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Experimental studies of H_(2)/Ar plasma in a cylindrical inductive discharge with an expansion region

Chinese Physics B 2024年第10期33卷 321-330页

作者： Shi-Bo Li Si-Yu Xing Fei Gao you-nian wang Key Laboratory of Materials Modification by Laser Ionand Electron Beams(Ministry of Education)School of PhysicsDalian University of TechnologyDalian 116024China

The electrical parameters of H_(2)/Ar plasma in a cylindrical inductive discharge with an expansion region are investigated by a Langmuir probe,where Ar fractions range from 0%to 100%.The influence of gas composition and pressure on electron density,the effective electron temperature and the electron energy probability functions(EEPFs)at different spatial positions are *** driver region,with the introduction of a small amount of Ar at 0.3 Pa,there is a rapid increase in electron density accompanied by a decrease in the effective electron ***,the shape of the EEPF transitions from a three-temperature distribution to a bi-Maxwellian distribution due to an increase in electron-electron ***,this phenomenon resulting from the changes in gas composition vanishes at 5 Pa due to the prior depletion of energetic electrons caused by the increase in pressure during hydrogen *** EEPFs for the total energy in expansion region is coincident to these in the driver region at 0.3 Pa,as do the patterns of electron density variation between these two regions for differing Ar *** 5 Pa,as the discharge transitions from H_(2)to Ar,the EEPFs evolved from a bi-Maxwellian distribution with pronounced low energy electrons to a Maxwellian distribution in expansion *** evolve may be attributed to a reduction in molecular vibrational excitation reactions of electrons during transport and the transition from localized electron dynamics in hydrogen discharge to non-localized electron dynamics in argon *** order to validate the experimental results,we use the COMSOL simulation software to calculate electrical parameters under the same *** evolution and spatial distribution of the electrical parameters of the simulation results agree well with the trend of the experimental results.

关键词： inductively coupled plasma transmission and distribution energy distribution functions

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Power transfer efficiency in an air-breathing radio frequency ion thruster

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Chinese Physics B 2024年第7期33卷 430-438页

作者：黄高煌李宏高飞王友年 Key Laboratory of Materials Modification by Laser Ionand Electron Beams(Ministry of Education)School of PhysicsDalian University of TechnologyDalian 116024China College of Physical Science and Technology Dalian UniversityDalian 116622China

Due to a series of challenges such as low-orbit maintenance of satellites, the air-breathing electric propulsion has got widespread attention. Commonly, the radio frequency ion thruster is favored by low-orbit missions due to its high specific impulse and efficiency. In this paper, the power transfer efficiency of the radio frequency ion thruster with different gas compositions is studied experimentally, which is obtained by measuring the radio frequency power and current of the antenna coil with and without discharge operation. The results show that increasing the turns of antenna coils can effectively improve the radio frequency power transfer efficiency, which is due to the improvement of Q factor. In pure N_2 discharge,with the increase of radio frequency power, the radio frequency power transfer efficiency first rises rapidly and then exhibits a less steep increasing trend. The radio frequency power transfer efficiency increases with the increase of gas pressure at relatively high power, while declines rapidly at relatively low power. In N_(2)/O_(2) discharge, increasing the N_(2) content at high power can improve the radio frequency power transfer efficiency, but the opposite was observed at low power. In order to give a better understanding of these trends, an analytic solution in limit cases is utilized, and a Langmuir probe was employed to measure the electron density. It is found that the evolution of radio frequency power transfer efficiency can be well explained by the variation of plasma resistance, which is related to the electron density and the effective electron collision frequency.

关键词： radio frequency ion thruster inductively coupled plasma power transfer efficiency analytic solution

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Current neutralization and plasma polarization for intense ion beams propagating through magnetized background plasmas in a two-dimensional slab approximation

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Frontiers of physics 2014年第2期9卷 226-233页

作者： Zhang-Hu Hu Mao-Du Chen you-nian wang School of Physics and Optoeleetronic Technology Dalian University of Technology Dalian 116024 China

