Fast-axial-flow CO2-laser with integrated turbo-blower

A new type of CO₂-laser with high-power capability is described. It employs fast axial flow driven by a high-frequency radial impeller. Due to the coaxial design which integrates discharge tube, blower, and gas cooler into a single cylindrical housing, a very compact laser unit is realized. The discharge is rf excited (13.56 MHz). With a specific input power of 21 W/cm³ an output of 800 W is generated at an efficiency of 16%. The discharge can easily be operated in a pulsed mode with frequencies up to 10 kHz.     

Thermal Analysis Simulation of Germanium Zone Refining Process Assuming a Constant Radio-Frequency Heating Source

Three-dimensional thermal analysis simulation of a horizontal zone refining system is conducted for germanium semiconductor materials.The considered geometry includes a graphite boat filled with germanium placed in a cylindrical quartz tube.A flow of Ar and H_2 gas mixture is purged through the tube.A narrow section of the boat is assumed to be exposed to a constant heat rate produced by an rf coil located outside the quartz tube.The results of this analysis provide essential information about various parameters such as the shape of the molten zone,required power and temperature gradient in the system.     

Longitudinal rf discharge in Xe/Cl<Subscript>2</Subscript> mixtures

Results are presented from the studies of the electrical and emission characteristics of the low-temperature plasma of a longitudinal rf (f₀=1.76 MHz) discharge in Xe/Cl₂ mixtures at pressures of 100–800 Pa. The discharge was ignited in a cylindrical quartz tube with an inner diameter of 1.4 cm and interelectrode distance of 3.0 cm. The discharge emission within the spectral range of 190–670 nm is studied. The dynamics of the discharge current and discharge emission at different pressures and compositions of a Xe/Cl₂ mixture are investigated. It is shown that a discharge in a Xe/Cl₂ mixture acts as a wideband excimer-halogen lamp with a cylindrical output aperture emitting in the spectral range of 220–320 nm. The broad plasma emission spectrum is formed due to the overlap of the XeCl(D, B-X; B, C-A) bands that are broadened at low working-gas pressures. The composition of the working mixture is optimized to achieve the maximum power of the wideband UV plasma emission. Longitudinal rf discharges in low-pressure Xe/Cl₂ mixtures are of interest for developing small-size wideband (Δλ=220–450 nm) cylindrical-aperture lamps, whose efficiency can, on average, exceed the efficiency of conventional hydrogen lamps by more than one order of magnitude.     

Deeply undercritical microwave discharge excited by the field of a quasi-optical electromagnetic beam in a supersonic air jet

Electric discharge in a supersonic air jet is studied. It is ignited in a linearly polarized quasi-optical microwave electromagnetic beam the initial field intensity of which is much lower than the breakdown level. Electric breakdown is initiated by a tubular electromagnetic vibrator, one end of which has spikes and is covered by a quartz tube. Atmospheric air enters into a low-pressure working chamber through the inner channel of the vibrator. As a result, an immersed supersonic air jet forms in the chamber at the outlet from the quartz tube. A microwave discharge ignited in this jet is “attached” to aft spikes of the vibrator. The energy deposit into the discharge plasma and the effective area of energy interaction between the discharge and excited microwave field are estimated from the temperature and stagnation pressure distributions in the wake of the discharge.     

气体激光器放电等离子体管的新设计

文中分析了常用气体激光器采用园柱形放电管时所存在的弊端,提出了按照光腔类型和模体积来设计放电等离子体管的原理。从而可提高激光器的基模输出功率(TEMoo)。文中给出了管型的设计程序和成形工艺,讨论了具有模体积几何形状放电等离子体管的特性。     

Moving striations in tapered discharge tube

Moving striations in the tapered tube with smoothly changing radius are studied experimentally. The frequency depends on local tube radius by nature and increases toward the narrow end of the tube, independent of direction and magnitude of the discharge current. Radius-frequency versus radius-pressure is compatible with the similarity law for striations in cylindrical tubes. When there appears synchronization, the frequency becomes apparently constant throughout the tube column. The wavelength shows different dependences on radius without and with the synchronization. An important role is played by the feedback through an electric circuit. Also, direction and magnitude of the current have influence on the phenomena. Steady states in the tubes are compared with those in cylindrical tubes. An attempt is made to explain the observed synchronizations and then the remarkable discrepancies between the previous experiments can be eliminated.     

