Investigations of the spatio-temporal build-up of atomic oxygen inside the micro-scaled atmospheric pressure plasma jet

The ascent of atomic oxygen densities created inside the micro-scaled atmospheric pressure plasma jet has been investigated spatially resolved under parameter variations such as applied power, gas mixture and gas velocity using two-photon absorption laser induced fluorescence spectroscopy. Along the discharge channel an increase of the atomic oxygen density within the plasma is observed. The density shows an exponentially asymptotic convergence into an equilibrium close to the effluent. In the post-discharge effluent an exponential spatial decrease can be found. Typical ascent distances of a few hundreds of μm decrease with the applied power and increase with gas velocity and oxygen admixture. The maximum atomic oxygen density increases with applied power and admixed molecular oxygen up to more than 10¹⁶ cm^-3. An increase of the maximum atomic oxygen density with increasing gas velocity has been found. Optical emission spectroscopy measurements indicate a strong increase of the nitrogen emission at low gas flow rates along the channel.     

局域环境中微波等离子体电子密度诊断实验研究

为了研究局域真空环境中微波等离子体喷流电子数密度的分布规律及其影响因素,利用发射/郎缪尔探针测量等离子体的空间电位,再测量等离子体的电流-电压特性曲线,根据空间电位测量结果,在等离子体的电流-电压特性曲线上能准确地获取饱和电流,从而处理出电子数密度.最后的诊断实验表明：在有约束边界条件下,微波等离子体发生器以60 W以下的微波功率击穿流量范围是21—105 mg/s的氩气时,所产生的喷流中电子数密度分布在8.8×10¹⁴—7.53×10¹⁶/m^{3关键词： 等离子体诊断技术 等离子体基本过程 等离子体基本特性}     

Analysis of the behavior of a discharge in a coaxial plasma jet accelerator

We analyze the behavior of the discharge in a coaxial plasma jet accelerator with a pulsed supply of the working gas released by an electric discharge from titanium hydride powder. Radiation (varying with time) from the discharge in the accelerator was detected using an optical method through a narrow slit cut along the outer electrode by a Bifo Company K008 streak camera. Stable operation of the source with the highest kinetic energy of a pure hydrogen plasma jet was attained for a relatively uniform glow of the discharge along the accelerator during the entire current pulse. Conversely, local glow of the discharge at the outlet or inlet of the accelerator considerably contaminated the discharge with impurities, and the kinetic energy of the plasma jet decreased by an order of magnitude. The highest energy of the plasma jet was attained when the polarity of the electrodes was the same as at the plasma focus.     

On the Stark broadening of the He I 447.1 nm spectral line

Characteristics of the Stark broadened and overlapping 447.1 nm He I spectral line and its forbidden 447.0 nm components have been measured at electron densities between 4.4×10²² m^-3 and 8.2×10²² m^-3 and electron temperatures between 18 000 K and 33 000 K in plasmas created in five various discharge conditions using the low pressure pulsed arc as an optically thin plasma source operated in helium-nitrogen-oxygen gas mixture. Good agreement was found among our measured line characteristics and their existing calculated values, based on the quasistatic approximation. Possible influence of the singly ionized oxygen impurity atoms (O II) on the intensity values of the dip between allowed and forbidden components was found that can explain the disagreement among some existing experimental and calculated line characteristics data, at higher electron temperatures and densities. On the basis of the observed asymmetry of the 447.1 nm spectral line profile we have obtained the ion contribution parameter at 10²² m^-3 electron density and 8 000 K electron temperature. Received 20 February 2001 and Received in final form 25 April 2001     

Experiment on the electromagnetic radiation excited in an electron beam‐ion channel system

An experimental study on electromagnetic (EM) radiation in an electron beam‐ion channel system is reported, which indicates the same result predicted by our previous theory. The system is formed in an arc plasma jet with a plasma density of 10¹⁷m^?3 , and the electron beam is driven by a voltage pulse of 20 kV. The result shows that the system can excite EM radiation in the range of the plasma frequency. The scheme is also hopeful to be used for generating high‐frequency and wide‐band EM radiation up to terahertz by enhancing the plasma density.     

