有源等离子体在开放大气环境下的反应扩散过程研究

利用一维模型用数值模拟的方法,研究了低气压开放环境下大气等离子体在存在等离子体源的情况下的反应扩散过程.得到了考虑化学反应、扩散以及漂移共同作用下的大气等离子体的主要成分随等离子体注入流量的变化规律及一定流量情况下主要带电成分随时空的演化规律. 将数值模拟结果与一个近似解析公式相衔接,估计达到稳态时维持一定电子密度所需要的等离子体流量,可据此进一步估计所需功率. 关键词： 大气等离子体 等离子体源 数值模拟 反应扩散过程     

Modeling plasma loudspeakers

This paper deals with the acoustic modeling and measurement of a needle-to-grid plasma loudspeaker using a negative Corona discharge. In the first part, we summarize the model described in previous papers, where the electrode gap is divided into a charged particle production region near the needle and a drift region which occupies most of the inter-electrode gap. In each region, interactions between charged and neutral particles in the ionized gas lead to a perturbation of the surrounding air, and thus generate an acoustic field. In each region, viewed as a separate acoustic source, an acoustical model requiring only a few parameters is proposed. In the second part of the paper, an experimental setup is presented for measuring acoustic pressures and directivities. This setup was developed and used to study the evolution of the parameters with physical properties, such as the geometrical and electrical configuration and the needle material. In the last part of this paper, a study on the electroacoustic efficiency of the plasma loudspeaker is described, and differences with respect to the design parameters are analyzed. Although this work is mainly aimed at understanding transduction phenomena, it may be found useful for the development of an audio loudspeaker.     

Construction and study of a magnetoactive plasma ion source

The interaction of intense electron beams with plasmas in a nonuniform magnetic field is studied for the purpose of obtaining a magnetoactive plasma ion source. The resulting experimental data are used to trace the dynamics of the changes in the basic parameters of the source, both during the stage where it interacts with the beam and in the cooling stage. It is found that the charged particles are contained for a long time and that the efficiency of energy transfer from the beam to the source is high. This source is intended to be used for shaping and accelerating multiampere ion beams. Zh. Tekh. Fiz. 69, 44–47 (April 1999)     

超声速等离子体射流的数值模拟

基于可压缩的全Naiver-Stokes方程，利用PHOENICS程序对由会聚 辐射阳极形状等离子体炬产生的超声速等离子体射流进行了数值模拟.考虑了等离子体的黏性、可压缩性以及变物性对等离子体射流特性影响.研究了超声速等离子体射流的流场结构特性以及不同环境压力对等离子体射流产生激波结构的影响.结果表明，超声速等离子体射流在喷口附近形成的周期性激波结构是其和环境气体相互作用的结果. 关键词： 等离子体炬 超声速等离子体射流 PHOENICS     

Variation of plasma parameters in a modified mode of plasma production in a double plasma device

A modified mode of plasma production in a double plasma device is presented and plasma parameters are controlled in this configuration. Here plasma is produced by applying a discharge voltage between the hot filaments in the source (cathode) and the target magnetic cage (anode) of the device. In this configuration, the hot electron emitting filaments are present only in the source and the magnetic cage of this is kept at a negative bias such that due to the repulsion of the cage bias, the primary electrons can go to the grounded target and produce plasma there. The plasma parameters can be controlled by varying the voltages applied to the source magnetic cage and the separation grid of the device.     

Obliquely propagating ion-acoustic solitary and shock waves in magnetized quantum degenerate multi-ions plasma in the presence of trapped electrons

The properties of obliquely propagating ion-acoustic waves have been investigated in multi-ions magnetized plasma comprising of inertial, positively and negatively charged ion fluids, trapped electrons, and negatively charged stationary heavy ions. The propagation of the waves is oblique to the ambient magnetic field which is along the z-direction. Only fast type of modes exists in the linear regime. The reductive perturbation method was adopted to derive the Korteweg– de Vries (KdV) and Burger equations, as well as the solitary and shock wave solutions of the evolved equations, have been used to analyze the properties of the small but finite amplitude waves. The effects of the constituent plasma parameters, namely, the trapping effect of electrons, the electron degenerate temperature and the viscosity coefficient on the dynamics of the small amplitude solitary and shock waves have been examined. The influence of the magnetic field and the obliquity parameter on the propagation characteristics of ion-acoustic waves are discussed.     

