共查询到20条相似文献，搜索用时 15 毫秒
1.
Mingyang WU Chijie XIAO Yue LIU Xiaoyi YANG Xiaogang WANG Chang TAN Qi SUN 《等离子体科学和技术》2021,23(8):85002-37
In this study, a code, named Peking University Helicon Discharge(PHD), which can simulate helicon discharge processes under both a background magnetic field greater than 500 G and a pressure less than 1 Pa, is developed. In the code, two fluid equations are used. The PHD simulations led to two important findings:(1) the temporal evolution of plasma density with the background magnetic field exhibits a second rapid increase(termed as the second density jump),similar to the transition of modes in helicon plasmas;(2) in the presence of a magnetic field, the peak positions of electron power absorption appeared near the central axis, unlike in the case of no magnetic field. These results may lead to an enhanced understanding of the discharge mechanism. 相似文献
2.
Yueqing WANG 《等离子体科学和技术》2022,24(3):35401
We present in this paper the comparison of an electric double layer (DL) in argon helicon plasma and magnetized direct current (DC) discharge plasma. DL in high-density argon helicon plasma of 13.56 MHz RF discharge was investigated experimentally by a floating electrostatic probe and local optical emission spectroscopy (LOES). The DL characteristics at different operating parameters, including RF power (300–1500 W), tube diameter (8–60 mm), and external magnetic field (0–300 G), were measured. For comparison, DL in magnetized plasma channel of a DC discharge under different conditions was also measured experimentally. The results show that in both cases, DL appears in a divergent magnetic field where the magnetic field gradient is the largest and when the plasma density is sufficiently high. DL strength (or potential drop of DL) increases with the magnetic field in two different structures. It is suggested that the electric DL should be a common phenomenon in dense plasma under a gradient external magnetic field. DL in magnetized plasmas can be controlled properly by magnetic field structure and discharge mode (hence the plasma density). 相似文献
3.
A new type of hybrid discharge is experimentally investigated in this work. A helicon source and an electron cyclotron resonance(ECR) source were combined to produce plasma. As a preliminary study of this type of plasma, the optical emission spectroscopy(OES) method was used to obtain values of electron temperature and density under a series of typical conditions. Generally,it was observed that the electron temperature decreases and the electron density increases as the pressure increased. When increasing the applied power at a certain pressure, the average electron density at certain positions in the discharge does not increase significantly possibly due to the high degree of neutral depletion. Electron temperature increased with power in the hybrid mode.Possible mechanisms of these preliminary observations are discussed. 相似文献
4.
胡鹏;张文瀚;孙建冬;鹿畅;陈冲;韩亚杰;韩道满;刘旭辉;孙斌 《等离子体科学和技术》2025,27(6):064011-1-064011-9
A new magnetic field configuration is proposed by introducing a cusped field to the helicon plasma thruster (HPT), and the effects of the cusped field on the discharge characteristics of the HPT are investigated. The experimental results show that the thruster can still achieve a stable W mode discharge with the additional cusped field, while the discharge conditions have been changed so that a higher RF power is required to achieve the W mode under the same experimental conditions. However, the ion density in the plume region is increased by at least one order of magnitude and the ion flux density is increased by a factor of 4 to 5. The ionization enhancement is attributed to the change in magnetic field configuration, which improves the energy coupling efficiency and the ability to confine charged particles (particularly electrons). This magnetic confinement could employ more electrons to ionize the working medium atoms, and the ionization rate is enhanced. The increase in ion density leads to a reduction in the energy available for ion acceleration, resulting in a slight decrease in ion energy. 相似文献
5.
