Modulation of the plasma uniformity by coil and dielectric window structures in an inductively coupled plasma

The effects of coil and dielectric window structures on the plasma distribution are examined in a cylindrically symmetric planar inductively coupled plasma(ICP). A two-dimensional(2 D) fluid model is employed to investigate the design issues of ICP source for etching. When the gradient coil structure is applied at 400 W and 20 mTorr, the ionization rate caused by the power deposition decreases at the reactor center as compared to that in a reactor with a planar coil above the planar dielectric window, and a rather uniform plasma is obtained. However, for the vertical coil geometry, all the coils move to the position of the outermost coil, and the peaks of the power deposition and ionization rate appear at the radial edge of the substrate. In this case, the plasma density is characterized by an edge-high profile. Further, it is observed that the plasma uniformity is improved by increasing the source power under a gas pressure of 20 mTorr and becomes better when the gas pressure increases to 30 mTorr with the source power being fixed at400 W in the gradient coil configuration, but the uniformity of plasma worsens with the rising source power or pressure due to the strong localization in the vertical coil geometry. Moreover,when the discharge is sustained in a reactor with a stepped dielectric window at r = 0.135 m, the best plasma uniformity is obtained at 400 W and 20 m Torr because the ionization rate is enhanced at the outermost coil, and the dielectric window at r = 0.135 m blocks the diffusion of plasma towards the axis. In addition, higher source power and lower gas pressure produce more uniform plasma for the designs with a stepped window near the symmetry axis. When the dielectric window is stepped at r = 0.135 m, the non-uniformity of plasma initially decreases and then increases with the increase in source power or gas pressure. When the dielectric window is stepped at the radial edge of the chamber, the plasma uniformity is improved by increasing the source power and gas pressure due to the enhanced ionization at the larger radius caused by the severe localization.     

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.     

Numerical simulation and experimental research on an inductively coupled RF plasma cathode

In this study, numerical simulation and discharge current tests were conducted on an inductively coupled radio frequency (RF) plasma cathode. Numerical simulations and experimental measurements were performed to study the factors influencing the electron extraction characteristics, including the gas type, gas flow, input power and extracting voltage. The simulation results were approximately consistent with the experimental results. We experimentally found that the RF input power mainly determines the extracted electron current. An electron current greater than 1 A was acquired at 270 W (RF input power), 2.766 sccm (xenon gas). Our results prove that an inductively coupled RF plasma cathode can be reasonable and feasible, particularly for low power electric propulsion devices.     

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.     

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.     

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.     

Mass spectrometry,with an inductively coupled plasma,of inorganic trace impurities in ultrapure water

Conclusions The final result of investigations of the mass spectrometer with an inductively coupled plasma for analysis of inorganic trace impurities in ultrapure water was the development of instrumental-methodological techniques for increasing the efficiency and reliability of the recording process. This made it possible to choose internal calibration standards and criteria for changing the calibration coefficients. The research instrumentation complex, developed at the All-Union Scientific-Research Institute of Technical and Physical Apparatus, is suitable for quantitative analysis of the elemental content of trace impurities in water with the indicated analytic characteristics for the relative method of measurement according to internal calibration standards. A further improvement of the research apparatus is lower transmission losses which result from the effect of the edge fields according to the constant and variable components, with the aid of a nonuniform standing wave of voltage applied to the mass analyzer as well as the detection limit obtained with the aid of an ion-trap-type detector. The preliminary results show that these techniques make it possible to improve transmission by up to a factor of 30 and to work with a resolution of 100M, as well as to decrease the detection limits by a factor of 10. In conclusion, we thank S. S. Grazhulen and Yu. I. Popandopulo (Institute of Applied and Theoretical Mechanics of the Russian Academy of Sciences) for collaboration and assistance in performing the control measurements of the impurity content in the samples on the VG Elemental PQ2 mass spectrometer with an inductively coupled plasma, S. G. Galaktionov and A. L. Makarov (All Union Scientific-Research Institute of Chemical Technology) for providing the samples, and A. A. Sysoev (Moscow Engineering Institute) for a helpful discussion of the results. All-Union Scientific-Research Institute of Technical and Physical Apparatus. Translated from Atomnaya énergiya, Vol. 77, No. 2, pp. 134–140, August, 1994.     

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。     

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.     

