Fluid simulation of the effect of a dielectric window with high temperature on plasma parameters in inductively coupled plasma

To maintain the high-density plasma source in inductively coupled plasma (ICP), very high radiofrequency power is often delivered to the antenna, which can heat the dielectric windows near the antenna to high temperature. This high temperature can modulate the plasma characteristics to a large degree. We thus study the effect of dielectric window temperature on plasma parameters in two different ICP structures based on COMSOL software. The distributions of various plasma species are examined at different dielectric window temperatures. The concentration of neutral gas is found to be largely modulated at high dielectric window temperature, which further affects the electron collision probability with neutrals and the electron temperature. However, the electron density profiles are barely affected by the dielectric window temperature, which is mainly concentrated at the center of the reactor due to the fixed power input and pressure.     

Study of electron-extraction characteristics of an inductively coupled radio-frequency plasma neutralizer

Inductively coupled radio-frequency (RF) plasma neutralizer (RPN) is an insert-free device that can be employed as an electron source in electric propulsion applications.Electron-extraction characteristics of the RPN are related to the bulk plasma parameters and the device's geometry.Therefore,the effects of different electron-extraction apertures and operational parameters upon the electron-extraction characteristics are investigated according to the global nonambipolar flow and sheath model.Moreover,these models can also be used to explain why the electron-extraction characteristics of the RPN strongly depend upon the formation of the anode spot.During the experimental study,two types of anode spots are observed.Each of them has unique characteristics of electron extraction.Moreover,the hysteresis of an anode spot is observed by changing the xenon volume-flow rates or the bias voltages.In addition,the rapid ignited method,gas-utilization factor,electron-extraction cost and other factors that need to be considered in the design of the RPN are also discussed.     

Effect of single-legged coil on 3D plasma boundary corrugation in EAST

A single-legged coil behind the lower divertor and covering a 120° toroidal angle is utilized in a recent EAST discharge,for the purpose of increasing the wetted area of the divertor surface by locally modifying the magnetic field near the X-point.The plasma response,in particular,the plasma boundary surface corrugation due to the single-legged coil current,is modeled by the updated MARS-F code,by computing the plasma displacement for all important toroidal harmonics (n =1,2,4 and 5) associated with the partial toroidal coverage by the coil.The plasma response produced by the single-legged coil is found to be non-local and is of the kink-peeling type.For a reference EAST plasma with a lower single-null magnetic configuration,the plasma boundary corrugation near the X-point,produced by the upper single-legged coil,is about twice as large as that produced by the lower single-legged coil,despite the proximity of the latter to the X-point.     

感应耦合等离子体源制备硬质类金刚石膜的研究

采用感应耦合等离子体源(ICPS)成功地实现化学气相沉积硬质类金刚石(DLC)膜,并考察了基片负偏压对类金刚石膜沉积过程和薄膜性质的影响。薄膜的微观形貌、显微硬度、沉积速率以及结构成分分析表明感应耦合等离子体源适于制备硬质类金刚石膜,并且在相对较低的基片负偏压条件就可以获得高硬度的类金刚石膜。基片负偏压对类金刚石膜化学气相沉积过程和薄膜性质都有显著影响。     

Tunable triangular and honeycomb plasma structures in dielectric barrier discharge with mesh-liquid electrodes

We demonstrate a method to generate tunable triangular and honeycomb plasma structures via dielectric barrier discharge with uniquely designed mesh-liquid electrodes. A rapid reconfiguration between the triangular lattice and honeycomb lattice has been realized. Novel structures comprised of triangular plasma elements have been observed and a robust angular reorientation of the triangular plasma elements withis suggested. An active control on the geometrical shape, size and angular orientation of the plasma elements has been achieved. Moreover, the formation mechanism of different plasma structures is studied by spatial-temporal resolved measurements using a high-speed camera. The photonic band diagrams of the plasma structures are calculated by use of finite element method and two large omnidirectional band gaps have been obtained for honeycomb lattices, demonstrating that such plasma structures can be potentially used as plasma photonic crystals to manipulate the propagation of microwaves. The results may offer new strategies for engineering the band gaps and provide enlightenments on designing new types of 2D and possibly 3D metamaterials in other fields.     

