等离子体微波干涉仪的新的显示方式

等离子体微波干涉仪借微波束经过等离子体,探测由于等离子体引起的相位变化,给出等离子体平均电子线密度.在目前多种高温等离子体诊断手段中,由于微波干涉仪对等离子体干扰小,结果显示直观,操作简单方便,因而它已经成为一种常规的诊断手段.传统的微波干涉仪的工作原理如图1所示     

托卡马克微波干涉信号的实时处理

微波条纹移动干涉仪可用来测量等离子体电子密度及其分布,是一种相当有用的高温等离子体诊断工具(1).通常用干涉条纹的斑马图来直观地显示等离子体电子密度的变化,但它不能直接给出电子密度的值,因此无法用斑马图信号直接进行如密度反馈控制等物理实验.也无法将这信号经通用模数转换器用计算机采集和处理.为此有必要研制能把斑马信号实时转化为密度值的直读式处理系统. 实验中发现,由于各种原因造成微波干涉信号具有无法用模拟实验可以获得的相当复杂的扰动结构.为此我们先设计了一个专用的计算机采集系统,这样不仅能采集斑马信号,搞清干涉…     

大相移直读式微波干涉仪

一、引 言 微波法测量等离子体的电子密度通常采用 Wharton-Gardner条纹干涉仪,这种经典的条纹干涉仪对于大截面高密度的瞬变等离子体所产生的数十个2π相移变化特别是电子密度之空间分布的测量有一定的局限性。当相移超过10个2π弧度时,在示波器上读取这种干涉仪的条纹移动是很困难的。而大相移直读式微波相位测量系统能把瞬变等离子体引起的微波相移的2π弧度的数目转换成电脉冲。这些对应于密度上升和下降的2π弧度相移量的脉冲经过适当处理,既可供直读也可供计算机进行数据处理。目前该系统每500微秒可分辨2π弧度的相移。同时,它还可以利用波导桥网络的检波输出在示波器上观测条纹的移动,以便进行监测。所以它对于大型或中型托卡马克装置的测量是比较适合的。     

一种处理远红外激光干涉仪相移信号的新方法

一、引言 在等离子体物理实验中,电子密度的获取十分重要。对于中小型托卡马克装置,其密度范围正好在HCN远红外激光干涉仪(波长337μm)的可测范围,国内外许多装置都用HCN激光干涉仪来测其电子密度n_e。测量来自于干涉仪的两路信号—探测信号V_D和参考信号V_R之间的相位差即可得到n_e。密度相移信号的产生及与n_e的对应关系、传统测量相位差的方法已有专文叙述。传统处理方法由于存在相移过2π时计数值的跳变问题,在密度起伏较频繁     

HL-2M 装置 CO2 色散干涉仪研制

研制了一套新型 CO₂ 激光色散干涉仪用于 HL-2M 装置初始放电期间的电子密度测量。该系统采用 基于激光倍频的色散测量原理,能够消除机械振动产生的相位误差。该系统使用全新的调相式信号调制,研发了 相应的数据采集/处理/上传系统。根据实验测量结果表明,CO₂ 激光色散干涉仪和微波干涉仪测量曲线基本一致, 色散干涉仪系统的测量精度约为 2×10¹⁷m⁻³,密度测量上限能达到 10²¹m⁻³。     

HL-2A装置偏滤器中的微波干涉仪测量

微波干涉仪测量等离子体电子密度是一种常规监测工具，利用这种工具可以给出电子密度随时间变化的波形图。等离子体电子密度和微波干涉仪测出的相位差之间的关系为：     

HT-7五道HCN激光干涉仪光学元件的设计

介绍了电磁波在等离子体中的传播以及用外差干涉的方法测量托卡马克装置等离子体电子密度的原理。详细讨论了在 HT- 7超导托卡马克上用于密度诊断测量的五道 HCN激光干涉仪光路的主要光学元件 ,如各类分束片、托卡马克密度诊断窗口的尺寸和厚度的设计以及光学材料的选择 ,并在实验中得到了很好的结果 ,验证了设计的合理性和准确性。五道的位置分别为沿小环圆截面 - 2 0 cm、- 10 cm、0 cm、+ 10 cm、+ 2 0 cm。     