用INAA法和ICP-MS法对蚯蚓样品作多元素测定比较

用仪器中子活化分析方法对６例蚯蚓样品进行了Ａｓ、Ｂａ、Ｃｄ、Ｃｏ、Ｃｒ、Ｃｕ、Ｆｅ、Ｍｎ、Ｈｇ、Ｒｂ、Ｓｂ、Ｓｅ和Ｚｎ的元素含量测定,并用等离子质谱分析方法和人发标准参考物质进行了比较和核对。结果表明,两种测定方法分析结果相符,大多数元素的相对偏差在±２０％以内。     

On the potential of tungsten-vanadium composites for high temperature application with wide-range thermal operation window

The present study is concerned with the numerical design of a composite material consisting of tungsten and vanadium for application in future nuclear fusion plants. The proposed composite material combines a significant creep resistance at high temperatures with a reasonable fracture toughness in the low temperature range and, compared to its constituents, features an enhanced thermal operation window. In a first step, a numerical screening analysis is performed for a comparison of different types of composite materials including particle, short fiber and infinite fiber reinforced composites with both, regular and random microstructures. The different options are compared with respect to their thermal and mechanical properties as well as their creep resistance. In a preliminary experimental investigation, a first trial heat of the composite is processed and tested for its creep resistance at 1000 °C and its fracture toughness at ambient temperature. The results reveal a distinct potential of the material.     

电感耦合等离子体质谱法测定水中钍

用Mg(OH)₂对水中钍进行浓集后,采用电感耦合等离子体质谱法(ICP-MS)对其进行测量。结果表明,方法线性相关系数为0.999 6,加标回收率在82.5%～92.2%之间,平行样的相对标准偏差约5%,方法的测定下限为1.2 ng/L。采用本方法对2015年第3季度湖北省国控点和省控点样品进行分析,19个样品的测量值范围为7~149 ng/L,在历年测量值范围之内。     

Investigation of operating parameters on CO2 splitting by dielectric barrier discharge plasma

Experiments of CO2 splitting by dielectric barrier discharge (DBD) plasma were carried out,and the influence of CO2 flow rate,plasma power,discharge voltage,discharge frequency on CO2 conversion and process energy efficiency were investigated.It was shown that the absolute quantity of CO2 decomposed was only proportional to the amount of conductive electrons across the discharge gap,and the electron amount was proportional to the discharge power;the energy efficiency of CO2 conversion was almost a constant at a lower level,which was limited by CO2 inherent discharge character that determined a constant gap electric field strength.This was the main reason why CO2 conversion rate decreased as the CO2 flow rate increase and process energy efficiency was decreased a little as applied frequency increased.Therefore,one can improve the CO2 conversion by less feed flow rate or larger discharge power in DBD plasma,but the energy efficiency is difficult to improve.     

Numerical investigation on the effect of gas parameters on ozone generation in pulsed dielectric barrier discharge

Pulsed dielectric barrier discharge is a promising technology for ozone generation and is drawing increasing interest. To overcome the drawback of experimental investigation, a kinetic model is applied to numerically investigate the effect of gas parameters including inlet gas temperature, gas pressure, and gas flow rate on ozone generation using pulsed dielectric barrier discharge. The results show that ozone concentration and ozone yield increase with decreasing inlet gas temperature, gas pressure, and gas flow rate. The highest ozone concentration and ozone yield in oxygen are about 1.8 and 2.5 times higher than those in air, respectively. A very interesting phenomenon is observed: the peak ozone yield occurs at a lower ozone concentration when the inlet gas temperature and gas pressure are higher because of the increasing average gas temperature in the discharge gap as well as the decreasing reduced electric field and electron density in the microdischarge channel. Furthermore, the sensitivity and rate of production analysis based on the specific input energy (SIE) for the four most important species O₃, O, O(1D), and O₂(b¹∑) are executed to quantitatively understand the effects of every reaction on them, and to determine the contribution of individual reactions to their net production or destruction rates. A reasonable increase in SIE is beneficial to ozone generation. However, excessively high SIE is not favorable for ozone production.     

Comparison of two models for a high temperature reactor coupled to a gas turbine

This paper presents two independent dynamic models of a nuclear gas turbine power plant. Both the high temperature nuclear reactor (HTR) and its energy conversion system (ECS) based on a direct Brayton cycle have been modelled. One model utilises RELAP5 for the ECS, the other Aspen Custom Modeler (ACM). The reactor model used in both models is a point kinetic model derived from a detailed reactor model. The ECS model is described and compared componentwise, with an emphasis on the turbomachinery. The total plant models are compared with each other by calculating two representative transients: one load rejection transient and one transient with the system at part load.     

