well as from the excited state 2 p 5 3 s to t...

    更新日期:2019-11-13
  • Modified high frequency probe approach for diagnostics of highly reactive plasma
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-12
    Petr Sezemsky, Vitezslav Stranak, Jiri Kratochvil, Martin Cada, Rainer Hippler, Miroslav Hrabovsky and Zdenek Hubicka

    The paper introduces a modified approach of time resolved in situ diagnostics of highly reactive discharges (C 2 H 2 in our case) usually used for a deposition process of various non-conductive thin films. Reactive plasma could create an insulating film onto inserted diagnostic tools, which distorts measured data and makes their processing unreliable; a typical problem of Langmuir probe measurements. The proposed approach utilizes a so-called radiofrequency (rf) Sobolewski probe for ion flux measurement which is further modified to also obtain the electron temperature in some cases and the ion density. In this work, we introduce the procedure where measured rf probe characteristics are transformed towards I – V curves of the plasma sheath with subtracted capacitive current. This processing enables not only the monitoring of plasma sheath impedance and the ion flux towards the substrate but also allows for an estimation of other parameters as...

    更新日期:2019-11-13
  • 更新日期:2019-11-13
  • Experimental investigation of electron heating modes in capacitively coupled radio-frequency oxygen discharge
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-11
    S K Babu, S Kelly, S Kechkar, P Swift, S Daniels and M M Turner

    A Langmuir probe has been used to investigate electron heating mechanisms in a capacitively coupled oxygen discharge over a wide pressure range (50–800 mTorr) at a fixed applied power (200 W). Evidence presented here from experimentally obtained electron energy distribution functions (EEDFs) illustrates discharge transition from a collisionless (stochastic) to a collisional (Ohmic) dominant regime with increasing oxygen pressure. The discharge exhibited a bi-Maxwellian EEDF in the collisionless regime, dominated by stochastic heating whereas Druyvesteyn-like EEDFs were exhibited in the collisional dominant regime. Moreover, in the transition between these two regimes, parameters such as electron density, effective electron temperature and electron-neutral collision frequency exhibited significant variations.

    更新日期:2019-11-13
  • Macroscopical model of streamer coronas around a spherical electrode
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-11
    M González, F J Gordillo-Vázquez and A Luque

    We present a model for streamer coronas emerging from a spherical electrode at high electrostatic potential. By means of a macroscopic streamer model and approximating the corona as a set of identical streamers with a prescribed spatial distribution around the electrode, we establish that coronas more densely packed with streamers are slower and more efficient at screening the electric field inside the streamers. We also apply our model to investigate the electrostatic potential at the boundary of the corona sheath that surrounds a leader and we underline the relevance of the rise-time of the leader potential during a leader step.

    更新日期:2019-11-13
  • 3D numerical investigation of a free-burning argon arc with metal electrodes using a novel sheath coupling procedure
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-11
    P Liang and J P Trelles

    A novel coupling procedure describing the complicated plasma-electrode interaction process has been developed and applied into the 3D finite volume simulation of a direct current tungsten inert gas welding system. This is achieved by making the space charge layer (sheath) incorporated into the computation domain and interact with both bulk plasma and cathode through the effective electrical conductivity. Both chemical and thermal nonequilibrium phenomena as well as the self-induced magnetic fields have been taken into consideration by the model to ensure a realistic numerical description of a non-thermal arc. The applicability of this coupling procedure is further improved by calculating the real electric potential, which is capable of accounting for the effects of the complicated drift and diffusion processes. Numerical results of both 100 and 200 A discharge currents are presented, field reversal is obtained at near-anode regions in both cases, which is followed by the negativ...

    更新日期:2019-11-13
  • Optical properties of magnetized transient low-pressure plasma
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-08
    Roman Bergert and Slobodan Mitic

    A transient optically thick plasma under the influence of a constant external magnetic field was investigated taking self-absorption into account. Self-absorption which defines the excited state-densities is an important mechanism and can be used with other methods to describe the state densities for an optically thick plasma. This method is an established tool to retrieve state-density and plasma parameters. To measure each magnetic sub-level density of argon 1s 4 and 1s 5 (in Paschen’s notation) a tunable diode laser absorption spectroscopy was used. Based on reconstructed excited state densities, the self-absorption coefficient was calculated for individual magnetic sub-levels. A decrease in self-absorption with an external magnetic field was noticed indicating a higher transparency of the plasma. Furthermore a polarization dependent self-absorption was found. The presented results can help to model optical properties and interpret the absorption of a low-...