真空中微波等离子体喷流电子数密度分布规律实验研究

为了准确诊断真空中微波等离子体喷流的电子数密度，利用统一的发射和单郎缪尔探针测量等离子体的空间电位，再测量等离子体的电流-电压特性曲线.根据空间电位测量结果，在等离子体的电流-电压特性曲线上能准确地获取饱和电流，从而处理出电子数密度.最后的诊断实验表明，当真空环境压强为2—6 Pa、等离子体发生器以60 W以下的微波功率击穿流量范围是42—106 mg/s的氩气时，所产生的微波等离子体喷流中电子数密度分布在1×10¹⁶—7.2×10¹⁶/m³范围内.     

OH number densities and plasma jet behavior in atmospheric microwave plasma jets operating with different plasma gases (Ar,Ar/N<Subscript>2</Subscript>, and Ar/O<Subscript>2</Subscript>)

OH radical number density in multiple atmospheric pressure microwave plasma jets is measured using UV cavity ringdown spectroscopy of the OH (A–X) (0–0) band at 308 nm. The plasma cavity was excited by a 2.45 GHz microwave plasma source and plasma jets of 2–12 mm long were generated by using three different plasma gases, argon (Ar), Ar/N₂, and Ar/O₂. Comparative characterization of the plasma jets in terms of plasma shape, stability, gas temperature, emission intensities of OH, NO, and N₂, and absolute number density of the OH radical was carried out under different plasma gas flow rates and powers at various locations along the plasma jet axis. With three different operating gases, the presence of OH radicals in all of the plasma jets extended to the far downstream. As compared to the argon plasma jets, the plasma jets formed with Ar/N₂ and Ar/O₂ are more diffuse and less stable. Plasma gas temperatures along the jet axis were measured to be in the range of 470–800 K for all of the jets formed in the different gas mixtures. In each plasma jet, OH number density decreases along the jet axis from the highest OH density in the vicinity of the jet tip to the lowest in the far downstream. OH density ranges from 1.3 × 10¹² to 1.1 × 10¹⁶, 4.1 × 10¹³ to 3.9 × 10¹⁵, and 7.0 × 10¹² to 4.6 × 10¹⁶ molecule/cm³ in the Ar, Ar/N₂, and Ar/O₂ plasma jets, respectively. The OH density dependence on plasma power and gas flow rate in the three plasma jets is also investigated.     

Experimental plant for investigation of the possibility of linac-based production of medicine-intended isotopes

We describe a technique of obtaining radioactive ^99mTc isotope by irradiation of molybdenum with high-intensity beam of bremsstrahlung photons from the electron beam of the linear electron accelerator (LUE50) of the Alikhanyan National Science Laboratory (ANSL, former Yerevan Physics Institute). We have elaborated and created an experimental plant for development of ^99mTc production technology. Upgrading of linac has been performed aimed at raising the beam intensity and density. A system of automated control of the parameters of the plant and accelerator was built up. We carried out preliminary studies of ^99mTc obtaining technique and give quantitative and qualitative results.     

Study of an Underexpanded Plasma Jet

Supersonic jets (Mach number M = 1.4 – 2.0) of dense plasma were produced by a plasmatron in a pulsed regime. The shock structure was investigated by fast mirror cameras, by the schlieren technique and by probe and spectroscopic methods. It was found that during jet expansion the bow shock ahead the gas-plasma interface and the shock behind it are superimposed with the quasistationary shock structure which includes the Mach disk. Whereas the plasma in the discharge chamber is in LTE (n_E ≈ 5 × 10²³ m^?3, T ≈ 14000 K), the electron density of the expanding jet plasma falls to a plateau value of n_E ≈ 5 × 10¹⁹ m^?3 below the LTE limit. At this phase, the jet plasma formed a ball-like turbulent plasmoid which moves at a subsonic velocity through the air up to some milliseconds.     