Simulation of radio-frequency atmospheric pressure glow discharge in γ mode

The existence of two diffe1：ent discharge modes has been verified in an rf （radio-frequency） atmospheric pressure glow discharge （APGD） by Shi [J. Appl. Phys. 97, 023306 （2005）]. In the first mode, referred to as a mode, the discharge current density is relatively low and the bulk plasma electrons acquire the energy due to the sheath expansion. In the second mode, termed γ mode, the discharge current density is relatively high, the secondary electrons emitted by cathodc under ion bombardment in the cathode sheath region play an important role in sustaining the discharge. In this paper, a one-dimensional self-consistent fluid model for rf APGDs is used to simulate the discharge mechanisms in the mode in helium discharge between two parallel metallic planar electrodes. The results show that as the applied voltage increases, the discharge current becomes greater and the plasma density correspondingly increases, consequentially the discharge transits from the a mode into the γ mode. The high collisionality of the APGD plasma results in significant drop of discharge potential across the sheath region, and the electron Joule heating and the electron collisional energy loss reach their maxima in the region. The validity of the simulation is checked with the available experimental and numerical data.     

A KrF-laser excited by a capacitively coupled longitudinal discharge

The performance of a KrF excimer laser, excited by a discharge produced in a quartz tube between two metallic electrodes at its end and the inner tube wall serving as a dielectric electrode, is described. The dielectric electrode is capacitively coupled to a metallic electrode surrounding the quartz tube coaxially. Laser output energies up to 0.9 mJ in pulses having a duration of 6 ns FWHM could be obtained at a driving voltage of 100 kV.     

Numerical study on the gas heating mechanism in pulse-modulated radio-frequency glow discharge

The gas heating mechanism in the pulse-modulated radio-frequency(rf) discharge at atmospheric pressure was investigated with a one-dimensional two-temperature fluid model. Firstly, the spatiotemporal profiles of the gas temperature(T_g)in both consistent rf discharge and pulse-modulated rf discharge were compared. The results indicated that T_gdecreases considerably with the pulse-modulated power, and the elastic collision mechanism plays a more important role in the gas heating change. Secondly, the influences of the duty cycle on the discharge parameters, especially on the T_g, were studied.It was found that T_gdecreases almost linearly with the reduction of the duty cycle, and there exists one ideal value of the duty cycle, by which both the T_gcan be adjusted and the glow mode can be sustained. Thirdly, the discharge mode changing from α to γ mode in the pulse-modulated rf discharge was investigated, the spatial distributions of T_gin the two modes show different features and the ion Joule heating is more important during the mode transition.     

Characterization of CN<Subscript>x</Subscript>/SiO<Subscript>y</Subscript> films prepared by the inductively coupled RF discharge

Hard films were deposited in an inductively coupled rf discharge at the frequency of 3.5MHz by the chemichal transport of carbon from the graphite target in nitrogen atmosphere combined with the evaporation of a quartz tube. The nitrogen flow varied from 1.0 to 4.0 sccm. The supplied rf power was in the range of 3 kW. Silicon substrates were placed on the graphite holder whose temperature was 750°C. The films had the hardness of 35GPa maximum and they showed high elastic recovery up to 88%, good fracture toughness and adhesion to the substrate. The hardness of deposited films increases with increasing CN_x/SiO_y ratio. This ratio is influenced by the deposition time.     

石英管对空气中锥-板结构纳秒脉冲放电的影响

报道了石英管对大气压下空气中锥-板电极结构纳秒脉冲放电的影响实验研究.实验过程中发现将石英管纵向移动位置,放电会出现四种明显不同的形貌状态,对其机理进行了初步的探讨.利用发射光谱诊断了其转动和振动温度(分别为295和2200 K),表明该等离子体具有高度非平衡度.还进一步提出大气压下空气中产生类辉光放电的有效途径. 关键词： 纳秒脉冲放电 空气 纵向介质 非平衡等离子体     

Formation of a quasi-hollow beam of high-energy heavy ions using a multicell resonance RF deflector

The generation of matter in an extreme state with precisely measurable parameters is of great interest for contemporary physics. One way of obtaining such a state is to irradiate the end of a hollow cylindrical shell at the center of which a test material is kept at a temperature of several Kelvin by an annular beam of high-energy heavy ions. Under the action of the beam, the shell starts explosively expanding both outwards and inwards, compressing the material to an extremely high pressure without subjecting it to direct heating. A method of producing a hollow cylindrical beam of high-energy heavy ions using a resonance rf deflector is described. The deflection of the beam in two transverse directions by means of an rf electric field allows it to rotate about the longitudinal axis and irradiate an annular domain on the end face of the target.     

Features of the α-γ transition in a low-pressure rf argon discharge

It is found that the region for the stable existence of the aregime of a radio-frequency (rf) discharge is bounded not only on the moderate-pressure side, but also on the low-pressure side. One feature of the α-γ transition in a low-pressure rf discharge is that the criterion for breakdown of the electrode sheath is not satisfied. It is shown that at low pressures the α-γ transition of an rf argon discharge takes place abruptly and exhibits hysteresis. At intermediate pressures the α-γ transition is continuous and lacks jumps; negative differential conductivity appears, double layers form, and nonmonotonic behavior of the plasma density is observed at the center of the discharge. The role of stochastic (collisionless) electron heating in sustaining an rf discharge at intermediate gas pressures is discussed. Zh. Tekh. Fiz. 68, 52–60 (May 1998)     