    更新日期:2019-11-11
  • Absolute CO number densities measured using TALIF in a non-thermal plasma environment
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-08
    M A Damen, D A C M Hage, A W van de Steeg, L M Martini and R Engeln

    We report first measurements of time-resolved absolute CO number densities and rotational temperatures in a non-thermal CO 2 plasma environment using TALIF with a nanosecond pulsed laser. Two-photon excitation spectra from the ##IMG## [http://ej.iop.org/images/0963-0252/28/11/115006/psstab496eieqn1.gif] {${B}^{1}{{\rm{\Sigma }}}^{+}$} ( v ′ =0) ← ##IMG## [http://ej.iop.org/images/0963-0252/28/11/115006/psstab496eieqn2.gif] {${X}^{1}{{\rm{\Sigma }}}^{+}$} ( v ″ = 0) Q-branch are recorded and fitted to extract rotational temperatures. Absolute number densities are determined from the frequency-integrated excitation spectrum. The plasma under investigation is a pulsed glow discharge operated at a frequency of 60 Hz with an plasma-on time of 5 ms per plasma cycle, 50 mA plasma current and a pressure of 6.67 mbar. CO number densities range from ##IMG## [http://ej.iop.or...] {$(2.6\pm 0.6)\times {10}^{22}$}

    更新日期:2019-11-11
  • Thermal induced NDC of electron swarms in N 2 and N 2 -like gases: the role of temperature and collision operator approximations
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-08
    M J E Casey, D G Cocks, G J Boyle, M J Brunger, S Dujko, J de Urquijo and R D White

    The role of temperature on the existence of negative differential conductivity (NDC) is investigated using Boltzmann equation calculations of electron swarms in gaseous nitrogen. This effect has been observed previously in both experimental results and calculations, with the important role of superelastic rotational collisional processes in this phenomenon being examined in this work. A simple analytic model cross-section set is employed to elucidate the role of de-excitation processes in NDC, with complementary physics identified in N 2 . The criterion of Robson (1984 Aust. J. Phys. 37 35) for predicting the occurrence of NDC using only knowledge of the collisional cross-sections is utilised for both the model system and N 2 , and found to be in excellent agreement with our simulated appearance of NDC. Finally, we also report on the impact of anisotropy in the very low threshold scattering channels on the transport coefficients, examine the finit...

    更新日期:2019-11-11
  • Numerical treatment of a magnetized electron fluid model within an electromagnetic plasma thruster simulation code
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-08
    J Zhou, D Pérez-Grande, P Fajardo and E Ahedo

    Plasma discharges in electromagnetic thrusters often operate with weakly-collisional, magnetized electrons. Macroscopic models of electrons provide affordable simulation times but require to be solved in magnetically aligned meshes so that large numerical diffusion does not ruin the solution. This work discusses suitable numerical schemes to solve the axisymmetric equations for the electric current continuity and the tensorial Ohm’s law in such meshes, when bounded by the thruster cylindrical or annular chamber. A finite volume method is appropriate for the current continuity equation, even when meshes present singular magnetic points. Finite differences and weighted least squares methods are compared for the Ohm‘s law. The last method is more prone to producing numerical diffusion and should be used only in the boundary cells and requires a special formulation in the boundary faces. In addition, the use of the thermalized potential is suggested for an accurate computation of pa...

    更新日期:2019-11-11
  • Interaction between a helium atmospheric plasma jet and targets and dynamics of the interface
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-11-08
    Luis Martinez, Akash Dhruv, Li Lin, Elias Balaras and Michael Keidar

    This paper investigates the interaction of a helium atmospheric plasma jet impinging onto liquid and metal targets using experimental and numerical techniques. The primary motivation of this study is to experimentally understand the effect of liquid and metal targets on the propagation of a plasma jet, and to numerically characterize chemical and electrical behavior at the plasma-water interface. This study is relevant in the ongoing research of plasma self-organization for the development of medical devices capable of self-adaptation. Experimental measurements are made to obtain ionization wave (IW) propagation, average electron density, and optical emission spectrum of the plasma near the interface for cases with copper and water targets and a freely expanding jet. The induced acidity on the plasma-treated water is measured by pH balance. Results confirm that both liquid and metal targets alter the IW propagation velocity and electric potential. IW average propagation speed is...

