Millimeter-Wave Spectroscopy of Kr-CO and Xe-CO Using a Coaxial Jet Spectrometer

A new pulsed supersonic jet millimeter-wave spectrometer with coaxial propagation of the molecular jet and millimeter-waves has been constructed. The coaxial configuration provides greater sensitivity which has been demonstrated by observing b-type transitions of five isotopomers of Kr-(12)C(16)O and seven isotopomers of Xe-(12)C(16)O. These results were analyzed together with a-type transitions obtained by FTMW spectroscopy to determine improved rotational parameters for each isotopomer. The ground vibrational state K = 1 <-- 0 intervals have thus been precisely determined for Kr-CO and Xe-CO. Copyright 2001 Academic Press.     

Measurement of Mach probe on plasma flow velocity in highly collisional plasma jet

A normalized plasma flow velocity in highly collisional plasma formed by a microwave plasma jet, which is dimensionless unit for plasma flow velocity/ion acoustic velocity, was measured by the parallel Mach probe. To deduce the normalized plasma flow velocity under highly collisional plasma conditions, the collisional model of a Mach probe was proposed. In addition, neutral gas flow velocity which assumed to be plasma flow velocity was calculated by the turbulent model. The results for the two different models were compared with those for the collsionless models of the Mach probe. The turbulent model produced 2–4 times reduced values than by measurements with collsionless models. The measured results with the collisional model were shown as approximately 100–250% lower than those for collsionless models. They were obtained to be in good agreement with difference rate of 10–30% when compared to those for the turbulent model.     

Excitation of the Potential Relaxation Instability in a Weakly Magnetized Discharge Plasma by a Voltage Step

An instability is triggered in a weakly magnetized discharge plasma by the application of a positive voltage step to a planar collector immersed into the plasma column with its surface perpendicular to the magnetic field lines. Time developement of the plasma density after the application of the pulse is measured by a Langmuir probe. Radial and axial velocity of the plasma density perturbation are measured. Radial velocity is consistent with the increase of the plasma potential in the current channel. Axial velocity is very high. It is interpreted as phase velocity of radial quasiperiodic motion of the plasma in and out of the current channel. Response time of the collector current to the applied voltage step is measured versus different parameters. Experimental results are in agreement with a qualitative model presented in previous work [1] where the observed instability is modeled as a two dimensional potential relaxation instability (PRI). Minor improvements of the previous model are proposed. A rarefaction pulse that moves towards the collector is found as the initial stage of the instability.     

Diagnostics of Langmuir oscillations in a superdense plasma

The level and the angular distribution of Langmuir oscillations in a dense plasma produced on the Phoenix plasma radiation source (PRS) were measured. Line profiles of several lines in the Lyman series of Al XIII were measured using crystal spectrometers. A spectral line shape model was used, which attempted to take into account all significant broadening mechanisms. The parameters of the plasma and the Langmuir oscillations were found by generating profiles using the model and comparing these profiles to the experimental spectra. The strength of the Langmuir oscillations was found to be E₀≈1-9 GV/cm, indicative of a strong Langmuir turbulence. The polarization analysis of the profiles of the Al XIII Lyman γ line has shown that the Langmuir oscillations develop anisotropically, primarily in the direction of the plasma current     

A Model of the Multicathode-Spot Vacuum Arc

A model is proposed for the multicathode-spot (MCS) vacuum arc. A zero-order model is filrst constructed, whereby the interelectrode plasma is produced by the multitude of cathode spots, and flows to the anode upon which it condenses. The electron density is calculated by assuming that the plasma is uniform within a cylinder bounded by the electrodes and using expenmental data for the ionic velocities and ion current fraction obtained in single cathode spot arcs. The electron density thus obtained is proportionate to the current density, and is equal to 5 × 1020 m-3 in the case of a 107-A/m2 Cu arc. The model predictions are a factor of 3-4 lower than measured values. First-order perturbations to the zero-order model are considered taking into account inelastic electron-ion collisions, plasma-macroparticle interactions, the interaction of the self-magnetic field with the plasma and electric current flows, and the interaction with the anode. Inelastic collisions tend to increase the ionicity of the plasma as a function of distance from the cathode, in agreement with spectroscopic observations. Macroparticles are heated by ion impact until they have significant evaporation rates. The vapor thus produced is ultimately ionized, and most probably accounts for the discrepancy between the zero-order prediction of electron densities and the measured values. Constrictions near the anode in both the plasma and electric current flows have been calculated. An overabundant electron current supply forces the anode to assume a negative potential with respect to the adjacent plasma.     

