Measurement of neutral gas temperature in inductively coupled plasmas

Dependence of the neutral gas temperature on the gas pressure and discharge power in an inductively coupled plasma source has been investigated using optical emission spectroscopy. Both nitrogen and argon plasmas have been studied separately. In the case of argon plasma, about 5% nitrogen was added to the total gas flow as an actinometer. The maximum temperature was found to be as high as 1850 K at 1 Torr working pressure and 600 W radiofrequency power. The temperature increases almost linearly with the logarithm of the gas pressure, but changes only slightly with the discharge power in the range of 100–600 W. In a nitrogen plasma, a sudden increase in the neutral gas temperature occurs when the gas pressure is increased at a given discharge power. This suggests a discharge-mode transition from the H-mode (high plasma density) to the E-mode (low plasma density). In the H-mode, the gas temperature is proportional to the logarithm of the gas pressure, as in the argon plasma. However, the gas temperature increases almost linearly with the discharge power, which is in contrast to the case of argon plasma. The electron density in the nitrogen plasma is about 10% of that in the argon plasma. This may explain the observation that the nitrogen neutral temperature is always lower than the argon neutral temperature under the same discharge power and gas pressure.     

Characteristics of a large gap uniform discharge excited by DC voltage at atmospheric pressure

A large-gap uniform discharge is ignited by a coaxial dielectric barrier discharge and burns between a needle anode and a plate cathode under a low sustaining voltage by feeding with flowing argon. The basic aspects of the large-gap uniform discharge are investigated by optical and spectroscopic methods. From the discharge images, it can be found that this discharge has similar regions with glow discharge at low pressure except a plasma plume region. Light emission signals from the discharge indicate that the plasma column is invariant with time, while there are some stochastic pulses in the plasma plume region. The optical emission spectra scanning from 300 nm to 800 nm are used to calculate the excited electron temperature and vibrational temperature of the large-gap uniform discharge. It has been found that the excited electron temperature almost keeps constant and the vibrational temperature increases with increasing discharge current.Both of them decreases with increasing gas flow rate.     

Reaching high poloidal beta at Greenwald density with internal transport barrier close to full noninductive current drive

In the ASDEX Upgrade tokamak, high poloidal beta up to beta(pol) = 3 at the Greenwald density with H-mode confinement has been reached. Because of the high beta, the plasma current is driven almost fully noninductively, consisting of 51% bootstrap and 43% neutral beam driven current. To reach these conditions the discharge is operated at low plasma current ( I(P) = 400 kA) and high neutral beam heating power ( P(NBI) = 10 MW). The discharge combines an edge (H mode) and internal transport barrier at high densities without confinement-limiting MHD activities. The extrapolation to higher plasma currents may offer a promising way for an advanced scenario based fusion reactor.     

Measurement of the interaction potential of microspheres in the sheath of a rf discharge

The interaction potential of two microspheres that are levitated in the sheath region of a radio frequency (rf) argon discharge is studied experimentally by analyzing their trajectories during head-on collisions. It is shown that the interaction parallel to the sheath boundary can be described by a screened Coulomb potential. Thus, values for an effective charge and a screening length can be obtained. The horizontal part of the interaction potential has been determined for several plasma conditions. There is no evidence for an attractive part in the potential within the accuracy of the present measurements and the given plasma conditions.     

Soot elimination and NOx and SOx reduction indiesel-engine exhaust by a combination of discharge plasma and oildynamics

The soot in the exhaust gas from a 2-L diesel-engine car has been eliminated almost completely, independent of the load and cruising speed, by a plasma reactor mounted downstream of the engine exhaust and a novel technique using a combination of discharge plasma and oil dynamics. The NO_x (NO₂+NO) and SO_x components have also been reduced by about 70% at a rotational speed of 1200 rpm and a load of 7 kg-m, corresponding to about 60% of maximum torque (about 11.4 kg-m at 1200 rpm). The reduction rate of NO_x in this investigation is about 20% more efficient than ordinary treatment using a discharge plasma only     

Low power gas discharge plasma mediated inactivation and removal of biofilms formed on biomaterials