    更新日期:2019-11-11
  • High efficient plasma generation in an inductively coupled plasma using a passive resonant antenna
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-30
    Ju-Ho Kim, Young-Hun Hong and Chin-Wook Chung

    We developed a high efficiency plasma source in an inductively coupled discharge using a passive resonant antenna, which has the advantage that it could be retro-fitted to existing reactors with minimal change to the reactor. At the resonance, the source has a larger total equivalent resistance that is 3–18 times larger than that at the non-resonance. As the resistance increases at the fixed RF power, the RF current decreases accordingly, which indicates that the power loss in the powered antenna including the impedance matching circuits is significantly reduced. The experimental result shows that the power transfer efficiency is improved by about 30%–70% and the plasma density at the resonance increases 2–8 times higher than that at the non-resonance. For analysis, three-winding transformer model is developed. The experimental results are consistent with the model.

    更新日期:2019-11-01
  • Theoretical study of electron-induced vibrational excitation of NO 2
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-29
    Hainan Liu, Samantha Fonseca dos Santos, Chi Hong Yuen, Pietro Cortona, Viatcheslav Kokoouline and Mehdi Ayouz

    In this study, we compute cross sections for vibrational excitation of NO 2 ##IMG## [http://ej.iop.org/images/0963-0252/28/10/105017/psstab4b8aieqn1.gif] {$\left(X{}^{2}{A}_{1}\right)$} by electron impact. Calculations are performed using a theoretical approach based on a combination of the normal mode approximation for vibrational states of the target molecule, fixed-nuclei electron-NO 2 scattering matrices and the vibrational frame transformation employed to evaluate the scattering matrix for vibrational transitions. Thermally-averaged rate coefficients are derived from the obtained cross sections for temperatures in the 10–10000 K interval for excitation of each normal mode of the target molecule. Analytical fits for the rate coefficients for singlets and triplets are provided. In addition, a comprehensive set of calculations are performed for assessing the uncertainty of the present calculations. The uncertainty assessments indicate ...

    更新日期:2019-10-29
  • Manipulating the discharge pulse number in an atmospheric helium dielectric barrier discharge with multiple current pulses per half cycle
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-29
    Yuhui Zhang, Wenjun Ning, Dong Dai and Qiao Wang

    We report a systematic numerical study regarding the control of discharge pulse number in an atmospheric helium dielectric-barrier discharge with multiple current pulses per half cycle. The results indicated that by replacing the original sinusoidal applied voltage with a peak-levelled one, the manipulation of current pulse number in each discharge half cycle could be achieved, and the initial moment of flat-top stage t 0 , which reflects the duration of peak-levelled applied voltage, was set to be the controlling parameter. With the increase of flat-top duration, the current pulse number per half cycle decreased monotonously from the original value to zero. In this process, the current amplitude elevated, the peak phase delayed, and the energy efficiency in terms of electron production enhanced. Further analyses revealed that the above alterations in discharge performance were not caused by changes in seed electron level, but by the variations in discharge curr...

    更新日期:2019-10-29
  • Charge transfer equilibrium in surface barrier discharge: continuous current and negative ion-driven ionisation wave
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-29
    Tomáš Hoder, Petr Synek and Jan Voráč

    Sensitive measurements of very weak electrical currents in sinusoidally driven surface barrier discharge in atmospheric air are reported for discharge arrangements with and without liquid covering the top electrode. The transferred charge of the low-power discharge is carefully quantified and it is shown that after the complete voltage period the total charge balance is approaching zero. This rather obvious result is mechanically assumed in the literature, yet it is experimentally not understood in detail. We show that continuous and pulsed micro-ampere currents measured during the negative polarity are responsible for the gradual renewal of the charge transfer equilibrium abruptly distorted by strong electrical pulses caused by positive streamers during the opposite half-period. Using synchronised ICCD imaging we reveal that weak continuous current is caused by slowly expanding surface discharges stemming from previously established cathode spots. The expansion is caused by a s...

    更新日期:2019-10-29
  • Magnetic nozzle efficiency in a low power inductive plasma source
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-29
    T A Collard and B A Jorns

    The nozzle efficiency and performance of a magnetic nozzle operating at low power (<200 W) are experimentally and analytically characterized. A suite of diagnostics including Langmuir probes, emissive probes, Faraday probes, and laser induced fluorescence are employed to map the spatial distribution of the plasma properties in the near-field of a nozzle operated with xenon and peak magnetic field strengths ranging from 100 to 600 G. The nozzle efficiency is found to be <10% with plasma thrust contributions <120 μ N and specific impulse <35 s. These performance measurements are compared with predictions from quasi-1D idealized nozzle theory and found to be 50%–70% of the model predictions. It is shown that the reason for this discrepancy stems from the fact that the underlying assumption of the idealized model—that ions are sonic at the throat of the nozzle—is violated at low power operation. By correcting for the shifting location of the sonic transition point,...