A forced gas-cooled single-disk window using silicon nitride composite for high power CW millimeter waves

Silicon nitride composite as a candidate of a window material for high power CW (Continuous Wave) millimeter-waves was high power tested especially with a surface cooling by impinging gas nitrogen jets on the single-disk surface. Gas-cooling dramatically suppressed the temperature of the window disk even with gas flow rate of around 100 l/min. With gas cooling of 465l/min., 130kW CW power of HE₁₁ mode could be transmitted through the silicon nitride window with a diameter of 88.9mm. The peak window temperature was completely saturated on 123.6 °C. Without gas-cooling it did not saturate and reached 323 °C during 30 seconds pulse. A possibility of 1MW CW single disk Brewster windows with a forced gas-cooling is discussed, resulting in convinced prospects of the windows with realistic size and thickness.     

Analysis of the Evolution of a Supersonically Expanding Plasma

A supersonically expanding arc plasma in argon is analyzed both experimentally and theoretically. The plasma is created in a cascaded arc and extracted through a hole in the anode. It emanates in a large vacuum system, where it expands supersonically. This expansion is limited by a shock wave. After the shock wave a subsonic plasma beam is created. A quasi one-dimensional model, based on the conservation of mass, momentum and energy is presented. The shock wave is treated as a discontinuity. The electron density, the gas velocity and the gas temperature are measured as a function of the position in the expansion by means of Stark broadening and Doppler spectroscopy. The model calculations agree well with the measurements, especially in the first part of the supersonic flow.     

Strong reduction of the degree of spatial coherence of a laser beam propagating through a preformed plasma

A strong reduction of the spatial coherence of a laser beam after its propagation through a plasma has been measured using a Fresnel biprism interferometer. The laser beam was diffraction limited; the coherence width was reduced from 40 mm in vacuum down to a few mm with the plasma. Numerical results based on a paraxial model exhibit a coherence degree close to the experimental one; they also prove the importance of taking into account the nonlocal transport effects in numerical simulations for such plasma conditions.     

Eine Bemerkung zum Verhalten von Glimmentladungen bei Brennspannungsänderungen im Nanosekundenbereich

A previous experimental investigation showed that the short time behaviour of glow discharges at fast changes of Cathode potential is determined by a damped plasma oscillation in the negative glow. A simple oscillation model brought satisfactory agreement between the measured quantities and those determined by this model. Only the plasma densities were 10 times smaller than the experimental values obtained by other methods. In this work it is shown that taking into account the cathode dark space in a manner analogue to the treatment of the sheath capacities in the theory of the plasma resonance probe gives correct values of densities, too.     

A model for the shell current in a reversed field pinch

A model for the shell current in a reversed field pinch which includes the current induced by the motion of the plasma is discussed. This model gives a good approximation to the magnitude and time dependence of a shell current measured experimentally     

基于双光注入锁定1550 nm垂直腔表面发射半导体激光器产生可调谐毫米波

基于自旋反转模型, 对双光注入下1550 nm 垂直腔表面发射半导体激光器(1550 nm-VCSEL)的非线性动力学行为进行了理论分析和数值仿真研究. 结果表明: 当一个中心波长位于1550 nm 的副VCSEL(S-VCSEL)同时受到来自两个主VCSELs (M-VCSELs)的光注入时, 在适当的注入条件下, S-VCSEL可处于双光注入锁定态. 此时, S-VCSEL中的两偏振模式均呈现频率为两注入光频率之差的周期性振荡, 输出的光谱仅包含两个主频率部分, 即光谱具有单边带特征. 因此, 基于双光注入下S-VCSEL的周期性振荡可以获得两个相互正交的光毫米波. 通过调节两个M-VCSELs之间的频率差异可使毫米波频率在较大范围内连续可调, 通过调节系统参量可以控制毫米波功率以及调制深度. 关键词： 垂直腔表面发射激光器 双光注入 毫米波 调制深度     

The electron current to a Langmuir probe in a flowing high-pressureplasma

The electron current to a Langmuir probe in a moving high-pressure plasma has been measured and analyzed. The plasma is an atmospheric-pressure propane flame, and the probe's speed relative to the plasma was varied from 10 ms^-1 to 30 ms^-1. The current is linearly dependent on the speed and appears to be comprised of two components-one driven by diffusion and the other by convection. A model is devised which can be used to measure the electron density. By comparing the density computed from this model to that measured from the ion current, it has been possible to measure the electron mobility in the flame gases. The value obtained by the authors is in good agreement with theoretical calculations found in the literature     