The antibacterial activity of gas discharge plasma has been studied for quiet some time. However, high biofilm inactivation activity of plasma was only recently reported. Studies indicate that the etching effect associated with plasmas generated represent an undesired effect, which may cause live bacteria relocation and thus contamination spreading. Meanwhile, the strong etching effects from these high power plasmas may also alter the surface chemistry and affect the biocompatibility of biomaterials. In this study, we examined the efficiency and effectiveness of low power gas discharge plasma for biofilm inactivation and removal. Among the three tested gases, oxygen, nitrogen, and argon, discharge oxygen demonstrated the best anti-biofilm activity because of its excellent ability in killing bacteria in biofilms and mild etching effects. Low power discharge oxygen completely killed and then removed the dead bacteria from attached surface but had negligible effects on the biocompatibility of materials. DNA left on the regenerated surface after removal of biofilms did not have any negative impact on tissue cell growth. On the contrary, dramatically increased growth was found for these cells seeded on regenerated surfaces. These results demonstrate the potential applications of low power discharge oxygen in biofilm treatments of biomaterials and indwelling device decontaminations.     

基于DBD 悬浮电极低温等离子体杀菌消毒仪研制

基于介质阻挡放电(DBD)原理,研究设计了一种悬浮电极式的低温等离子体发生设备,产生的等离子体温度较低且对人体安全,可直接接触。用所研制的低温等离子体发生设备对大肠杆菌做了灭活实验,实验结果表明,该设备产生的低温等离子体对大肠杆菌作用10s 以上,在等离子体有效作用区内大肠杆菌杀灭率为100%,表明所研制的低温等离子体发生设备具有很好的杀菌消毒效果。     

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基于介质阻挡放电(DBD)原理,研究设计了一种悬浮电极式的低温等离子体发生设备,产生的等离子体温度较低且对人体安全,可直接接触。用所研制的低温等离子体发生设备对大肠杆菌做了灭活实验,实验结果表明,该设备产生的低温等离子体对大肠杆菌作用10s 以上,在等离子体有效作用区内大肠杆菌杀灭率为100%,表明所研制的低温等离子体发生设备具有很好的杀菌消毒效果。     

Silcone Catheter Sterilization by Microwave Plasma; Argon and Nitrogen Discharge

Sterilization capability of 2.45GHz Electron Cyclotron Resonance plasma system on silicone catheter is investigated for Ar and N2 gas discharges. E.coli, MRSA, Basillus cereus and Bacillus subtilis bacteria infected silicone catheter pieces are tested for sterilization. Basillus subtilis, which is a spore type bacteria, is determined as the most resistant one, and non spore type bacteria, Escherichia coli, is determined as the easiest one. The results show that nitrogen -N2 discharge has better sterilizing effects than Ar discharge by 15% less in time. Doubling the applied microwave source power decreases sterilization time scanty. Sterilization of silicone catheter is less than an hour for above bacteria types. Plasma discharge sterilization preserves the chemical integrity of polymer — based instruments.     

Measurement of Temperature and Density Profiles of the Plasma at PR-2 Facility

A new system of probe diagnostics at linear plasma simulator PR-2 is described, allowing us to measure the profiles of plasma temperature and density in different cross sections of the plasma column. The Langmuir probe fixed to the movable part of the two-coordinate positioning system built into the PR-2 passes the region of the discharge area during the process of measuring plasma parameters. The overall dimensions of the positioning system make it possible to mount electrical probes (magnetic probes, optical fibers, and other diagnostic equipment) covering almost the entire volume of the vacuum chamber between the magnetic mirrors of the device. We present the measurement results of local plasma parameters of the beam-plasma discharge (BPD) for different values of the input power and working gas pressure. The boundaries of appearance of discharge of three types were determined: the diffusive BPD mode, the BPD mode, and the arc mode. Dependences of the plasma concentration and temperature on the input power for different values of pressure have been also determined.     