    更新日期:2019-10-29
  • Spatial and temporal measurement of recombining detached plasmas by laser Thomson scattering
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-20
    Shin Kajita, Hiroshi Ohshima, Hirohiko Tanaka, Masamichi Seki, Hiroki Takano and Noriyasu Ohno

    Elucidation and control of the low temperature recombining plasmas under fusion relevant conditions are crucial issues. In this study, we applied a conditional average for laser Thomson scattering technique to measure the temporal evolution of the plasma instability in detached recombining plasmas in the divertor simulator NAGDIS-II. In recombining plasmas, it is shown that the electron energy distribution function has a non-Maxwellian component, and the fraction of the low electron temperature component increases with the gas pressure. It is found that one of the major reasons to cause the non-Maxwellian distribution function is in the temporal variations of the electron temperature. By using the conditional averaging method, the temporal evolutions of the spatial (vertical and radial) profiles of the electron density and temperature are revealed for different frequency ranges.

    更新日期:2019-10-21
  • Non-invasive in situ measurement of the near-wall ion kinetic energy in a magnetically shielded Hall thruster
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-20
    Sarah E Cusson, Benjamin A Jorns and Alec D Gallimore

    The ion velocity distribution functions in the near-wall region of a high-power, 9-kW class magnetically shielded Hall thruster are experimentally characterized to quantify the degree to which the discharge chamber walls are shielded from ion bombardment. Ion velocity measurements are performed at a discharge voltage of 300 V and a discharge current of 15 A using laser-induced fluorescence along the centerline and discharge chamber walls. The centerline results show that the location of the acceleration region exists downstream of the exit plane of the thruster, which is consistent with previous measurements on other magnetically shielded thrusters. Measurements performed in the near-wall region show that ions are moving approximately parallel to the walls up to the exit of the thruster; however, a small but finite maximum mean velocity of 0.2 km s −1 is directed toward the discharge chamber walls. A sheath analysis is performed to define a critical electron temperatur...

    更新日期:2019-10-21
  • Development and testing of an efficient data acquisition platform for machine learning of optical emission spectroscopy of plasmas in aqueous solution
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-20
    Ching-Yu Wang and Cheng-Che Hsu

    This study presents the development of an efficient data acquisition platform and discusses machine learning of optical emission spectroscopy (OES) of plasma in aqueous solution to demonstrate the multivariate analysis of spectra. A specially designed platform for efficient acquisition of spectra emanated from plasmas in solutions is developed, and several machine learning algorithms are tested for plasma analysis. This platform enables acquiring up to 10k spectra solutions with various pH values under constant solution conductivity, or vice versa, within 15 min. This rapid acquisition scheme provides a sufficient dataset for testing machine learning algorithms. We test the OES of plasmas ignited in solutions with designated conductivities with pH of 2.2–5.2. A total 40k spectra are collected and tested with principal component analysis (PCA) and an artificial neural network (ANN) to predict the conductivity of the solution. In PCA, the results show that most data points are ove...

    更新日期:2019-10-21
  • Turing patterns on a plasma-liquid interface
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-20
    Paul Rumbach, Alan E Lindsay and David B Go

    Radially symmetric patterns are observed in pin-to-plane DC plasma systems where a liquid solution is used as a planar resistive anode. The size and structure of these patterns depends on the plasma current and salt concentration of the liquid anode. We propose that these patterns initiate due to the reaction and diffusion of electrons in the anode sheath, where electron impact ionization serves as an autocatalytic reaction. The resulting system of reaction-diffusion equations is amenable to Turing stability analysis, which we use to theoretically predict the transition from a uniform plasma to a ring-shaped pattern state. Expressing the stability criteria in terms of plasma current and solution salt concentration, we derive a theoretical phase boundary for the onset of pattern formation, which is in excellent agreement with experimental results.