A stationary filamentary microwave discharge at a high pressure of argon

A stationary discharge in the form of a filament about 1 mm in diameter is produced in a quartz tube 16 mm in diameter passed through the wider wall of a standard waveguide and field with argon at a pressure of 300 mm Hg at a microwave power of 50 W on a frequency of 7 GHz. The number of filaments increases gradually from one to seven as the power and pressure are increased. The filaments are parallel and oriented along the electric field of the wave. They are arranged symmetrically relative to the equatorial plane of the tube. The distance between the filaments decreases as their number increases. The stationary filaments arising due to ionization-overheating instability may be explained qualitatively using the interference-equilibrium model and assuming that a discharge is organized such as to provide for the maximal power absorption.     

Emissivity of the pulsed capacitive discharge in helium-iodine and neon-iodine mixtures

The emission parameters of a pulsed capacitive discharge initiated in helium-iodine and neon-iodine mixtures are reported. The discharge plasma emits at wavelengths of 183.0 and 206.2 nm, which correspond to iodine atom spectral lines. The capacitive discharge is initiated in a cylindrical quartz tube with an electrode distance of 10 cm. The discharge radiation is optimized in exciting pulse repetition rate and helium and neon pressures in He(Ne)-I₂ mixtures. The optimal pressures of helium, neon, and iodine vapor fall into the ranges 0.8–2.0 kPa, 0.5–1.0 Pa, and ≤60 Pa, respectively.     

Structure of ion-acoustic oscillation spectrum in high-current discharge plasma

The approximate dispersion laws for the normal modes of LF ion-acoustic oscillations in a cylindrical positive column are found. The oscillation spectra and correlation functions of high-current discharge ionic spontaneous emission are measured as a function of the plasma parameters and the tube length and diameter. They confirm the ion-acoustic nature of the oscillations. The mode structure of the spectra caused by a radial nonuniformity of the ion-laser plasma is detected for the first time.     

气压对微束射频容性放电模式调制的研究

微束射频容性放电在纳米晶体颗粒等离子体增强气相合成有着潜在的应用前景.本论文利用ICCD、单反相机、高压探头和电流探头等对微束射频容性放电特性进行了实验诊断研究.结果发现:在纯氩气微束射频放电中,随着气压的增加,放电从辉光放电模式向多通道丝状放电模式转换;在99%氩/1%氢混合气体微束射频放电中,丝状放电模式消失,而是从低气压全空间分布的辉光放电模式,到中等气压向轴心收缩的辉光放电模式,最后到高气压的“环状”辉光放电模式;而在纯氢气微束射频放电中,随着气压的增加,放电模式直接从全空间分布的辉光放电模式向“环状”辉光放电模式转换.最后通过射频电场中电子加热、趋肤效应和气体热传导的共同作用解释了产生不同放电模式的物理机制.     

氮气射频放电与直流放电PIC/MC模拟的比较

建立氮气容性射频等离子体过程的PIC/MC模型,将模拟结果与直流放电进行比较.结果表明:射频等离子体粒子(e,N₂⁺,N⁺)的平均密度较直流放电约大-个量级,在射频电极附近粒子(e,N₂⁺,N⁺)的平均能量比直流放电阴极附近的能量低3倍左右;密度偏低的原子离子N⁺在两电极附近具较高的能量,能量较低的分子离子N₂⁺在放电空间具较高密度,N₂⁺的密度大约是N⁺的6倍;计算的电子能量几率分布与测量结果-致.     

Switching characteristics of the triggered vacuum gap for ahigh-repetition-rate pulse-power source

Switching characteristics of sealed-off triggered vacuum gaps (TVGs) were examined from the viewpoint of a high repetition rate at high current discharge. With a triggered energy of 11 J, it was possible to fire the main gap in both the anode and cathode modes of operation. In repetitive discharge experiments, the TVG-tube was put in the center of the cylindrical conductor and the switching tube inductance was about 27 nH. The TVG-tube was confirmed to have capabilities for 1000 shots with a pulse current of 120 kA and a high repetition rate of 5 Hz. These experimental results indicated that the TVG-tube is a potential repetitive closing switch for the plasma X-ray source     

Air flow control around a cylindrical model induced by a rotating electric arc discharge in an external magnetic field. Part I

The structure and dynamics of a near-wall gas flow produced by a rotating electric arc discharge in an external magnetic field around a cylindrical model without an incoming flow has been investigated. The electric arc on the model has been produced by a combined electric discharge (low-current rf discharge + high-current pulse-periodic discharge). Permanent magnets with induction B ≈ 0.1 T have been placed inside the cylindrical models. Ring electrodes are arranged on the surface of the model. The structure and dynamics of the near-wall gas flow around the cylindrical model have been investigated using high-speed photography, as well as the shadowgraph and particle image velocimetry (PIV) methods.