空心针-板电极大气压氩气辉光放电的特性研究

大气压均匀放电等离子体在工业领域具有非常广泛的应用前景,它是利用直流电源激励的空心针-板放电装置,以氩气为工作气体在大气压空气中产生均匀稳定的放电。对氩气流量和气隙间距对辉光放电发光特性的关系进行了研究,结果表明放电所产生的等离子体柱连接两个电极,发光较为均匀(观察不到放电丝)。在板电极附近放电等离子体柱直径最大,最大直径随着电流和气流的增大而增大。放电伏安特性研究发现,与低气压辉光放电相类似,两电极间的电压随着电流的增大而减小,并且随气流和气隙间距的增大而增大。对该大气压直流均匀放电在扫描范围为330～450 nm的光学发射光谱进行分析,获得了放电等离子体的分子振动温度和谱线强度比I_391.4/I_337.1随氩气流量和气隙间距的变化关系。I_391.4/I_337.1均随流量和气隙间距的增大而降低。对等离子体柱的I_391.4/I_337.1沿气流方向(等离子体柱轴向)进行了空间分辨测量,并进行了定性分析,结果表明,振动温度及电子平均能量随着远离空心针口距离的增大而增大。这些结果对大气压辉光放电在工业中的应用具有重要意义。     

Spatial variation behaviors of argon inductively coupled plasma during discharge mode transition

A Langmuir probe and an ICCD are employed to study the discharge mode transition in Ar inductively coupled plasma. Electron density and plasma emission intensity are measured during the E (capacitive discharge) to H (inductive discharge) mode transitions at different pressures. It is found that plasma exists with a low electron density and a weak emission intensity in the E mode, while it has a high electron density and a strong emission intensity in the H mode. Meanwhile, the plasma emission intensity spatial (2D image) profile is symmetrical in the H mode, but the 2D image is an asymmetric profile in the E mode. Moreover, the electron density and emission intensity jump up discontinuously at high pressure, but increase almost continuously at the E to H mode transition under low pressure.     

Profile of spectral-line intensity along a negative glow

The longitudinal profile of the spectral-line intensity has been measured in a plasma of a negative glow in helium, neon, and mixtures of these gases. Under the conditions of a normal glow discharge, the intensities of several spectral lines fall off exponentially toward the anode. The decay of the line intensity was used to evaluate the effective cross section for attenuation of the electron beam from the cathode dark space. There is a discussion of the mechanism for the change in the profile of the line intensity in the discharge gap at the transition on a normal glow discharge to an anomalous discharge.     

Glow Discharge Characteristics of Hollow Needle-Plate Electrode in Atmospheric Pressure ArgonSCIEI北大核心CSCD

Atmosphere pressure uniform plasma has the broad application prospect in the industrial field. Using hollow needle cathode - plate anode device excited by direct-current voltage, a uniform and stable glow discharge is generated at atmospheric pressure in ambient air with argon used as working gas. The influence of the experimental parameters (including gas flow rate and the gas gap width) on discharge has been investigated by optical method. It can be found that a glow-discharge plasma column can bridge the two electrodes. The plasma column is uniform, and no filaments can be discerned. Near the plate electrode, the diameter of the plasma column is largest of all positions. The maximal diameter of the plasma column increases with increasing the discharge current or the gas flow rate. Through electrical method, the voltage-current characteristic has been investigated. It has been found that the discharge voltage decreases with increasing the current which is similar with the characteristic of glow discharge in low pressure. It increases with increasing the gas gap width or the gas flow rate. By analyzing the optical emission spectrum scanning from 330 to 450 nm emitted from the direct-current glow discharge, the molecular vibrational temperature and the intensity ratio of spectral lines I-391.4/I-337.1 have been investigated as functions of the gas flow rate and gas gap width. Results indicate that both the vibrational temperature and the intensity ratio of spectral lines I-391.4/I-337.1 decrease with increasing the gas flow rate or the gas gap width. In addition, the molecular vibrational temperature and the intensity ratio of spectral lines I-391.4/I-337.1 have been investigated in spatial resolution along the direction of gas flow(plasma column axial), and give a qualitative analysis as well. It is found that the vibrational temperature and the average electron energy increase with increasing the distance from the hollow needle cathode. These results are important to the industrial applications of glow discharge.     

Voltage current and power relation in an arc plasma in a variable axial magnetic field

The variation of voltage, current and output power in a mercury arc plasma has been investigated in an axial magnetic field (0–1350 G) for three values of discharge current namely 3, 4 and 5 A. The voltage increases and current decreases almost linearly and the output power also increases with increase of the magnetic field. The conductivity value in magnetic field has been calculated and an analytical expression presented to represent the variation of conductivity in the magnetic field. Utilizing this expression the variation of output power with magnetic field can be explained.     