电感耦合等离子体质谱法测定硼同位素丰度

以硼同位素标准参考物质NIST SRM 951配制的标准溶液,在优化的操作条件下对电感耦合等离子体质谱(ICP-MS)测定的硼同位素质量进行校正,求出校正因子,确定了样品的线性浓度范围.在同样的仪器条件下测定了硼同位素浓缩过程中样品三氟化硼甲醚络合物中的硼同位素丰度比,测定结果的相对标准偏差为1.095%.此外考查了仪器的稳定性.实验结果表明,本文建立的测定硼同位素丰度的方法"记忆效应"小,结果可靠,测量精度高.     

Effects of O2 addition on the plasma uniformity and reactivity of Ar DBD excited by ns pulsed and AC power supplies

Dielectric barrier discharges (DBDs) have been widely used in ozone synthesis, materials surface treatment, and plasma medicine for their advantages of uniform discharge and high plasma-chemical reactivity. To improve the reactivity of DBDs, in this work, the O₂ is added into Ar nanosecond (ns) pulsed and AC DBDs. The uniformity and discharge characteristics of Ar ns pulsed and AC DBDs with different O₂ contents are investigated with optical and electrical diagnosis methods. The DBD uniformity is quantitatively analyzed by gray value standard deviation method. The electrical parameters are extracted from voltage and current waveforms separation to characterize the discharge processes and calculate electron density n_e. The optical emission spectroscopy is measured to show the plasma reactivity and calculate the trend of electron temperature T_e with the ratio of two emission lines. It is found that the ns pulsed DBD has a much better uniformity than AC DBD for the fast rising and falling time. With the addition of O₂, the uniformity of ns pulsed DBD gets worse for the space electric field distortion by O₂⁻, which promotes the filamentary formation. While, in AC DBD, the added O₂ can reduce the intensity of filaments, which enhances the discharge uniformity. The ns pulsed DBD has a much higher instantaneous power and energy efficiency than AC DBD. The ratio of Ar emission intensities indicates that the T_e drops quickly with the addition of O₂ both ns pulsed and AC DBDs and the ns pulsed DBD has an obvious higher T_e and n_e than AC DBD. The results are helpful for the realization of the reactive and uniform low temperature plasma sources.     

The features of band structures for woodpile three-dimensional photonic crystals with plasma and function dielectric constituents

The features of the band structures of woodpile three-dimensional (3D) photonic crystals composed of plasma and function dielectric constituents, referred to as function plasma photonic crystals (FPPCs), are theoretically studied by a modified plane wave expansion method, and the formulas for computing the band structures are derived. The arrangement for the proposed FPPCs is that the function dielectric columns are surrounded by plasma, and the embedded dielectric columns are stacked according to the woodpile lattices, which are arrayed with face- centered-tetragonal symmetry. The relative permittivity of function dielectric rods depends on the function coefficient and space coordinates. The relationships between the parameters for inserted function dielectric rods and plasma and the band structures are also investigated. The computed results illustrate that the obtained PBG can be tuned by those parameters as mentioned above. Compared to dielectric–air PCs, function dielectric PCs and plasma dielectric PCs with the same topology, a wider bandwidth of the photonic band gap can be observed in the proposed FPPCs. The calculated results also show us another alternative way to realize reconfigurable applications with 3D FPPCs.     

Characteristics of inductively coupled plasma(ICP) and helicon plasma in a singleloop antenna

Large area uniform plasma sources, such as high-density magnetized inductively coupled plasma(ICP) and helicon plasma, have broad applications in industry. A comprehensive comparison of ICP and helicon plasma, excited by a single-loop antenna, is presented in this paper from the perspectives of mode transition, hysteresis behavior, and density distribution. The E-H mode transition in ICP and the E-H-W mode transition in helicon plasma are clearly observed in the experiments. Besides, the considerable variation of hysteresis behavior from inverse hysteresis to normal hysteresis by the influence of the magnetic field is explored. The bi-Maxwellian and Maxwellian electron energy distribution functions in each discharge are used to explain this phenomenon, which is essentially related to the transition from a nonlocal kinetic property to a local kinetic property of electrons. In addition, we notice that the plasma density, in the radial direction, is peaked in the center of the tube in ICP, but a complicated distribution is formed in helicon plasma. In the axial direction, the maximum plasma density is still in the center of the antenna in ICP, whereas the highest plasma density is located downstream, far away from the antenna, in helicon plasma. It is believed that the reflected electrons in the sheath and pre-sheath by the upper metallic endplate and downstream propagated helicon wave will be responsible for this plasma density profile in helicon plasma. Due to the constrained electron motion in the magnetic field, an extremely uniform density distribution will be obtained with an appropriate axial magnetic field in the wave discharge mode.     