    更新日期:2019-10-21
  • Performance characterization of a low-power magnetically shielded Hall thruster with an internally-mounted hollow cathode
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-20
    Ryan W Conversano, Robert B Lobbia, Thomas V Kerber, Kimberlyn C Tilley, Dan M Goebel and Sean W Reilly

    Magnetically shielded miniature (MaSMi) is a low power (≤1 kW) long life (>100 kg Xe throughput) magnetically shielded Hall thruster that features an internally mounted hollow cathode. The development model MaSMi Hall thruster was designed, fabricated, and tested in preparation for advancement into an engineering model design. The MaSMi - DM uses an ultra-compact internally-mounted heaterless hollow cathode, which has previously demonstrated stable operation over a discharge current range of 0.5–4 A. More than 100 heaterless ignitions were performed during this test campaign, revealing consistent and predictable start-up behavior. Component testing of a novel anode manifold used in the MaSMi-DM demonstrated peak-to-peak azimuthal propellant flow distribution variations of less than 3.2% across three flow rates and two anodes. Current–voltage-magnetic field testing of the MaSMi-DM was completed over a discharge voltage range of 200–600 V, a discharge current range of 0.5–...

    更新日期:2019-10-21
  • 2D axial-azimuthal particle-in-cell benchmark for low-temperature partially magnetized plasmas
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-16
    T Charoy, J P Boeuf, A Bourdon, J A Carlsson, P Chabert, B Cuenot, D Eremin, L Garrigues, K Hara, I D Kaganovich, A T Powis, A Smolyakov, D Sydorenko, A Tavant, O Vermorel and W Villafana

    The increasing need to demonstrate the correctness of computer simulations has highlighted the importance of benchmarks. We define in this paper a representative simulation case to study low-temperature partially-magnetized plasmas. Seven independently developed particle-in-cell codes have simulated this benchmark case, with the same specified conditions. The characteristics of the codes used, such as implementation details or computing times and resources, are given. First, we compare at steady-state the time-averaged axial profiles of three main discharge parameters (axial electric field, ion density and electron temperature). We show that the results obtained exhibit a very good agreement within 5% between all the codes. As ##IMG## [http://ej.iop.org/images/0963-0252/28/10/105010/psstab46c5ieqn1.gif] {${\boldsymbol{E}}\times {\boldsymbol{B}}$} discharges are known to cause instabilities propagating in the direction of electron drift, an analysis of these...

    更新日期:2019-10-17
  • Observation of multiply charged states ions in a high-power pulsed reflex discharge
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-16
    Yu V Kovtun, A N Shapoval and Y V Siusko

    Time-resolved optical emission spectroscopy studies have been made to investigate the elemental/charge composition of the plasma ionic component at pulsed reflex discharge. The discharge plasma has are registered spectral lines neutral atoms and ions of the working gas Ar, Ar 1+ , Ar 2+ , and also of the cathode material: Zr, Zr 1+ , Zr 2+ , Zr 3+ . The presence of zirconium in the spectrum attests to the entry of cathode material into the plasma and its subsequent ionization. The variation of spectral line intensity with time in the early stage of the discharge and in the stage of dense plasma existence (time interval from the onset of the discharge up to 4 ms) correlates with the dynamics of plasma parameters. Characteristic times of appearance of excited atoms and ions in the plasma have been determined. The time of appearance of excited Zr* atoms is by the order of magnitude longer than that of Ar*. The stage of high-voltage mode ...

    更新日期:2019-10-17
  • Time- and space-resolved LIF measurement of the concentration of OH radicals generated by surface barrier discharge emerging from liquid water
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-16
    Jan Voráč, Petr Synek, Pavel Dvořák and Tomáš Hoder

    The concentration of OH radicals has been mapped in three-dimensions by scanning planar laser-induced fluorescence (LIF) in the vicinity of surface barrier discharge emerging from liquid water and propagating along a fused silica dielectric tube in argon. The concentration peaked in the region of active discharges near the water level at the value of 1.5 × 10 21 m −3 and decreased with the distance on a characteristic length of ∼0.4 mm, which suggests that the OH transport is dominated by diffusion. The OH production increases with power input ( P ) until it saturates for P > 0.75 W. It has been observed that the repetitive discharge appearance at preferred locations can be changed to stochastic (i.e. macroscopically homogeneous) by increasing the thickness of deionized water covering the earthed electrode.