微波反射获得密度振动谱

本文描述用微波反射法测量等离子体中的低频密度扰动的原理和方法。给出在HL-1托卡马克上测到的初步结果,并和静电探针的结果作了比较。     

转镜调制二氧化碳激光干涉仪

耦合腔干涉仪是在激光器出现后才发展起来的新型干涉仪。由于其光路简单,易于调整,对等离子体无干扰等优点,已成为稠密等离子体密度测量的常用工具。如所周知,耦合腔激光干涉仪对等离子体电子密度测量的灵敏度为:     

微波干涉仪测量等离子体电子密度

由于微波在等离子体中传播时其幅度和相位都随着等离子体状态的变化而变化， 因而可利用微波干涉仪测量等离子体的动态电子密度．     

Magnetic phase diagram in a quasi-two-dimensional electron gas

Using spin density functional theory within the framework of the local spin density approximation with Perdew-Zunger type exchange-correlation energy, ferromagnetism in a quasi-two-dimensional electron gas (Q-2DEG) is studied. The electronic and magnetic structures of a thin film are calculated as a function of film thickness and electron density. Ferromagnetism in the Q-2DEG is found to appear at a higher electron density than in the three-dimensional electron gas. Unless a film is very thin, with decreasing electron density, a magnetic phase transition occurs from a spin-unpolarized fluid to a Wigner film with surface magnetism, in which the spin polarization localizes only in the neighborhood of surfaces. Further decreasing density induces another transition to a fully spin-polarized ferromagnetic Wigner film.     

Spatial distribution of electron characteristic in argon rf glow discharges

The spatial distributions of the electron density and the mean electron energy of argon radio frequency (rf) glow discharge plasma in a plasma-enhanced chemical vapour deposition (PECVD) system have been investigated using an established movable Langmuir probe. The results indicate that in the axial direction the electron density tends to peak at midway between the two electrodes while the axial variation trend of mean electron energy is different from that of the electron density, the mean electron energy is high near the electrodes. And the mean electron energy near the cathode is much higher than that near the anode. This article focuses on the radial distribution of electron density and mean electron energy. A proposed theoretical model distribution agrees well with the experimental one: the electron density and the mean electron energy both increase from the centre of the glow to the edge of electrodes. This is useful for better understanding the discharge mechanism and searching for a better deposition condition to improve thin film quality.     

以一定重复频率工作的KTP倍频效率的演化规律

基于导带电子密度和材料的有效介电函数的表达式,推导了KTP晶体对532 nm光波的吸收系数. 对比研究了不同峰值功率密度和重复频率下KTP晶体的导带电子密度和532 nm吸收系数的演化规律,以及倍频转换效率的演化规律. 结果表明,随着导带电子密度的增加,KTP晶体532 nm吸收系数随之增加,其倍频转换效率随之减小;当基频光入射功率密度一定时,不同重复频率脉冲作用引起的导带电子密度存在积累效应,导致KTP晶体532 nm透过率及倍频转换效率均随着作用时间的增加呈指数形式变化,随着脉冲重复频率的增加其积累效果更加明显,但随着作用时间的增加,导带电子密度、吸收系数均趋于同一稳定值. 关键词： KTP晶体 灰迹 倍频转换效率     

Coherent spin dynamics of different density high mobility two-dimensional electron gas in a GaAs quantum well

We have addressed the dependence of quasi-two-dimensional electron spin dephasing time on the electron gas density in a 17-nm GaAs quantum well using the time-resolved magneto-optical Kerr effect. A superlinear increase in the electron dephasing time with decreasing electron density has been found. The degree of electron spin relaxation anisotropy has been measured and the dependence of spin-orbit splitting on electron gas density has been determined.     