等离子体显示大面积闪烁的客观评价

针对等离子体显示普遍存在的大面积闪烁现象,提出了一种基于时变光信号亮度测量系统的大面积闪烁客观评价方法。时变光信号亮度测量系统利用光电管和亮度计,实现了对显示屏输出光信号亮度值随时间变化的快速、准确记录。基于阴极射线管显示临界闪烁频率估算模型,通过主观视觉感知实验,利用测量系统得到亮度随时间的变化关系,建立了平均感知闪烁程度估算模型。估算模型输出结果与视觉感知实验数据相关系数达到0.98。该测量系统与估算模型实现了对等离子体显示大面积闪烁的客观度量,并与主观视觉感知实验结果相吻合,是等离子体显示屏优化设计和显示行业标准建立的有效工具。     

Influence of the glass-to-plasma boundary layer in a t-tube on continuum radiation

A possible influence of a boundary layer between the plasma and a shock tube wall on the Paschen continuum intensities has been checked for a simple boundary-layer model. The results show that the measured continuum intensities, with a boundary layer thinner than 1 mm, may differ appreciably from intensities measured when the thickness of the boundary layer is negligible. It has also been shown that there is a temperature for every electron density when the continuum intensity is independent of the boundary-layer thickness provided it is small compared with the plasma radius.     

Structure of magnetic fields generated in laser produced plasmas

A numerical model is used to interpret recent results on magnetic fields generated in laser plasma experiments. Satisfactory agreement is found between model predictions and experimental observations of the morphology of the field. The principal features of the measured density profile are also reproduced.     

Interaction of nanosecond laser pulses with plastic foams

Some results of an experimental and theoretical study of the interaction of laser pulses with plastic foams are reported. The propagation velocity of a hydrodynamic peturbation which was initiated in foam target under the action of a laser pulse with intensityq≈2·10¹³ W/cm² and the velocity distribution function of plasma ions were measured; the preliminary results of time-integrated spectroscopic measurements of an intense red-shifted signal are also reported. A self-consistent model of the foam target’s laser plasma formed in a hydrodynamic mode was derived. The predictions of this model are consistent with experimental results. A model of microprocesses of laser plasma formation in a structured material was also developed. The results of numerical simulations by 1D and 2D computer codes are also reported. Original article submitted in English May 25, 1997.     

Sheath motion in a capacitively coupled radio frequency discharge

The sheath motion in a capacitively coupled RF discharge is highly nonlinear. The voltage waveform on a cylindrical probe placed in the sheath region is measured as a function of position and time. A circuit model of the probe-discharge system relates the observed probe voltage to the sheath motion. The equations derived from this circuit model are solved numerically with varying nonlinear sheath motions; the resulting waveforms are compared with the experimental observations to determine the actual sheath motion. The time-varying plasma potential is also determined, indirectly, from the comparison. The authors also report observation of oscillations related to the plasma frequency, whose peak harmonic component can be calculated from a single plasma model. These oscillations can be a useful plasma diagnostic for determining plasma density. The presence of these high-frequency oscillations may significantly enhance the rate of stochastic heating of electrons     

Modeling plasma equipment using neural networks

Equipment plasma has been modeled semi-empirically using neural networks in conjunction with statistical experimental design. A 3³ factorial design was employed to characterize the plasma, in which the variables that were varied include a source power, pressure, and Ar flow rate. As a test data for model validation, 16 experiments were additionally conducted. A total of six plasma attributes were modeled, which include electron density, electron temperature, and plasma potential as well as their spatial uniformities. A planar, inductively coupled plasma was generated in a multipole plasma etch equipment and Langmuir probe was utilized for data collection. Root mean-squared prediction errors measured on the test data are 0.323 (10 ¹¹/cm³), 0.267 (eV) and 1.141 (V) for electron density, electron temperature, and plasma potential, respectively. Comparisons with a statistical response surface model (RSM) revealed that neural network models are more accurate by an improvement of more than 25% in prediction performance. A similar level of prediction accuracy was also achieved in modeling spatial uniformity data. Consequently, neural networks demonstrated much better prediction capabilities over RSM in modeling complex equipment plasma     

Energy Selecting Action of Limiters on Particle Fluxes Penetrating into the SOL-Plasma

A simple model of the penetration of particle effluxes from the core plasma into the SOL-plasma of tokamaks is proposed. The assumptions made are free streaming of particles parallel to the magnetic field and anomalous particle transport perpendicular to the toroidal field with a constant radial velocity. The model has been proved for measured particle fluxes of Li which was injected into the core plasma of the tokamak T-10. The dependence of the Li-particle flux on the minor radius as well as toroidal asymmetries in the SOL-plasma can be explained by the results of the calculations.