Particle-in-cell simulation for effect of anode temperature on discharge characteristics of a Hall effect thruster

Propellant gas flow has an important impact on the ionization and acceleration process of Hall effect thrusters (HETs). In this paper, a particle-in-cell numerical method is used to study the effect of the anode temperature, i.e., the flow speed of the propellant gas, on the discharge characteristics of a HET. The simulation results show that, no matter the magnitude of the discharge voltage, the calculated variation trends of performance parameters with the anode temperature are in good agreement with the experimental ones presented in the literature. Further mechanism analysis indicates that the magnitude of the electron temperature is responsible for the two opposing variation laws found under different discharge voltages. When the discharge voltage is low, the electron temperature is low, and so is the intensity of the propellant ionization; the variation of the thruster performance with the anode temperature is thereby determined by the variation of the neutral density that affects the propellant utilization efficiency. When the discharge voltage is high, the electron temperature is large enough to guarantee a high degree of the propellant utilization no matter the magnitude of the anode temperature. The change of the thruster performance with the anode temperature is thus dominated by the change of the electron temperature and consequently the electron-neutral collisions as well as the electron cross-field mobility that affect the current utilization efficiency.     

Isotope dilution inductively coupled plasma mass spectrometry for determination of 126Sn content in spent nuclear fuel sample

The ¹²⁶Sn content in a spent nuclear fuel solution was determined by isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) for its inventory estimation in high-level radioactive waste. A well-characterized irradiated UO₂ fuel sample dissolved in a hot cell was used as a sample to evaluate the reliability of the methodology. Prior to the ICP-MS measurement, Sn was separated from Te (¹²⁶Te), which causes major isobaric interference in the determination of ¹²⁶Sn content, along with highly radioactive coexisting elements, such as Sr (⁹⁰Sr), Y (⁹⁰Y), Cs (¹³⁷Cs) and Ba (^137m Ba), using an anion-exchange column. The absence of counts attributed to Te at m/z = 125, 128, and 130 in the Sn-containing effluent (Sn fraction) indicates that Te was completely removed from the anion-exchange column. After washing, Sn retained on the column was readily eluted with 1 M HNO₃ accompanied with approximately 80% of the Cd and 0.03% of the U in the initial sample. Owing to the presences of Cd and U in Sn fraction, the measurements of ¹¹⁶Sn and ¹¹⁹Sn were affected by the isobaric ¹¹⁶Cd and the doubly charged ²³⁸U²⁺ion, resulting in the positive bias of the determined values. With the exception of the isotopic ratios including ¹¹⁶Sn and ¹¹⁹Sn, ¹¹⁷Sn/¹²⁶Sn, ¹¹⁸Sn/¹²⁶Sn, ¹²⁰Sn/¹²⁶Sn, ¹²²Sn/¹²⁶Sn and ¹²⁴Sn/¹²⁶Sn were successfully determined and showed good agreement with those obtained through ORIGEN2 calculations. The measured concentration of ¹²⁶Sn in the spent nuclear fuel sample solution was 0.74 ± 0.14 ng/g, which corresponds to 23.0 ± 4.5 ng per gram of the irradiated UO₂ fuel (excluding the presence of ¹²⁶Sn in the insoluble residue). The results reported in this paper are the first experimental values of ¹²⁶Sn content and isotope ratios in the spent nuclear fuel solution originating in spent nuclear fuel irradiated at a nuclear power plant in Japan.     

Evaluation of a detailed radiation heat transfer model in a high temperature reactor systems simulation model

Radiation heat transfer is a major mode of heat transfer in high temperature gas-cooled reactors (HTRs) because of the high operating temperatures. It is, however, a difficult phenomenon to calculate in full detail due to its geometrical complexity. One has to use either a numerical method or complex analytical view factor formulae. Except the difficulty of view factor calculation, a vast number of calculation elements are required to consider all interacting surfaces around a cavity. A common approximation in systems simulation codes is to connect only directly opposing surfaces with a view factor of one.The accuracy of this approximation was investigated with a finite volume, two-dimensional axial-symmetric reactor model implemented in the systems simulation code Flownex. A detailed radiation model was developed and also implemented in the Flownex reactor model. This paper also describes the analytical formulae for view factor calculation in this detailed radiation heat transfer model.The HTR-10 and the 268 MW version of the PBMR were used as case studies in which Loss-of-Flow events without SCRAM were simulated. In these simulations, the time to reach recriticality was used as an indicator of heat removal effectiveness.With the HTR-10, other non-linear phenomena in the reactor core constrained the solution process, so that the number of radiation elements had no effect on solution time, while with the 268 MW PBMR DLOFC, the use of a detailed radiation model increased solution time with 30%.With both the HTR-10 and the PBMR, the radiation model had negligible effect on the total heat resistance from the reactor, as indicated by the time elapsed until recriticality.For system simulation codes that focus on transient response of a plant, it is not considered worthwhile to use a detailed radiation model, as the gain in accuracy does not justify the increased solution time or the implementation and verification effort.