Effects of relativistic and ponderomotive nonlinearities on the interaction of high-power laser beam with an inhomogeneous warm plasma

The influence of relativistic-ponderomotive nonlinearities and the plasma inhomogeneity on the nonlinear interaction between a high-power laser beam and a warm underdense plasma are studied. It is clear that the relativistic ponderomotive force and the electron temperature modify the electron density distribution and consequently change the dielectric permittivity of the plasma. Therefore, by presenting the modified electron density and the nonlinear dielectric permittivity of the warm plasma, the electromagnetic wave equation for the propagation of intense laser beam through the plasma is derived. This nonlinear equation is numerically solved and the distributions of electromagnetic fields in the plasma, the variations of electron density, and plasma refractive index are investigated for two different background electron density profiles. The results show that the amplitude of the electric field and electron density oscillations gradually increase and decrease, during propagation in the inhomogeneous warm plasma with linear and exponential density profiles, respectively, and the distribution of electron density becomes extremely sharp in the presence of intense laser beam. It is also indicated that the electron temperature and initial electron density have an impact on the propagation of the laser beam in the plasma and change the plasma refractive index and the oscillations' amplitude and frequency. The obtained results indicate the importance of a proper choice of laser and plasma parameters on the electromagnetic field distributions, density steepening, and plasma refractive index variations in the interaction of an intense laser beam with an inhomogeneous warm plasma.     

氧负离子解吸附过程HPM大气击穿弛豫时间分析

基于全局模型,引入氧负离子解吸附过程,完善了重复频率高功率微波脉冲弛豫模型,理论研究了重复频率高功率微波脉冲大气击穿弛豫过程,数值模拟了不同附着频率、解吸附频率以及初始电子浓度条件下,弛豫过程电子浓度随时间的变化规律。结果表明:弛豫过程电子浓度变化分为快衰减和慢衰减两个阶段;发现氧负离子的引入明显延缓了弛豫过程后期电子的衰减;解吸附频率与附着频率对弛豫过程有着相反的影响,解吸附频率越高,慢衰减阶段的电子浓度越高,快衰减阶段电子浓度变化不明显;附着频率越高,快衰减阶段电子浓度变化越剧烈,慢衰减阶段的电子浓度越低;初始电子浓度越大,慢衰减阶段电子浓度变化越剧烈。     

Calculation of the Effect on the Reflection of the Plane Electromagnetic Wave for Non-Magnetized Plasma with Different Electron Density Distributions

In this paper, shift operator finite-difference time-domain (SO-FDTD) method is applied for the calculation of the dispersive medium. The high efficiency and accuracy of this method is verified by calculating the reflection of the plane electromagnetic wave impinging on a non-magnetized plasma slab with different electron density distributions. The results show that the average electron density only determines overall trends of the reflection, and different distributions affect the oscillating process of the reflection. If the average electron density maintains the same, the distribution of electron density with homogenous or inhomogeneous alternation will sharply take effects on the reflection. And magnitude of alternation of electron density affects the incident frequency directly when the reflection tends to uniform.     

大面积等离子体片密度分布分析

利用空心阴极放电产生了尺寸为60 cm× 60 cm× 2 cm的大面积等离子体面. 在实验室条件下对大面积等离子体片的密度分布进行了测量. 由于高压放电脉冲脉宽较短, 实验中改变了测量方法, 同时, 在中等磁场影响下, 为了得到真实的等离子体密度, 进行了必要的数值修正.在放电电流为1---6 A时, 测量了二维的电子密度分布. 另外, 测量并讨论了其他环境参数对等离子体密度的影响. 电子密度的分布情况对与微波波束切换相当重要. 由空心阴极增强型放电产生的大面积等离子体面具有反射X波段(8---12 GHz) 微波需要的足够稠密的电子密度和足够均匀的密度分布, 这是等离子体面在雷达系统中取代金属面板的有利条件.     

Optical pumping of nuclear spin magnetization in GaAs/AlAs quantum wells of variable electron density

We report the use of time-resolved Faraday rotation to induce and probe the polarization of nuclear spins within a set of quantum wells with varying background electron density. The electron density was controlled over a broad range by making use of structures of mixed type-I/type-II GaAs/AlAs quantum wells that spatially separate photoexcited electron–hole pairs. We find that the optically detected nuclear magnetic field decreases quasi-monotonically with increasing electron density. The likely factors responsible for this behavior are increased electron spin-lattice relaxation, increased electron spin delocalization, and dilution of the electron spin polarization.     

Measurement of electron density distribution in the probe of a low voltage SEM

A method for measuring the electron density distribution in the probe of a low voltage scanning electron microscope is described. It is shown that the focused electron probe of an S 4800 scanning electron microscope at the electron energy of 200 eV has a Gaussian shape of the electron density with the effective diameter of the probe of 20 nm.