Study on the RF Power Necessary to Ignite Plasma for the ICP Test Facility at HUST

An Radio‐Frequency (RF) Inductively Coupled Plasma (ICP) ion source test facility has been successfully developed at Huazhong University of Science and Technology (HUST). As part of a study on hydrogen plasma, the influence of three main operation parameters on the RF power necessary to ignite plasma was investigated. At 6 Pa, the RF power necessary to ignite plasma influenced little by the filament heating current from 5 A to 9 A. The RF power necessary to ignite plasma increased rapidly with the operation pressure decreasing from 8 Pa to 4 Pa. The RF power necessary to ignite plasma decreased with the number of coil turns from 6 to 10. During the experiments, plasma was produced with the electron density of the order of 10¹⁶m^–3 and the electron temperature of around 4 eV. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Independent UHF plasma source and possibility of filling open magnetic trap

A stationary UHF plasma source, its characteristics and possibility of filling open magnetic trap with plasma injected from it have been described. Plasma is created in the source at frequency of 2400 MHz (supplied power is up to 150 W) in the electron cyclotron resonance (ECR) regime under working gas pressure 10^–5–10^–2 Torr. By changing discharge conditions one can change the injected plasma density from 10⁹ to 10¹² cm^–3, at the temperatureT _e=2–10 eV. The possibility of efficient plasma injection from the source into the open magnetic trap of various configurations is shown experimentally. Plasma characteristics in the trap are presented under various experimental conditions. It is established that plasma parameters can be easily changed in the trap.     

On the Stability of Ballooning Modes in the Boundary Layers of a Gas Insulated Plasma

In order to fulfill power density requirements in future steady-state fusion reactors the ion density in central parts must be of the order 10²⁰–10²¹–m^?3. In such systems high density neutral gas may surround the hot plasma, whether introduced on purpose or not, provided the neutral gas flux from the plasma is not continuously removed by external means. In gas insulated plasmas large density and pressure gradients will arise close to the boundaries on account of plasma neutral gas interaction effects. In this paper the stability of gravity driven ballooning modes in the boundary region is investigated. In particular, the coupling between plasma and neutral gas investigated in previous stability analysis is reconsidered. Also effects previously neglected for example the Nernst effect is taken into account.     

Target plasma formation by UHF power

The properties of plasma injected into an open magnetic trap of uniform field from an independent UHF source have been investigated. Plasma is created in the UHF source at the frequency of 2400 MHz (power input 150 W) in the electron cyclotron resonance (ECR) regime at the pressure of neutral argon (10⁻⁵−10⁻²) torr. It is established that a rather quiescent target plasma with controlled density within the range of (2 × 10⁸−2 × 10¹²) cm⁻³ and temperature 2–3eV is accumulated in the trap. It turned out that plasma lifetime in the trap is determined by a classical mechanism of particle escape at the expense of collisions, at fixed value of magnetic field in the trap it practically is not changed with the variation of neutral gas pressure and reaches the value ≈ 4×10⁻³ s at the magnetic field strength in the trap equal 1600 Oe.     

Generation of Large‐Area Highly‐Nonequlibrium Plasma in Pure Hydrogen at Atmospheric Pressure

Diffuse Coplanar Surface Barrier Discharge (DCSBD) is a novel type of atmospheric‐pressure plasma source developed for high‐speed large‐area surface plasma treatments. Basic characteristics of DCSBD operated in pure atmospheric‐pressure hydrogen were measured using optical and emission spectroscopy methods, and its potential for the surface treatment application was demonstrated by hydrogen plasma reduction of Cu₂O thin layers. The discharge generates a thin layer of diffuse non‐equilibrium plasma with a high power density of 70 Wcm^–3. The mean electron density and electron temperature derived from spectroscopic data were 1.3 x 10¹⁶cm^–3 and 19 x 10³K, and the surface Cu₂O layers forming a weak boundary were reduced to metallic copper within several seconds. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Development,creation, and startup of the DC-110 heavy ion cyclotron complex for industrial production of track membranes