A two-dimensional electromagnetic Particle-in-Cell （PIC） simulation model is proposed to study the propagation of intense, ion beams with beaIn width wb small compared to the electron skin depth c/wpe through background plaslnas in tile presence of external applied magnetic fields. The effcctive eleetron gyrora,dius wge is found to be an important parameter for ion beam transport in the presence of magnetic fields,In the bealn regions, the background plasmas respond differently to the ion beanl of width wb〈wge and wb 〉 wge for the given magnetic field and beaan encrgy, For the case of beam width wb 〈 wge with relative weak external magnetic fiehts, the rotalion effects of plasma electrons a,re found to be signifieant and contributes to the signitica,nt enilaneeinent of the self electric and seif-magnetic fields. While for the ease of beam width wb 〉 wge with relative strong external magnetic fields, the rotation effects of plasma cleetrons are strongly inhibited and a, well neutraliza, tion of ion beam current can be found. Finally, the influences of diftiuent beam widths. beam energies and magnetic fields on the neutralization of ion bc, anl eurrellt are summarized for the eases of wb 〈 wge〈 c/wpe,wge 〈wb〈c/wbp and wb〈c/wpe〈wge.

关键词： current neutralization ion beams magnetized plasmas Particle-in-Cell simulations

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Spatio-temporal measurements of overshoot phenomenon in pulsed inductively coupled discharge

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Chinese Physics B 2021年第4期30卷 369-375页

作者： Xiang-Yun Lv Fei Gao Quan-Zhi Zhang you-nian wang Key Laboratory of Materials Modification by Laser Ionand Electron Beams(Ministry of Education)School of PhysicsDalian University of TechnologyDalian 116024China

Pulse inductively coupled plasma has been widely used in the microelectronics industry,but the existence of overshoot phenomenon may affect the uniformity of plasma and generate high-energy ions,which could damage the *** overshoot phenomenon at various spatial locations in pulsed inductively coupled Ar and Ar/CF_(4) discharges is studied in this *** electron density,effective electron temperature,relative light intensity,and electron energy probability function(EEPF) are measured by using a time-resolved Langmuir probe and an optical probe,as a function of axial and radial *** the initial stage of pulse,both electron density and relative light intensity exhibit overshoot phenomenon,i.e.,they first increase to a peak value and then decrease to a convergent *** overshoot phenomenon gradually decays,when the probe moves away from the ***,a delay appears in the variation of the electron densities,and the effective electron temperature decreases,which may be related to the reduced strength of electric field at a distance,and the consequent fewer high-energy electrons,inducing limited ionization and excitation *** overshoot phenomenon gradually disappears and the electron density decreases,when the probe moves away from reactor *** Ar/CF_(4) discharge,the overshoot phenomenon of electron density is weaker than that in the Ar discharge,and the plasma reaches a steady density within a much shorter time,which is probably due to the more ionization channels and lower ionization thresholds in the Ar/CF_(4) plasma.

关键词： pulse inductively coupled plasma overshoot spatial distribution

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Phase shift effects of radio-frequency bias on ion energy distribution in continuous wave and pulse modulated inductively coupled plasmas

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Chinese Physics B 2018年第4期27卷 346-351页

作者： Chan Xue Fei Gao Yong-Xin Liu Jia Liu you-nian wang Key Laboratory of Materials Modification by Laser Ion and Electron Beams (Ministry of Education) School of Physics Dalian University of Technology Dalian 116024 China Shanghai Institute of Space Propulsion Shanghai 201112 China

A retarding field energy analyzer（RFEA） is used to measure the time-averaged ion energy distributions（IEDs） on the substrate in both continuous wave（CW） and synchronous pulse modulated radio-frequency（RF） inductively coupled Ar plasmas（ICPs）.The effects of the phase shift θ between the RF bias voltage and the RF source on the IED is investigated under various discharge *** is found that as θ increases from 0 to π,the IED moves towards the low-energy side,and its energy width becomes *** order to figure out the physical mechanism,the voltage waveforms on the substrate are also *** results show that as θ increases from 0 to π,the amplitude of the voltage waveform decreases and,meanwhile,the average sheath potential decreases as ***,the potential drop in the sheath on the substrate exhibits a maximum value at the same phase（i.e.,θ = 0） and a minimum value at the opposite phase（i.e.,θ = π）.Therefore,when ions traverse across the sheath region above the substrate,they obtain less energies at lower sheath potential drop,leading to lower ion ***,as θ increases from π to 2π,the IEDs and their energy widths change reversely.