A 1D radially self-consistent model in helicon plasmas has been established to investigate the influence of radial heat conduction on plasma transport and wave propagation. Two kinds of 1D radial fluid models, with and without considering heat conduction, have been developed to couple the 1D plasma–wave interaction model, and self-consistent solutions have been obtained. It is concluded that in the low magnetic field range the radial heat conduction plays a moderate role in the transport of helicon plasmas and the importance depends on the application of the helicon source. It influences the local energy balance leading to enhancement of the electron temperature in the bulk region and a decrease in plasma density. The power deposition in the plasma is mainly balanced by collisional processes and axial diffusion, whereas it is compensated by heat conduction in the bulk region and consumed near the boundary. The role of radial heat conduction in the large magnetic field regime becomes negligible and the two fluid models show consistency. The local power balance, especially near the wall, is improved when conductive heat is taken into account. 相似文献
6.
Yan YANG 《等离子体科学和技术》2022,24(6):65503
A reactive helicon wave plasma (HWP) sputtering method is used for the deposition of tungsten nitride (WNx) thin films. N2 is introduced downstream in the diffusion chamber. The impacts of N2 on the Ar-HWP parameters, such as ion energy distribution functions (IEDFs), electron energy probability functions (EEPFs), electron temperature (Te) and density (ne), are investigated. With the addition of N2, a decrease in electron density is observed due to the dissociative recombination of electrons with ${{rm{N}}}_{2}^{+}.$ The similar IEDF curves of Ar+ and N2+ indicate that the majority of ${{rm{N}}}_{2}^{+}$ stems from the charge transfer in the collision between Ar+ and N2. Moreover, due to the collisions between electrons and N2 ions, EEPFs show a relatively lower Te with a depletion in the high-energy tail. With increasing negative bias from 50 to 200 V, a phase transition from hexagonal WN to fcc-WN0.5 is observed, together with an increase in the deposition rate and roughness 相似文献
7.
The efficiency of radio-frequency (RF) power absorption, RF magnetic field structure andplasma parameters were measured in cylindrical inductive RF plasma sources 20 cm in diameterand 22, 32, 53 cm in length with a low value external magnetic field. The experiments werecarried out in argon at pressures of 13–140 mPa. The RF power supply changed from 200 W to800 W. The spiral antenna was used for sustaining the discharge. It was shown that efficiency ofRF power absorption depended nonlinearly on the external magnetic field values. At maximalvalues of the RF power absorption efficiency, the axial distributions of longitudinal Bz andazimuthalBcomponents of RF magnetic field manifested the formation of the partially standingwave with a half wavelength close to 8 cm. At the same conditions, the axial dependence of theradial RF magnetic field component Br differed drastically. It was concluded that the Bz and Bamplitudes were largely determined by the RF field of Trivelpiece-Gould wave, while Br amplitude represented the radial RF field of the helicon wave. 相似文献
8.
Zhenyu YANG 《等离子体科学和技术》2022,24(7):74006
The helicon plasma source, which generates high thrust and high impulse, is of vital importance for magnetoplasma rocket engines. In this work, a multi-component, two-dimensional, axisymmetric fluid model coupled with an electromagnetic field was developed to model the helicon discharge. The simulation results demonstrate that: (i) the discharge mode changes twice—each conversion is accompanied by a plasma density jump and an electron temperature peak in the discharge; (ii) when the input current increases, the plasma density increases, and ionization occurs faster; (iii) the background magnetic field clearly enhances the discharge; (iv) the plasma density may be smaller if the discharge has not entered the wave mode. 相似文献
9.
Zhikang LU 《等离子体科学和技术》2022,24(9):95403
A helicon wave plasma source in a tube of ring permanent magnets (PMs) has been constructed to study the effect of the configuration of the magnetic field with zero magnetic points on plasma parameters. This device also serves as an exploration platform for a simple, compact helicon wave plasma source adaptable to engineering applications. A small-diameter (26 mm) high-density (∼1018 m−3) blue core plasma is produced in ∼1 Pa argon by helicon RF (radio-frequency) discharge using a Nagoya III antenna under magnetic field (∼2 kG) of compact ring PMs (length ∼204 mm). Operational parameters, i.e. RF power and neutral gas pressure are scanned and plasma density is measured by an RF compensated probe to explore the operating characteristics of the device. Iconic feature of a helicon discharge, such as blue core plasmas and E-H-W mode transitions are well observed in the device, despite the wavelength calculated using the conventional dispersion relation of a bounded whistler waves (Chen 1991 Plasma Phys. Control. Fusion 33 339) is order of magnitudes longer than the length of the plasma in this device which seems to suggest that such helicon device is impossible. Surprisingly, the wavelength calculated by the unbounded whistle wave dispersion formula in turn suggests the occurrence of a half wavelength resonance. 相似文献
10.