Experimental investigation of the electromagnetic effect and improvement of the plasma radial uniformity in a large-area,very-high frequency capacitive argon discharge

We performed an experimental investigation on the electromagnetic effect and the plasma radial uniformity in a larger-area, cylindrical capacitively coupled plasma reactor. By utilizing a floating hairpin probe, dependences of the plasma radial density on the driving frequency and the radio-frequency power over a wide pressure range of 5–40 Pa were presented. At a relatively low frequency(LF, e.g. 27 MHz), an evident peak generally appears near the electrode edge for all pressures investigated here due to the edge field effect, while at a very high frequency(VHF, e.g.60 or 100 MHz), the plasma density shows a sharp peak at the discharge center at lower pressures, indicating a strong standing wave effect. As the RF power increases, the center-peak structure of plasma density becomes more evident. With increasing the pressure, the standing wave effect is gradually overwhelmed by the ‘stop band' effect, resulting in a transition in the plasma density profile from a central peak to an edge peak. To improve the plasma radial uniformity, a LF source is introduced into the VHF plasma by balancing the standing wave effect with the edge effect. A much better plasma uniformity can be obtained if one chooses appropriate LF powers, pressures and other corresponding discharge parameters.     

Frequency dependence of plasma characteristics at different pressures in cylindrical inductively coupled plasma source

The effects of driving frequency on plasma parameters and electron heating efficiency are studied in cylindrical inductively coupled plasma (ICP) source. Measurements are made in an Ar discharge for driving frequency at 13.56/2 MHz, and pressures of 0.4–1.2 Pa. In 13.56 MHz discharge, higher electron density (n_e) and higher electron temperature (T_e) are observed in comparison with 2 MHz discharge at 0.6–1.2 Pa. However, slightly highern_e andT_e are observed in 2 MHz discharge at 0.4 Pa. This observation is explained by enhanced electron heating efficiency due to the resonance between the oscillation of 2 MHz electromagnetic field and electron-neutral collision process at 0.4 Pa. It is also found that the variation ofT_e distribution is different in 13.56 and 2 MHz discharge. For ICP at 13.56 MHz, T_e shows an edge-high profile at 0.4–1.2 Pa. For 2 MHz discharge,T_e remains an edge-high distribution at 0.4–0.8 Pa. However, the distribution pattern involves into a center-high profile at 0.9–1.2 Pa. The spatial profiles ofn_e remain a center-high shape in both 13.56 and 2 MHz discharges, which indicates the nonlocal kinetics at low pressures. Better uniformity could be achieved by using 2 MHz discharge. The effects of gas pressure on plasma parameters are also examined. An increase in gas pressure necessitates the rise ofn_e in both 13.56 and 2 MHz discharges. Meanwhile, T_e drops when gas pressure increases and shows a flatter distribution at higher pressure.     

1d3v PIC/MCC simulation of dielectric barrier discharge dynamics in hydrogen sulfide

In this study, we computationally examined the dynamics of dielectric barrier discharge in hydrogen sulfide. The simulations were performed with a 1d3v particle-in-cell/Monte Carlo collision model in which a parallel-plate electrode geometry with dielectrics was used. Particle recombination process is represented in the model. The discharge mode was found to be initially Townsend discharge developing from the cathode to the anode, and at the peak of the current, a more stable glow discharge develops from the anode to the cathode. A higher applied voltage results in sufficient secondary electrons to trigger a second current peak, and then the current amplitude increases. As the frequency is increased, it leads to the advance of the phase and an increase in the amplitude of the current peak. A higher dielectric permittivity also makes the discharge occur earlier and more violently in the gap.     

High-efficiency removal of NO_x using dielectric barrier discharge nonthermal plasma with water as an outer electrode

With the rapid increase in the number of cars and the development of industry, nitrogen oxide(NO_x)emissions have become a serious and pressing problem. This work reports on the development of a water-cooled dielectric barrier discharge reactor for gaseous NOxremoval at low temperature. The characteristics of the reactor are evaluated with and without packing of the reaction tube with 2 mm diameter dielectric beads composed of glass, ZnO, MnO_2, ZrO_2, or Fe_2O_3. It is found that the use of a water-cooled tube reduces the temperature, which stabilizes the reaction, and provides a much greater NO conversion efficiency(28.8%) than that obtained using quartz tube(14.1%) at a frequency of 8 k Hz with an input voltage of 6.8 k V. Furthermore,under equivalent conditions, packing the reactor tube with glass beads greatly increases the NO conversion efficiency to 95.85%. This is because the dielectric beads alter the distribution of the electric field due to the influence of polarization at the glass bead surfaces, which ultimately enhances the plasma discharge intensity. The presence of the dielectric beads increases the gas residence time within the reactor. Experimental verification and a theoretical basis are provided for the industrial application of the proposed plasma NO removal process employing dielectric bead packing.     