关键词： ion energy distribution phase shift synchronous pulse modulated inductively coupled plasmas

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Measurement of electronegativity during the E to H mode transition in a radio frequency inductively coupled Ar/O2 plasma

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Chinese Physics B 2021年第3期30卷 371-377页

作者： Peng-Cheng Du Fei Gao Xiao-Kun wang Yong-Xin Liu you-nian wang Key Laboratory of Materials Modification by Laser Ionand Electron Beams(Ministry of Education)School of PhysicsDalian University of TechnologyDalian 116024China

This paper presents the evolution of the electronegativity with the applied power during the E to H mode transition in a radio frequency(rf)inductively coupled plasma(ICP)in a mixture of Ar and *** densities of the negative ion and the electron,as well as their ratio,i.e.,the electronegativity,are measured as a function of the applied power by laser photo-detachment combined with a microwave resonance probe,under different pressures and O2 ***,the optical emission intensities at Ar 750.4 nm and O 844.6 nm are monitored via a *** was found that by increasing the applied power,the electron density and the optical emission intensity show a similar trench,i.e.,they increase abruptly at a threshold power,suggesting that the E to H mode transition *** the increase of the pressure,the negative ion density presents opposite trends in the E-mode and the H-mode,which is related to the difference of the electron density and energy for the two *** emission intensities of Ar 750.4 nm and O 844.6 nm monotonously decrease with increasing the pressure or the O2 content,indicating that the density of high-energy electrons,which can excite atoms,is monotonically *** leads to an increase of the negative ion density in the H-mode with increasing the ***,as the applied power is increased,the electronegativity shows an abrupt drop during the E-to H-mode transition.

关键词： electronegativity E to H mode transition radio frequency inductively coupled plasma

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Fluid simulation of the pulsed bias effect on inductively coupled nitrogen discharges for low-voltage plasma immersion ion implantation

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Chinese Physics B 2017年第1期26卷 290-297页

作者： Xiao-Yan Sun Yu-Ru Zhang Xue-Chun Li you-nian wang Key Laboratory of Materials Modification by Laser Ion and Electron Beams （Ministry of Education） School of Physics and Optoelectronic Technology Dalian University of Technology Dalian 116024 China

Planar radio frequency inductively coupled plasmas（ICP） are employed for low-voltage ion implantation processes,with capacitive pulse biasing of the substrate for modulation of the ion energy. In this work, a two-dimensional（2D） selfconsistent fluid model has been employed to investigate the influence of the pulsed bias power on the nitrogen plasmas for various bias voltages and pulse frequencies. The results indicate that the plasma density as well as the inductive power density increase significantly when the bias voltage varies from 0 V to-4000 V, due to the heating of the capacitive field caused by the bias power. The N＋fraction increases rapidly to a maximum at the beginning of the power-on time, and then it decreases and reaches the steady state at the end of the glow period. Moreover, it increases with the bias voltage during the power-on time, whereas the N2-＋ fraction exhibits a reverse behavior. When the pulse frequency increases to 25 kHz and40 kHz, the plasma steady state cannot be obtained, and a rapid decrease of the ion density at the substrate surface at the beginning of the glow period is observed.

关键词： fluid simulation low-voltage plasma immersion ion implantation N2 inductive discharge

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Numerical investigation of radio-frequency negative hydrogen ion sources by a three-dimensional fluid model

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Chinese Physics B 2021年第9期30卷 335-345页

作者： Ying-Jie wang Jia-Wei Huang Quan-Zhi Zhang Yu-Ru Zhang Fei Gao you-nian wang Key Laboratory of Materials Modification by Laser Ionand Electron Beams(Ministry of Education)School of PhysicsDalian University of TechnologyDalian 116024China

A three-dimensional fluid model is developed to investigate the radio-frequency inductively coupled H2 plasma in a reactor with a rectangular expansion chamber and a cylindrical driver chamber,for neutral beam injection system in *** this model,the electron effective collision frequency and the ion mobility at high E-fields are employed,for accurate simulation of discharges at low pressures(0.3 Pa-2 Pa)and high powers(40 kW-100 kW).The results indicate that when the high E-field ion mobility is taken into account,the electron density is about four times higher than the value in the low E-field *** addition,the influences of the magnetic field,pressure and power on the electron density and electron temperature are *** is found that the electron density and electron temperature in the xz-plane along permanent magnet side become much more asymmetric when magnetic field ***,the plasma parameters in the yz-plane without permanent magnet side are symmetric no matter the magnetic field is applied or ***,the maximum of the electron density first increases and then decreases with magnetic field,while the electron temperature at the bottom of the expansion region first decreases and then almost keeps *** the pressure increases from 0.3 Pa to 2 Pa,the electron density becomes higher,with the maximum moving upwards to the driver region,and the symmetry of the electron temperature in the xz-plane becomes much *** power increases,the electron density rises,whereas the spatial distribution is *** can be summarized that the magnetic field and gas pressure have great influence on the symmetry of the plasma parameters,while the power only has little effect.