Preparing a laser cooled plasma for stopping highly charged ions

We present a new cooling scheme for the preparation of highly charged ions for future in-trap precision experiments. A plasma of laser cooled ²⁴Mg⁺ ions trapped in a 3D harmonic confinement potential is used as a stopping medium for the highly charged ions. We focus on the dynamic evolution of the plasma, determining suitable cooling conditions for fast recooling of the ²⁴Mg⁺ ions. The results of a realistic parallel simulation of the complete stopping process presented here indicate that a small, constant detuning of the laser frequency is sufficient for subsequent recooling of the plasma, thus maintaining the stability of the plasma.     

等离子体装置中粉尘问题研究进展

等离子体装置中,带电粒子与壁材料相互作用会导致粉尘的产生。综述了主要等离子体装置中粉尘问题的实验研究现状,对主要装置中使用的诊断方法和所得到的实验结果进行了评述。提出了等离子体装置粉尘研究中存在的问题以及未来研究的方向。     

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The interactions between charged particles and wall materials produce dusts in plasma devices. Progress of dust research on the main plasma devices are reviewed, the approaches to measure dusts and the results obtained in main plasma devices in the world are presented. The unsolved problems and possible directions for further advancements are commented.     

Polymerdimethylsiloxane surface treatment with an atmospheric pressure helium plasma jet driven by unipolar nanosecond pulses

A nanosecond-pulse power source transfers energy to electrons of atmospheric pressure discharges in a nanosecond-scale rising time and shows different plasma chemistry than a slowly varying sinusoidal discharge. We report how the operation parameters, such as applied voltage, pulse duration, and repetition frequency, affect the discharge characteristics and the surface property of polydimethylsiloxane (PDMS). The applied voltage controls the energy delivery per a pulse cycle, and the repetition frequency dominantly affects the plasma density in a long-term operation. The water contact angle, the optical emission spectroscopy, and the atomic force microscope diagnostics on the PDMS are presented. While the polarity of the nano pulse bias changes the emission length of the plasma jet, the hydrophilicity is not affected by it because the chemical reactions by radicals are more dominant than the physical reactions of charged particles on PDMS.     

Feasibility study on high current ion beam extraction from anode spot plasma for large area ion implantation

In this paper, we have investigated the feasibility of the high current beam extraction from anode spot plasma as an ion source for large area ion implantation. Experiments have been carried out with the ambient plasma produced by inductive coupling with radio-frequency (RF) power of 200 W at the frequency of 13.56 MHz. Anode spot plasmas are generated near the extraction hole of 2 mm in diameter at the center of a bias electrode whose area exposed to the ambient plasma can be changed. It is found that the maximum ion beam current is extracted at the optimum operating pressure at which the area of bias electrode exposed to ambient plasma is fully covered with the anode spot plasma whose size is dominantly determined by the operating pressure for given gas species. It is also observed that the extracted ion beam current increases nonlinearly with the bias power due to the changes in size and shape of the anode spot plasma. With the well-established anode spot plasma operating at the optimum gas pressure, we have successfully extracted high current ion beam of 6.4 mA (204 mA/cm²) at the bias power of 22 W (∼10% of RF power), which is 43 times larger than that extracted from the plasma without anode spot. Based on the experimental results, criteria for electrode design and operating pressure for ion beam extraction from larger extraction aperture are suggested. In addition, the stability of anode spot plasma in the presence of ion beam extraction through an extraction hole is discussed in terms of the particle balance model.     

Thermodynamic limit in a charged plasma in equilibrium

We study the existence conditions for the thermodynamic limit in the chain of BBGKY equations for the equilibrium correlation functions of a charged plasma. It is shown that in order for the thermodynamic limit to exist the charge of the plasma cannot increase faster than the surface area of the plasma. When this condition is satisfied the equilibrium correlation functions of the charged plasma are asymptotically identical to the correlation functions of a neutral plasma in a self-consistent electrostatic field, which depends only on the one-particle correlation functions. For a plasma which is uniform everywhere except in a thin surface region, this field is found in explicit form. For a plasma occupying an infinite half-space, the problem is equivalent to a neutral plasma near a charged wall.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, 11–16, February, 1987.     