Study on the RF inductively coupled plasma spheroidization of refractory W and W-Ta alloy powders

Spherical powders with good flowability and high stacking density are mandatory for powder bed additive manufacturing. Nevertheless, the preparation of spherical refractory tungsten and tungsten alloy powders is a formidable task. In this paper, spherical refractory metal powders processed by high-energy stir ball milling and RF inductively coupled plasma were investigated.By utilizing the technical route, pure spherical tungsten powders were prepared successfully, the flowability increased from 10.7 s/50 g to 5.5 s/50 g and apparent density increased from6.916 g cm~(-3) to 11.041 g cm~(-3). Alloying element tantalum can reduce the tendency to microcrack during tungsten laser melting and rapid solidification process. Spherical W-6 Ta(%wt)powders were prepared in this way, homogeneous dispersion of tantalum in a tungsten matrix occurred but a small amount of flake-like shape particles appeared after high-energy stir ball milling. The flake-like shape particles can hardly be spheroidized in subsequent RF inductively coupled plasma process, might result from the unique suspended state of flaky particles under complex electric and magnetic fields as well as plasma-particle heat exchange was different under various turbulence models. As a result, the flake-like shape particles cannot pass through the high-temperature area of thermal plasma torch and cannot be spheroidized properly.     

Experimental and simulation investigation of electrical and plasma parameters in a low pressure inductively coupled argon plasma

The electrical and plasma parameters of a low pressure inductively coupled argon plasma are investigated over a wide range of parameters(RF power, flow rate and pressure) by diverse characterizations. The external antenna voltage and current increase with the augment of RF power, whereas decline with the enhancement of gas pressure and flow rate conversely.Compared with gas flow rate and pressure, the power transfer efficiency is significantly improved by RF power, and achieved its maximum value of 0.85 after RF power injected excess125 W. Optical emission spectroscopy(OES) provides the local mean values of electron excited temperature and electron density in inductively coupled plasma(ICP) post regime, which vary in a range of 0.81 eV to 1.15 eV and 3.7×10~(16)m~(-3)to 8.7×10~(17)m~(-3)respectively. Numerical results of the average magnitudes of electron temperature and electron density in twodimensional distribution exhibit similar variation trend with the experimental results under different operating condition by using COMSOL Multiphysics. By comprehensively understanding the characteristics in a low pressure ICP, optimized operating conditions could be anticipated aiming at different academic and industrial applications.     

Effect of inductively coupled plasma surface treatment on silica gel and mesoporous MCM-41 particles

Silica gel and MCM-41 synthesized mesoporous materials were treated with either oxygen (O2),hexamethyldisiloxane (HMDSO) and organic vapors like ethanol (EtOH),and acrylonitrile (AN) inductive plasma.The radiofrequency power for the modification was fixed to 120 W and 30 min,assuring a high degree of organic ionization energy in the plasma.The surface properties were studied by infrared spectroscopy (FTIR),scanning electron microscopy,x-ray photoelectron spectroscopy and dynamic light scattering technique was used for characterizing size distributions.When the silica and MCM-41 particles were modified by AN and HMDSO plasma gases,the surface morphology of the particles was changed,presenting another color,size or shape.In contrast,the treatments of oxygen and EtOH did not affect the surface morphology of both particles,but increased the oxygen content at the surface bigger than the AN and HMDSO plasma treatments.In this study,we investigated the influence of different plasma treatments on changes in morphology and the chemical composition of the modified particles which render them a possible new adsorbent for utilization in sorptive extraction techniques for polar compounds.     