关键词： negative hydrogen ion source inductively coupled plasma three-dimensional fluid model magnetic field effect

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Time-resolved radial uniformity of pulse-modulated inductively coupled O_(2)/Ar plasmas

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Chinese Physics B 2021年第6期30卷 401-408页

作者： Wei Liu Chan Xue Fei Gao Yong-Xin Liu you-nian wang Yong-Tao Zhao School of Optoelectronic Engineering Xi'an Technological UniversityXi'an 710021China School of Science Xi'an Jiaotong UniversityXi'an 710049China School of Aerospace Science and Technology Xidian UniversityXi'an 710126China School of Physics Dalian University of TechnologyDalian 116024China

Time-resolved radial uniformity of pulse-modulated inductively coupled O_(2)/Ar plasma has been investigated by means of a Langmuir probe as well as an optical probe in this paper. The radial uniformity of plasma has been discussed through analyzing the nonuniformity factor β(calculated by the measured n_e, lower β means higher plasma radial uniformity). The results show that during the active-glow period, the radial distribution of ne exhibits an almost flat profile at the beginning phase, but it converts into a parabola-like profile during the steady state. The consequent evolution for β is that when the power is turned on, it declines to a minimum at first, and then it increases to a maximum, after that, it decays until it keeps constant. This phenomenon can be explained by the fact that the ionization gradually becomes stronger at the plasma center and meanwhile the rebuilt electric field(plasma potential and ambipolar potential) will confine the electrons at the plasma center as well. Besides, the mean electron energy( _(on)) at the pulse beginning decreases with the increasing duty cycle. This will postpone the plasma ignition after the power is turned on. This phenomenon has been verified by the emission intensity of Ar(λ = 750.4 nm). During the after-glow period, it is interesting to find that the electrons have a large depletion rate at the plasma center. Consequently, ne forms a hollow distribution in the radial direction at the late stage of after-glow. Therefore, β exhibits a maximum at the same time. This can be attributed to the formation of negative oxygen ion(O^(-)) at the plasma center when the power has been turned off.

关键词： plasma radial uniformity pulse-modulated discharge inductively coupled plasma Langmuir probe

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Shedding light on the reversible deactivation of carbon-supported single-atom catalysts in hydrogenation reaction

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Nano Research 2024年第6期17卷 4807-4814页

作者： Runze Chen Xiaoying wang Jianfei Dang Songjie Yun Liqiang wang Fangong Kong you-nian Liu State Key Laboratory of Biobased Material and Green Papermaking Qilu University of TechnologyJinan 250353China School of Material Science and Engineering Zhengzhou UniversityZhengzhou 450001China School of Chemical Engineering Zhengzhou UniversityZhengzhou 450001China Hunan Provincial Key Laboratory of Micro&Nano Materials Interface Science College of Chemistry and Chemical EngineeringCentral South UniversityChangsha 410083China

Carbon-supported single-atom catalysts were found to suffer reversible deactivation in catalytic hydrogenation,but the mechanism is still ***,nitro compounds hydrogenation catalyzed by N-doped carbon-supported Co single atom(Co1/NC)was taken as a model to uncover the mechanism of the reversible deactivation ***1/NC exhibited moderate adsorption towards the substrate molecules(i.e.,nitro compounds or related intermediates),which could be strengthened by the confinement effect from the porous ***,substrate molecules tend to accumulate within the pore channel,especially micropores that host Co1,making it difficult for the reactants to access the active sites and finally leading to their *** situation could be even worse when the substrate molecules possess a large ***,the catalytic activity of Co1/NC could be restored via a simple thermal treatment,which could remove the adsorbates within the pore channel,hence releasing active sites that were originally inaccessible to reactants.

关键词： single-atom catalysts porous carbon support reversible deactivation mechanistic study hydrogenation reaction

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