孙萌;徐晓芳;王陈文;尹贤轶;陈强;张海宝 《等离子体科学和技术》2024,26(6):064006-1-064006-10
The characteristics of the blue core phenomenon observed in a divergent magnetic field helicon plasma are investigated using two different helical antennas, namely right-handed and left-handed helical antennas. The mode transition, discharge image, spatial profiles of plasma density and electron temperature are diagnosed using a Langmuir probe, a Nikon D90 camera, an intensified charge-coupled device camera and an optical emission spectrometer, respectively. The results demonstrated that the blue core phenomenon appeared in the upstream region of the discharge tube at a fixed magnetic field under both helical antennas. However, it is more likely to appear in a right-handed helical antenna, in which the plasma density and ionization rate of the helicon plasma are higher. The spatial profiles of the plasma density and electron temperature are also different in both axial and radial directions for these two kinds of helical antenna. The wavelength calculated based on the dispersion relation of the bounded whistler wave is consistent with the order of magnitude of plasma length. It is proved that the helicon plasma is part of the wave mode discharge mechanism. 相似文献
11.
In the present work, we report development of a DC glow discharge plasma(GDP) set-up to study controlled evolution of anodic structures having distinctive geometry, size and layers,generated in front of a positively biased electrode, submerged in unmagnetized plasma. For such an anodic structure, we have also investigated the condition under which the turbulence is triggered. Characteristic of these structures, generated in front of a positively biased electrode,depends on multiple parameters such as the ratio of anode to cathode size, electrode separation,gas pressure, biasing configuration such as anode bias, cathode bias and grounding schemes. We attempted to classify different anodic structures observed experimentally, as anode glow, fireball,anode spot, double layer and multiple double layers(MDLs) based on its physical characteristics.Among these structures the present investigation is focused on MDLs. The number of layers,observed in MDLs varied from as high as six to as low as zero, by controlling the operating discharge parameters, externally. Diagnostics were carried out using Langmuir probe. The analysis of floating potential fluctuations corresponds to a multiple anodic structure showed emergence of turbulence, at its critical stage, satisfying condition for self-organized criticality(SOC). This was identified with three slopes observed in the power spectrum, resembling the sand-pile model. Though, the GDP is completely different from that of the magnetically confined plasma, the nature of turbulence observed with SOC, is very similar to that observed in the scrape of layer of fusion devices. Therefore, the present investigation could provide new approach to study turbulence of similar nature, under an experimental condition that is free from the complexities of complicated field geometries used in confinement devices. 相似文献
12.
Modification of exposure conditions downstream in the diffusion chamber has been performed in helicon antenna-excited helium plasma by adjusting the magnetic field(intensity and geometry).In the inductively coupled mode(H mode), a reduction in ion and heat fluxes is found with increasing magnetic field intensity, which is further explained by the more highly magnetized ions off-axis around the last magnetic field lines(LMFL). However, in helicon wave mode(W mode), the increase in magnetic field intensity can dramatically increase the ion and heat fluxes.Moreover, the effect of LMFL geometry on exposure conditions is investigated. In H mode with contracting LMFL, off-axis peaks of both plasma density and electron temperature profiles shift radially inwards, bringing about a beam with better radial uniformity and higher ion and heat fluxes. In W mode, although higher ion and heat fluxes can be achieved with suppressed plasma cross-field diffusion under converging LMFL, the poor radial uniformity and a small beam diameter will limit the size of samples suitable for plasma irradiation experiments. 相似文献
13.