应用CFD方法研究雷诺数对烟囱气体混合均匀性影响北大核心CSCD

为研究各种流态下核设施烟囱内气体混合均匀性情况,应用计算流体力学(CFD)方法,建立了仿真模型,主烟囱内雷诺数范围800~70000。仿真结果表明:雷诺数变化对于主烟道风速分布有重要影响;8倍水力直径以下,随监测截面升高,风速分布将更为均匀,8倍水力直径以上,一定程度内增强湍流,可提高风速分布均匀性,流态处于完全湍流后,继续提高雷诺数对风速的分布均匀性无益;对于示踪气体,各监测截面均达到了较充分的混合,管道内雷诺数低于29000时,其在各截面上的混合均匀性伴随雷诺数升高有细微的降低,雷诺数超过29000后混合均匀性变化不再显著。对比仿真结果与试验结果,风速及示踪气体浓度仿真结果与试验测量值具有较好的一致性。     

Numerical study of the flow structures in flat plate and the wall-mounted hump induced by the unsteady DBD plasma

In this work,the dielectric-barrier-discharge plasma actuator was employed to study the flow structures induced by the plasma actuator over a flat plate and a wall-mounted hump.A phenomenological dielectric-barrier-discharge plasma model which regarded the plasma effect as the body force was implemented into the Navier–Stokes equations solved by the method of large eddy simulations.The results show that a series of vortex pairs,which indicated dipole formation and periodicity distribution were generated in the boundary layer when the plasma was applied to the flow over a flat plane.They would enhance the energy exchanged between the near wall region and the free stream.Besides,their spatial trajectories are deeply affected by the actuation strength.When the actuator was engaged in the flow over a wall-mounted hump,the vortex pairs were also produced,which was able to delay flow separation as well as to promote flow reattachment and reduce the generation of a vortex,achieving the goal of reducing dissipation and decreasing flow resistance.     

Experimental and simulated investigation of microdischarge characteristics in a pin-to-pin dielectric barrier discharge (DBD) reactor

Both experimental and simulated studies of microdischarge (MD) are carried out in a dielectric barrier discharge with a pin-to-pin gap of 3.5 mm, ignited by a sinusoidal voltage with a peak voltage of 10 kV and a driving frequency of 5 kHz. Statistical results have shown that the probability of the single current pulse in the positive half-period (HP) reaches 73.6% under these conditions. Experimental results show that great luminous intensity is concentrated on the dielectric surface and the tip of the metal electrode. A 1D plasma fluid model is implemented by coupling the species continuity equations, electron energy density equations, Poisson equation, and Helmholtz equations to analyze the MD dynamics on the microscale. The simulated results are in good qualitative agreement with the experimental results. The simulated results show that the MD dynamics can be divided into three phases: the Townsend phase, the streamer propagation phase, and the discharge decay phase. During the streamer propagation phase, the electric field and electron density increase with the streamer propagation from the anode to the cathode, and their maximal values reach 625.48 Td and 2.31 × 1019 m−3, as well as 790.13 Td and 3.58 × 1019 m−3 in the positive and negative HP, respectively. Furthermore, a transient glow-like discharge is detected around the anode during the same period of streamer propagation. The formation of transient glow-like discharge is attributed to electrons drifting back to the anode, which is driven by the residual voltage in the air gap.     

Co-synthesis of vertical graphene nanosheets and high-value gases using inductively coupled plasma enhanced chemical vapor deposition

One-step controllable synthesis of vertical graphene nanosheets (VGs) and high-value gases was achieved using inductively coupled plasma enhanced chemical vapor deposition (ICPECVD). The basic physical properties of the ICPECVD process were revealed via electrical diagnosis and optical emission spectroscopy. The coil current and voltage increased linearly with the augmenting of injected power, and CH, C₂, H₂ and H were detected at a wavelength from 300 to 700 nm, implying the generation of abundant graphene-building species. The morphology and structure of solid carbon products, graphene nanosheets, were systemically characterized in terms of the variations of operating conditions, such as pressure, temperature, gas proportion, etc. The results indicated that an appropriate operating condition was indispensable for the growth process of graphene nanosheets. In the present work, the optimized result was achieved at the pressure, heating temperature, applied power and gas proportion of 600mTorr, 800 °C, 500 W and 20:20:15, respectively, and the augmenting of both CH₄ and H₂ concentrations had a positive effect on the etching of amorphous carbon. Additionally, H₂ and C₂ hydrocarbons were detected as the main exhaust gases. The selectivity of H₂ and C₂H₂ , measured in exhaust gases, reached up to 52% and 8%, respectively, which implied a process of free radical reactions and electron collision dissociation. Based on a comprehensive investigation of spectral and electrical parameters and synthesized products, the reaction mechanism of collision, dissociation, diffusion, etc, in ICPECVD could be speculated, providing a probable guide for experimental and industrial applications.