    更新日期:2019-10-17
  • A general framework for photoionization calculations applied to nonthermal gas discharges in air
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-16
    R Janalizadeh and V P Pasko

    A general framework for photoionization rate calculations in a constant pressure gaseous medium is introduced. The formulation includes the number of photons emitted per unit volume per unit time per unit wavelength due to a radiating source, photobasorption cross sections and density of species comprising the medium, and the photoionization probability (i.e. photoionization yield) of the species being photoionized. We derive a standard integral representation of the photoionization problem that may be readily converted to a set of Helmholtz differential equations for efficient calculation of the photoionization rate. The model is applied to the photoionization problem in air in which ##IMG## [http://ej.iop.org/images/0963-0252/28/10/105006/psstab4374ieqn1.gif] {${b}^{1}{{\rm{\Pi }}}_{u}$} , ##IMG## [http://ej.iop.org/images/0963-0252/28/10/105006/psstab4374ieqn2.gif] {${{b}^{{\prime} }}^{1}{{\rm{\Sigma }}}_{u}^{+}$} , ##IMG##

    更新日期:2019-10-17
  • Numerical enhancements of the microwave resonant cavity method for plasma diagnostics
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-16
    J Faltýnek, V Kudrle, J Tesař, M Volfová and A Tálský

    Microwave resonator method is a well established and sensitive technique of plasma density measurements, especially in low pressure plasmas. The traditional Slater approximation of very small electromagnetic field perturbation is extended and corrected by a more accurate, yet relatively simple numerical model, also addressing further phenomena such as the resonator eigenmodes and the stability of the dominant mode. The presence of a discharge tube is found to be a main source of deviation from the Slater approximation. The pre-calculated numerical correction factors are directly applicable for a range of cavity and discharge tube geometries.

    更新日期:2019-10-17
  • A xenon collisional-radiative model applicable to electric propulsion devices: I. Calculations of electron-impact cross sections for xenon ions by the Dirac B-spline R-matrix method
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-06
    Yang Wang, Yan-Fei Wang, Xi-Ming Zhu, Oleg Zatsarinny and Klaus Bartschat

    A fully relativistic Dirac B-spline R-matrix (DBSR) method is applied to calculate the oscillator strengths and electron-impact excitation cross sections involving the 5s 2 5p 5 , 5s5p 6 , 5p 4 6s, 5p 4 5d, 5p 4 6p, and 5p 4 7s states of a Xe + ion. A fully relativistic approach is necessary for this problem, since the spin–orbit coupling is of the same order as electron correlations in the outer shells of Xe + . Also, there is a complex open-shell structure with strong term dependence in the one-electron orbitals. The oscillator strengths are also calculated and agree well with available experimental measurements. We select some important excitation cross sections out of the ground, metastable, and quasi-metastable states of Xe + for the collisional-radiative (CR) model to be discussed and analyzed. The present paper is the first one of a series of studies on a CR model of xenon ions in ...

    更新日期:2019-10-07
  • A xenon collisional-radiative model applicable to electric propulsion devices: II. Kinetics of the 6 s , 6 p , and 5 d states of atoms and ions in Hall thrusters
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-06
    Xi-Ming Zhu, Yan-Fei Wang, Yang Wang, Da-Ren Yu, Oleg Zatsarinny, Klaus Bartschat, Tsanko Vaskov Tsankov and Uwe Czarnetzki

    Electric propulsion devices of using xenon propellant are nowadays widely adopted for the space missions. A collisional-radiative (CR) model of xenon needs to be developed to understand the kinetic mechanisms of the excited and energetic species in these devices and also to support their optical diagnostics. Previously, due to limitations in the fundamental cross section data, Xe CR models focused on the atomic species; the ionic species, which also play important roles for the thrusters, were not studied in detail. In our previous paper, a fully relativistic Dirac B -spline R -matrix method was applied to calculate the relevant cross sections for electron collisions with the Xe + ion. Based on these data, a comprehensive CR model—with the kinetics of metastable and excited levels of both Xe and Xe + included—could be built. The calculated density distributions of atomic and ionic levels are examined by optical measurements in Hall thrusters in al...

    更新日期:2019-10-07
  • Review on experimental and theoretical investigations of the early stage, femtoseconds to microseconds processes during laser ablation in liquid-phase for the synthesis of colloidal nanoparticles
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-06
    A Kanitz, M-R Kalus, E L Gurevich, A Ostendorf, S Barcikowski and D Amans

    Laser ablation in liquid-phase (LAL) has been developed since the 1990s, but the interest in laser synthesis of colloids has emerged in the last decade due to a significant improvement in the production rate, proven comparative advantages in biomedical and catalysis applications, and recent commercialization. However, the method relies on highly transient phenomena, so that the fundamental understanding lacks behind the LAL synthesis refinement research. The complexity of the physics and chemistry involved has led to experimental and theoretical investigations that attempt to provide a basic description of the underlying processes but face the challenge of temporal and spatial resolution as well as non-equilibrium conditions. It appears that the processes occurring at the early time scales, ranging from femtoseconds to several microseconds are critical in the definition of the final product. The review is mainly dedicated to the comprehensive description of the processes occurri...