Lü Junxia 《等离子体科学和技术》2005,7(4):2947-2949
This paper discusses a study in which Ti surface alloying has been performed on copper substrates by means of a double glow discharge plasma surface alloying technique. The micro-structure, the phase structure, the micro-hardness and the distribution of Ti concentration of alloying layer were investigated in detail by XRD, SEM and so on. The effect of process parameters on the alloying layer was studied. The experimental results show that a Ti solid solution with the precipitation Cu4Ti alloying layer has been formed on the copper surface. The thickness of the alloying layer is about 120 μm and the surface titanium concentration gradually decreases from ω （Ti） = 87% to ω （Ti） = 4%. The micro-hardness of the alloying layer is between 300 HV-800 HV. Source sputtering, surface absorption, ion bombarding and high temperature diffusion are the major factors that affect the alloying layer. 相似文献
14.
采用圆柱形和圆锥形的放电腔室,使用氢气作为放电气体在不同的射频功率下进行了放电。使用质谱诊断和Langmuir探针诊断相结合的方法对两种放电腔室中的氢等离子体的离子组分、离子能量分布（IED）、等离子体电势、电子密度和有效电子温度进行了对比研究。根据等离子体的诊断结果,讨论了圆锥形与圆柱形两种放电腔室中的放电特性。结果表明：圆柱形放电腔室中含有更多的亚稳态氢原子H *,而圆锥形放电腔室中含有更多的H+离子。圆锥形放电腔室中等离子体具有更高的电子密度和离子密度及更低的等离子体电势。 相似文献
15.
In this work, we investigated the discharge characteristics and heating mechanisms of argon helicon plasma in different wave coupled modes with and without blue core. Spatially resolved spectroscopy and emission intensity of argon atom and ion lines were measured via local optical emission spectroscopy, and electron density was measured experimentally by an RF-compensated Langmuir probe. The relation between the emission intensity and the electron density was obtained and the wavenumbers of helicon and 'Trivelpiece-Gould' (TG) waves were calculated by solving the dispersion relation in wave modes. The results show that at least two distinct wave coupled modes appear in argon helicon plasma at increasing RF power, i.e. blue core (or BC) mode with a significant bright core of blue lights and a normal wave (NW) mode without blue core. The emission intensity of atom line 750.5 nm (I ArI750.5nm) is related to the electron density and tends to be saturated in wave coupled modes due to the neutral depletion, while the intensity of ion line 480.6 nm (I ArII480.6nm) is a function of the electron density and temperature, and increases dramatically as the RF power is increased. Theoretical analysis shows that TG waves are strongly damped at the plasma edge in NW and/or BC modes, while helicon waves are the dominant mechanism of power deposition or central heating of electrons in both modes. The formation of BC column mainly depends on the enhanced central electron heating by helicon waves rather than TG waves since the excitation of TG waves would be suppressed in this special anti-resonance region. 相似文献
16.
Jiali CHEN 《等离子体科学和技术》2022,24(5):54001
Herein we report the successful preparation of silver (Ag)-decorated vertically oriented graphene sheets (Ag/VGs) via helicon wave plasma chemical vapor deposition (HWP-CVD) and radiofrequency plasma magnetron sputtering (RF-PMS). VGs were synthesized in a mixture of argon and methane (Ar/CH4) by HWP-CVD and then the Ag nanoparticles on the prepared VGs were modified using the RF-PMS system for different sputtering times and RF power levels. The morphology and structure of the Ag nanoparticles were characterized by scanning electron microscopy and the results revealed that Ag nanoparticles were evenly dispersed on the mesoporous wall of the VGs. X-ray diffraction results showed that the diameter of the Ag particles increased with the increase in Ag loading, and the average size was between 10.49 nm and 25.9 nm, consistent with the transmission electron microscopy results. Ag/VGs were investigated as effective electrocatalysts for use in an alkaline aqueous system. Due to the uniquely ordered and interconnected wall structure of VGs, the area of active sites increased with the Ag loading, giving the Ag/VGs a good performance in the oxygen evolution reaction. The double-layer capacitance (Cdl) of the Ag/VGs under different Ag loadings were studied, and the results showed that the highest Ag content gave the best Cdl (1.04 mF cm−2). Our results show that Ag/VGs are likely to be credible electrocatalytic materials. 相似文献
17.