Radar studies of ionospheric dusty plasma phenomena

We discuss the influence of charged dust on radar observations in the Earth ionosphere. This region in the upper Earth atmosphere can be described as a partially ionized, low‐temperature plasma. Plasma parameters vary by orders of magnitude spatially and in time. Dust particles influence the charge balance, in some cases dusty plasma condition is met. The polar mesospheric echoes are an example of dust plasma interactions observed with radar. The mesosphere is a region where atmospheric temperature decreases with altitude and can reach frost point temperature. The formation of the polar mesospheric radar echoes involves neutral atmosphere dynamics, which is latitude dependent and it involves charged dust particles, especially icy dust that forms in the polar summer mesosphere. Charged dust can also influence incoherent scatter that results from electromagnetic waves scattering off electrons, where the electrons are coupled to other charged components. Observers rarely report charged dust signatures in the incoherent scatter spectra; we show that there is a good chance for doing so with improved observations. The incoherent scatter can possibly also be used to estimate the amount of charged dust in the direct vicinity of a meteor, as we show based on the order of magnitude considerations. This prospect of new observational results makes theoretical investigations of radio‐wave scattering in the presence of charged dust with size distributions worthwhile.     

Gd靶激光等离子体6.7nm光源的实验研究

本文对Gd靶激光等离子体极紫外光源进行了实验研究, 在 6.7 nm附近获得了较强的辐射, 并研究了6.7 nm 附近光辐射随打靶激光功率密度变化的规律以及收集角度对极紫外辐射的影响. 同时, 对平面Gd靶激光等离子光源的离子碎屑角分布进行了测量, 发现从靶面的法线到沿着靶面平行方向上Gd离子数量依次减少. 进一步研究结果表明采用0.9 T外加磁场的条件下可取得较好的Gd 离子碎屑阻挡效果.     

Characterisation of a nitrogen ECR plasma source for the MBE growth of the dilute nitride semiconductor GaAsN

The use of a nitrogen electron cyclotron resonance (ECR) plasma source has allowed the growth of GaAsN at GaAs substrate temperatures as high as 600 °C, unlike the case for growth using radio frequency (RF) plasma sources, for which there is significant loss of nitrogen at substrate temperatures as low as 480-520 °C. Photoluminescence (PL) intensities are significantly improved at a substrate temperature of 600 °C and are further improved slightly by using an ion trap to extract charged species from the beam. As the trap voltage is increased there is a reduction in the total nitrogen concentration, as measured by secondary ion mass spectrometry (SIMS), and a slight increase in the active nitrogen concentration, as measured by PL. These observations are consistent, for example, with charged and active nitrogen species together being involved in the formation of point defects, however more work is needed to clarify what may well prove to be a complex situation.     

Ion debris mitigation from tin plasma using ambient gas,magnetic field and combined effects

Mitigation of energetic ions from laser produced tin plasma is one of the principal issues in the development of an extreme ultraviolet lithographic light source. We explored the possibility of using an ambient gas and/or a magnetic field for controlling the energetic ions from tin plasma. Hydrogen, helium and argon gases provide good transmission to 13.5 nm and are found to be an effective stopper for tin ions. Absorption of in-band radiation limits the density of gas below levels needed to completely protect optics. Tin ion ranges in buffer gases were estimated using the Monte Carlo simulation code SRIM and compared with experimental results. The presence of a moderate transverse magnetic field of 0.64 T slowed the propagation of fast moving tin ions but failed to stop them. The synergistic effect of a combination of magnetic field and an ambient gas is found to be very promising for mitigating tin ions without exceeding EUV gas absorption limits. PACS 42.72.Bj; 52.50.Jm; 52.55.Jd; 52.70.kz     

Features of Electron Optical Systems with the Plasma Emitter Based on Stationary Double Electric Layers in the Plasma

Russian Physics Journal - The physical concept and the model of the construction of the plasma source of charged particles in crossed E × H fields are presented in which, due to the special...     

Characterization and investigation of the unique plasma behavior caused by variable driving frequencies in the formation of cold atmospheric plasma

The study presents the characterization of a novel variable frequency (11–50 kHz) Atmospheric Pressure Plasma Jet (APPJ) source and comparison of the results with 13.56 MHz source, in terms of species generation and species temperature. The behavior of variable frequency APPJ at different frequency regimes was investigated using optical emission spectroscopy to understand the interaction with the ambient environment. The quantitative dependence of the radical generation on driving frequency and time of treatment was also analyzed by direct synthesis of H₂O₂ by plasma-water interaction. The plasma formed with a kHz driving frequency had a low treatment temperature, which was suitable for biological species, but the plasma generated with a 13.56 MHz driving frequency had a substantially higher radical density than the kHz plasma. As a result, the APPJ device's ability to tune the radical density and treatment temperature with a change in kHz frequency has been demonstrated.