    更新日期:2019-10-07
  • An experimental study of a dual-stage 4-grid ion thruster
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-10-02
    Lianjun Jia, Le Yang, Yong Zhao, Mingzheng Liu, Yanhui Jia, Tianping Zhang, Jianhong Zhuang, Fuquan Yang, Yide Zhao and Xianming Wu

    Performance experiments of the dual-stage 4-grid ion thruster were conducted. Experimental results showed that the specific impulse reached 7100 s and the beam divergence angle reached 6.3° when the screen and extraction potentials were 4.5 and 2.5 kV, respectively. The test results of beam extraction characteristics showed that the extraction capacity of ions was determined by extraction potential and was independent of screen grid and acceleration stage potentials. The extraction capacity of ions was analyzed with plasma sheath theory, and conclusions were in accordance with the experimental results. This study presents the decoupling mechanism of ion extraction and acceleration processes of the dual-stage ion 4-grid optical system by experiment and simulation.

    更新日期:2019-10-03
  • Determination of water leaks flows and their surface localization in plasma reactors by the ratio of the hydrogen isotopes line intensities
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-09-30
    A V Bernatskiy, I V Kochetov and V N Ochkin

    A high sensitive method of multispectral actinometry developed for the measurements of the concentration of minor hydrogen-oxygen products of plasma-chemical transformation of water is presented. It is shown that in presence of deuterium the correlation between H / D density ratio and the densities of other products is practically independent of non-equilibrium plasma conditions. It was studied in the hollow cathode experimental installation and model of the processes was developed for scaling purposes. This method allows to find the sources of water leaks to plasma due to the chamber wall defects and to measure their flow rates. The penetration of water vapors into the model installation was provided with a special localized leak and H / D ratio was measured by D α and H α lines intensity. The scaling was performed for the specific conditions of ITER reactor near-wall plasma during testing trials. The flows of the Н

    更新日期:2019-10-01
  • Convenient analytical solution for vibrational distribution function of molecules colliding with a wall
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-09-30
    Wei Yang, Alexander V Khrabrov, Igor D Kaganovich and You-Nian Wang

    We study formation of the Vibrational Distribution Function (VDF) in a molecular gas at low pressure, when vibrational levels are excited by electron impact and deactivated in collisions with walls and show that this problem has a convenient analytical solution that can be used to obtain VDF and its dependence on external parameters. The VDF is determined by excitation of vibrational levels by an external source and deactivation in collisions with the wall. Deactivation in wall collisions is little known process. However, we found that the VDF is weakly dependent on the functional form of the actual form of probability ##IMG## [http://ej.iop.org/images/0963-0252/28/10/10LT01/psstab4310ieqn1.gif] {${\gamma }_{\upsilon ^{\prime} \to \upsilon }$} for a vibrational number ##IMG## [http://ej.iop.org/images/0963-0252/28/10/10LT01/psstab4310ieqn2.gif] {$\upsilon ^{\prime} $} to transfer into a lower level ##IMG## {$\upsilon $}

    更新日期:2019-10-01
  • Magnetoplasmadynamic two-stage micro-cathode arc thruster for CubeSats
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-09-30
    D B Zolotukhin, K P Daniels, S R P Bandaru and M Keidar

    The addition of the acceleration stage to a micro-cathode vacuum arc thruster ( μ CAT) increases the thrust and the specific impulse. This improves the control of small satellites’ orbital parameters and, therefore, the overall efficiency of this thruster for CubeSats. In this article, we show that the second accelerating stage based on the magnetoplasmadynamic (MPD) approach allows improvements not only to the thrust (almost twice, from 9 to 18 μ N), but the thrust-to-power ratio (in 53%, from 3.2 to 4.9 μ N W −1 ) of the low-power (several W) miniature (several cm—size) μ CAT, firing at a pulse repetition rate of 10 Hz. A significant advantage of the μ CAT-MPD approach is the griddle construction, a design that helps to overcome the loss of ions along the grid cells in the case of gridded ion acceleration stage.