The DC-110 heavy ion cyclotron for industrial production of track membranes has been developed and created at the Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research. The cyclotron is equipped with an electron cyclotron resonance ion source operating at a frequency of 18 GHz. The accelerator complex was put into operation in 2012 and ⁴⁰Ar⁶⁺, ⁸⁶Kr¹³⁺, and ¹³²Xe²⁰⁺ ion beams with a energy of 2.5 MeV/nucleon and intensity of 13, 14.5, and 10.5 μA, respectively, were produced. Irradiation of a polymer film was carried out on a specialized channel and track membranes with a high uniformity of pores were obtained. The DC-110 accelerator complex can produce up to 2 million square meters of track membranes per year.     

电推力器等离子体喷流对航天器通讯电磁波信号衰减效应

采用时域有限差分法计算了不同特性电推力器等离子体喷流对不同频率通讯电磁波的衰减系数,采用空间透射波法进行了微波等离子体推力器喷流对C波段电磁波衰减的地面测试实验。理论计算和实验诊断结果表明:电推力器等离子体喷流对电磁波的衰减系数随着电磁波频率的升高逐渐减小,随着喷流等离子体频率的升高近似线性增大,随着喷流等离子体碰撞频率的增大呈先增大后减小的趋势;当喷流中等离子体数密度为0.9×1016~1.8×1016m-3时,C波段电磁波的衰减系数为1.5~6.0 dB,电推力器等离子体喷流对通讯信号的衰减效应不可忽略。     

同轴枪放电等离子体电流片的运动特性研究

同轴枪放电可以产生高速度、高密度的等离子体射流,在天体物理、核物理等研究领域具有广泛的应用.基于同轴枪放电等离子体运动的"雪犁模型"分析,本实验通过对等离子体光电信号和磁信号的测量及放电照片的拍摄,研究了不同放电电流和气压对同轴枪放电等离子体电流片的运动特性、电流通道分布的影响.实验结果发现:一次放电过程中,气压为10 Pa、放电电流为35.7—69.8 kA时,随着放电电流的增加,等离子体喷射速度增加,输运距离与离子携带的轴向动能成正比,大电流条件下,等离子体喷出枪口时易于在枪底端形成新的电流通道;气压为5—40 Pa、放电电流为49.8 kA时,随着气压的增加,等离子体喷射速度减小,输运距离缩短,高气压下,等离子体喷出枪口时在枪底端未产生新的放电通道,这与放电过程中遗留在枪底端的带电粒子和电流片渗漏残留在枪内的中性粒子共同形成的阻抗通道有关;电流反向时,二次放电击穿位置发生在电极头部,放电过程中存在多次放电现象.     

An Innovative Simple Method for Study of the Characteristics of the Trigatron Plasma Switch

A simple Semi‐Analytical method used to fit the experimentally recorded current of the closed switch discharge circuit into the free running under damped LC oscillator model and the arc plasma conductivity, electron density of the plasma and efficiency of the spark gap switch energy transfer have been driven from the model by some simple calculations. The charging voltage, switch pressure and the spark gap has been changed between 6 to 15 kV, 1 to 1.5 bar and 1.4 or 2.8 mm, respectively. The obtained values for plasma conductivity and electron density of plasma are (5‐25)(Ω mm)^–1, (0.5–3.5)·10²⁴m^–3, respectively. The efficiency of the switch is plotted Vs. Pd and E/P which in both cases the peak value has been about 80 present.     

Plasma pencil — A new small scale source for atmospheric surface modifications

Plasma pencil is a device which can produce plasma jet at atmospheric pressure and low power (10–200 W) from DC to HF. The jet character of the plasma makes this device very efficient in aimed local (1 – 10² mm²) modifications of surfaces. Great variability in possible power sources allow to achieve a broad range of effects on materials. We have tested bipolar discharges with a metal object and a unipolar HF discharge to burn the glazing on ceramics. Both technologies could be prospective.