Macroscopic cell experiments and three-dimensionalmodelling on electrode-shaping plasma display cell

A macroscopic cell and three-dimensional fluid model have been used to investigate the discharge characteristics in ac plasma display panel cells of electrode-shaping configurations. Four kinds of non-standard geometries (i.e. $D$-, ${\it\del}$-, $W$- and $U$-shape electrodes) have been considered. The characteristics of the discharge current, the operating voltage and the discharge efficiency of different configurations have been discussed. It is found that the discharge efficiency can be improved by about 10\%--30\% compared with the standard geometry, while the operating voltage increases slightly in the non-standard geometries. There is a trade-off between improving the discharge efficiency and lowering the sustaining voltage in design of plasma display cells by electrode shaping.     

Dusty plasma structures in magnetic fields in a dc discharge

The formation of dusty plasma structures has been experimentally investigated in a cylindrical dc discharge in axial magnetic fields up to 2500 G. The rotation of the dusty plasma structures about the discharge symmetry axis with a frequency depending on the magnetic field has been observed. When the field increases to 700 G, the displacement of dust particles from the axial region of the discharge to the periphery, along with the continuation of the rotation, has been observed. The kinetic temperatures of the dust particles, the diffusion coefficients, and the effective nonideality parameter have been determined for various magnetic fields. The explanation of the features in the behavior of the dust particles in the discharge in the magnetic field has been proposed on the basis of the analysis of ambipolar diffusion in the magnetized plasma. The maximum magnetic field at which the levitation of the dust particles in the discharge is possible has been estimated.     

Flow control with plasma-based actuator in different velocity regimes: Momentum and heat transfer effects

In this study, control of the airflow by the direct current (DC) electrical discharge with bare electrodes has been investigated in different velocity regimes. The discharge characteristics of the plasma model are obtained numerically. An induced electrohydrodynamic (EHD) force on neutral flow was characterized based on momentum transfer from charged particles. The change in the incident flow parameters was studied by applying Navier–Stokes (N-S) equations, considering source terms arising from a weakly ionized plasma. The effect of the discharge on the low- and high-speed flow was simulated in this study. It was concluded that the changes of the velocity profile, airflow pressure, and oblique shock wave could be attributed to the EHD force from a nonthermal plasma to the incoming airflow. It was seen that the incident airflow is accelerated also by the induced EHD force. Our results show that the most important mechanism in the plasma-based flow control is the momentum transfer from the electrical discharge to the incident flow and that the gas heating has no significant role.     

高速时空分辨光谱仪的构建及其在水中纳秒脉冲火花放电光谱诊断中的应用

近年来对水中高压脉冲放电等离子体特性的诊断研究越来越受到重视。测量单个放电脉冲放电等离子体的时间-空间分辨发射光谱,有助于研究水中脉冲放电等离子体的时空演化动力学特性和规律。在本研究中将四分幅超高速相机和单色仪结合,构建了一种跟踪单个放电脉冲的高速时空分辨光谱仪,开发了相应的光谱分析软件。用波长632.8 nm的He-Ne激光器,在1 200 g·mm-1刻线光栅条件下对光谱仪的性能进行了测试。结果表明：对应He-Ne氦氖激光632.8 nm谱线的像素分辨率为0.013 nm。在曝光时间20 ns时,单色仪狭缝宽度0.2 mm时632.8 nm谱线的仪器展宽为(0.150±0.009)nm,仪器展宽随着狭缝宽度的增加呈现增大趋势。曝光时间的变化不会引起仪器展宽的变化,能够确保在调节相机曝光时间的过程中不影响光谱仪性能。利用该高速分辨光谱仪对水中纳秒火花放电发射光谱进行了测量,单次曝光获得了单一脉冲放电等离子体时空演化光谱。今后进一步完善实验室的电路条件消除放电干扰,可以对单个放电脉冲进行更细致的测量,为研究单个放电脉冲等离子体参数的时空演化特性提供良好的技术手段。     

A theoretical formula of E-H discharge transition power in atransformer-coupled discharge

Based on the recently developed heating theory (see Yoon et al., Phys. Rev. E, vol.55, no.6, p.7536-48 (1997)), a theoretical formula of E- and H-discharge transition power in a transformer-coupled plasma (TCP) discharge has been developed. The present result agrees well with an experimental observation for argon discharge