On the basis of considering electrochemical reactions and collision relations in detail,a direct numerical simulation model of a helicon plasma discharge with three-dimensional two-fluid equations was employed to study the characteristics of the temporal evolution of particle density and electron temperature.With the assumption of weak ionization,the Maxwell equations coupled with the plasma parameters were directly solved in the whole computational domain.All of the partial differential equations were solved by the finite element solver in COMSOL MultiphysicsTM with a fully coupled method.In this work,the numerical cases were calculated with an Ar working medium and a Shoji-type antenna.The numerical results indicate that there exist two distinct modes of temporal evolution of the electron and ground atom density,which can be explained by the ion pumping effect.The evolution of the electron temperature is controlled by two schemes:electromagnetic wave heating and particle collision cooling.The high RF power results in a high peak electron temperature while the high gas pressure leads to a low steady temperature.In addition,an OES experiment using nine Ar I lines was conducted using a modified CR model to verify the validity of the results by simulation,showing that the trends of temporal evolution of electron density and temperature are well consistent with the numerically simulated ones. 相似文献
18.
Mingyang WU 《等离子体科学和技术》2022,24(5):55002
Helicon wave plasma sources have the well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies with mode transitions, which has been an outstanding issue for years. We have built a fluid simulation model and further developed the Peking University Helicon Discharge code. The mode transitions, also known as density jumps, of a single-loop antenna discharge are reproduced in simulations for the first time. It is found that large-amplitude standing helicon waves (SHWs) are responsible for the mode transitions, similar to those of a resonant cavity for laser generation. This paper intends to give a complete and quantitative SHW resonance theory to explain the relationship of the mode transitions and the SHWs. The SHW resonance theory reasonably explains several key questions in helicon plasmas, such as mode transition and efficient power absorption, and helps to improve future plasma generation methods. 相似文献
19.
A one-dimensional radial non-uniform fluid model is employed to study plasma behaviors with special emphasis laid on helicon discharges. The plasma density ne, electron temperature Te, electron azimuthal and radial drift velocities are investigated in terms of the plasma radius rp, magnetic field intensity B0 and gas pressure p0, by assuming radial ambipolar diffusion and negligible ion cyclotron movement. The results show that the magnetic confinement plays an important role in the discharge equilibrium, especially at low pressure, which significantly reduces Te compared with the case of a negligible magnetic field effect, and higher B0 leads to a greater average plasma density. Te shows little variations in the plasma density range of 1011 cm-3- 1013 cm-3 for p0 〈 3.0 mTorr. Comparison of the simulation results with experiments suggests that the model can make reasonable predictions of Te in low pressure helicon discharges. 相似文献
20.
We present here a kind of low-frequency oscillation in argon helicon discharge with a half helical antenna. This time-dependent instability shows a global quasi-periodic oscillation of plasma density and electron temperature, with a typical frequency of a few tens of Hz which increases with external magnetic field as well as radiofrequency (RF) power. The relative oscillation amplitude decreases with magnetic field and RF power, but the rising time and pulse width do not change significantly under different discharge conditions. The oscillation can only be observed in some specific conditions of low magnetic fields and low RF power when the gas flows in from one end of the discharge area and out from another end. This global instability is suggested to be attributed to the pressure instability of neutral depletion, which is the result of compound action of gas depletion by heating expansion and gas replenishment from upstream. There are two kinds of oscillations, large and small amplitude oscillations, occurring in different discharge modes. This study could be a good verification of and complement to earlier experiments. This kind of spontaneous pulse phenomenon is also helpful in realizing a pulsing plasma source without a pulsed power supply. 相似文献