    更新日期:2019-10-01
  • Two-dimensional temperature distribution of air arc commutating to arc runner
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-09-23
    Akiko Kumada, Taiga Nagata, Kunihiko Hidaka, Shinya Watanabe and Kentaro Kokura

    Molded case circuit breakers (MCCBs) are used to provide overcurrent and short-circuit protection for low-voltage devices with rated currents of several hundreds of amperes. In MCCBs, some arc discharges have been observed to remain on the contacts and hardly move to the arc runners. Information about the temperature distribution over an air arc plasma is indispensable in investigating and clarifying such arc-commutation phenomena. We propose a new optical system that enables dynamic measurement of the two-dimensional temperature distribution over air arc via the two-line radiance ratio method. The system consists of a four hold-lens array, a high-speed video camera, and interference filters whose wavelengths correspond to the emission spectra of air arcs with metallic vapor. The dynamics of the air arcs in a mock MCCB was measured with this system. The anode root commutates to the runner, where its ambient temperature exceeds threshold T th , by contrast, there...

    更新日期:2019-09-25
  • Control of charged particle dynamics in capacitively coupled plasmas driven by tailored voltage waveforms in mixtures of Ar and CF 4
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-09-23
    S Brandt, B Berger, Z Donkó, A Derzsi, E Schüngel, M Koepke and J Schulze

    The charged-particle power absorption dynamics in capacitively coupled plasmas operated in different CF 4 -Ar gas mixtures and driven by tailored voltage waveforms is experimentally investigated by phase-resolved optical emission spectroscopy in conjunction with kinetic simulations and an analytical model. Single- and triple-frequency ‘peaks’- and ‘valleys’-type waveforms (generated as a superposition of multiple consecutive harmonics of 13.56 MHz) are studied at pressures of 20 and 60 Pa with 25 mm electrode gap and 150 V total driving voltage amplitude to determine the effects of the tailored driving voltage waveform in different gas mixtures on the density profiles of the particle species, the electronegativity, the DC self-bias, and the excitation/ionization dynamics. As the argon content in the buffer gas is increased, the discharge switches from the drift-ambipolar (DA) power absorption mode to the α -mode. This transition occurs due to the disappearance of ...

    更新日期:2019-09-25
  • Enhancement of Ohmic heating by Hall current in magnetized capacitively coupled discharges
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-09-23
    Bocong Zheng, Keliang Wang, Timothy Grotjohn, Thomas Schuelke and Qi Hua Fan

    In low-pressure capacitively coupled discharges, a heating mode transition from a pressure-heating dominated state to an Ohmic-heating dominated state is known by applying a small transverse magnetic field. Here we demonstrate via particle-in-cell simulations and a moment analysis of the Boltzmann equation that the enhancement of Ohmic heating is induced by the Hall current in the ##IMG## [http://ej.iop.org/images/0963-0252/28/9/09LT03/psstab419dieqn1.gif] {${\boldsymbol{E}}\times {\boldsymbol{B}}$} direction. As the magnetic field increases, the Ohmic heating in the ##IMG## [http://ej.iop.org/images/0963-0252/28/9/09LT03/psstab419dieqn2.gif] {${\boldsymbol{E}}\times {\boldsymbol{B}}$} direction dominates the total electron power absorption. The Ohmic heating induced by the Hall current can be well approximated from the Ohmic heating of unmagnetized capacitively coupled discharges.

    更新日期:2019-09-25
  • Dissipated electrical power and electron density in an RF atmospheric pressure helium plasma jet
    Plasma Sources Sci. Technol. (IF 4.128) Pub Date : 2019-09-23
    J Golda, F Kogelheide, P Awakowicz and V Schulz-von der Gathen

    Atmospheric pressure plasmas have great potential, especially for biomedical applications, due to the large number of reactive species produced. In particular with regard to these applications, the comparability of processes through appropriate control of plasma parameters is essential for treatment safety. Here we present a method for the operando determination of absolute absorbed power in an RF atmospheric pressure helium plasma discharge using miniaturized probes. A detailed error analysis demonstrates the reliability of the measured power values. With the help of a global model, the sheath width and electron density (4 × 10 16 –11 × 10 16 m −3 ) are derived from these power measurements and compared to literature. The results and thus the validity of the electrical model are confirmed by a second, independent characterization method using optical emission spectroscopy and time-averaged imaging.

    更新日期:2019-09-25
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