电子回旋共振离子源等离子体的密度测量

 诊断电子回旋共振离子源等离子体的传统方法是采用传统的单探针无发射时测量伏安曲线,并根据曲线的拐点由理论公式计算出的等离子体密度。本文设计并研制了等离子体密度的测量装置。采用单根朗缪尔探针（该探针可以用来发射电子）测量等离子体的伏安特性。在探针有发射和无发射两种状态下测量得到两条伏安曲线,根据这两条曲线的"分叉点"得到等离子体电位,然后根据该电位直接由计算机计算出电子温度、电子密度。采用该新方法,测量得到的等离子体参量空间电位约为17 V,悬浮电位约为-5 V,电子温度约为4.4 eV,离子密度为1.10×10¹¹cm^-3,与传统方法计算出的等离子体1.12×10¹¹cm^-3相比,两者相差仅1.8％,但新方法效率和精度更高。     

Langmuir双探针诊断Ne辉光放电管电子密度

应用Langmuir双探针诊断理论,对充有氖气的石英放电管中的辉光放电等离子体进行了诊断,通过实验测得伏安特性曲线,计算得出电子温度和电子密度,讨论了等离子体的宏观参量与电子温度和电子密度的关系.采用直径为0.1 mm的探针对等离子体进行诊断,不仅减小了对所测等离子体区域的扰动,而且减小了读取伏安特性曲线所带来的误差.     

LEAD螺旋波射频等离子体电子能量分布函数的测量

通过电压扫描探针测量了LEAD装置螺旋波射频等离子体伏安特性曲线和电子能量分布函数,并对等离子体基本参数剖面如电子温度、密度、等离子体电位和鞘电位降系数等进行了计算.实验发现在LEAD装置半径5cm以内的位置电子能量分布函数都遵循麦克斯韦分布.而在半径7cm附近,即与射频源线圈处于相同径向位置,电子能量呈现出典型的双麦...     

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用HL-2A装置下偏滤器靶板上的14组嵌入式静电三探针阵列和外偏滤器室的电动扫描四探针组,测量了同一环向截面的内外中性化板上的电子温度、密度、悬浮电位及其分布,以及电子回旋加热(ECRH)实验期间的等离子体行为。研究了偏滤器中等离子体参数的分布及非对称性以及等离子体的形成、物理特性和改善粒子的约束特性。     

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}     

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.     

超高速碰撞LY12铝靶产生膨胀等离子体云的电导率测量

 为了研究超高速碰撞过程中产生的膨胀等离子体云的电导率,设计了适用于瞬态等离子体电导率测量的扫描电探针系统。通过二级轻气炮加载LY12球形铝弹丸,运用设计的扫描电探针系统分别进行了相同入射角度和不同碰撞速度条件下超高速碰撞产生等离子体电导率的实验测量。通过对探针等效电路的分析,获得了在整个物理过程中给定探针位置处产生膨胀等离子体云的电导率随时间的变化关系。实验结果表明：在碰撞角度(与靶板平面的夹角)相同、传感器布局相同的条件下,碰撞速度越大,产生膨胀等离子体云的电导率相对越大。     

HL-2A等离子体边缘的快速单探针测量

介绍了对HL-2A装置中平面边缘等离子体的单探针测量。单探针是安装在可径向移动、并可绕轴旋 转360o的传动杆上的。在1MHz的快速采样频率下,测量了主等离子体边缘的温度、密度、悬浮电位、空间电位、极 向等离子体流速的径向分布。测量的结果表明,利用单探针测量的主等离子体边缘参数与朗缪尔四探针测量结果 基本一致。     

KT-5C托卡马克上不同限制器偏压下等离子体p约束改善的实验研究

在KT-5C托卡马克上,采用多块组合的可偏压限制器控制等离子体边缘电场.进行了改善等离子体的边缘参数及其机制的研究.实验显示,限制器的正、负偏压都能改变等离子体电位,但正偏压更有效,能有效地建立边缘电场,进而抑制边缘扰动改善等离子体约束.利用可移动静电探针,测得正偏压期间边缘电子温度T_e(r)、电子密度n_e(r)、空间电位V_p(r)分布变陡,与计算得到的边缘粒子通量Г(a_(?))减少,整体粒子约束时间τ_p增加结果是一致的.     

Langmuir探针诊断低压氢等离子体电子密度与温度

为研究实验参数对螺旋波诱导的低压氢等离子体状态的影响,用Langmuir探针对等离子体伏安特性曲线进行了原位诊断,采用双曲正切函数的指数变换模型拟合曲线,根据Druyvesteyn方法得到状态参数电子密度、有效电子温度和电子能量几率函数,分析了它们随实验参数的变化规律。结果表明:射频输入功率、气压和约束磁场对等离子体状态有较大影响。随着射频射入功率增大,放电模式发生转变,电子密度跳跃增长;随着气压增大,电子密度先增大后减小,1.5 Pa为最佳电离气压,随约束磁场的增强呈线性增长;有效电子温度随功率和气压的增大而下降,随约束磁场的增强线性降低,电子能量几率函数曲线峰位和高能部分都向低能移动,与有效电子温度变化规律吻合。     

Nonlinear collisional monte carlo simulations for high-temperature SOL plasma

A nonlinear Monte Carlo collisional model is applied to to investigate scrape-off layer (SOL) plasmas with high temperatures. In the proposed SOL modeling, A steady state SOL plasma, which satisfies the particle and energy balances and neutrality constraint, is determined in terms of total particle and heat fluxes across the separatrix, the edge plasma temperature, the secondary electron emission coefficient, and the SOL size. A conductive heat flux into the SOL is effectively modeled via random exchange of source particles and the SOL plasma particles. It is found that the potential drop and the electron transmission factor in the collisional SOL plasma are in good agreement with the theoretical prediction. The cooling effect of secondary electrons in the high temperature divertor operation is investigated. In such a collisionless plasma, the present nonlinear collision model is useful because the electron distribution function deviates far from a Maxwellian distribution. In the presence of strong secondary electron emission, the electron sheath energy transmission factor in the collisionless regime is found to be significantly smaller than that in the collisional regime. This fact suggests that a high-temperature divertor operation can be possible.     

甚高频激发容性耦合氩等离子体的电子能量分布函数的演变

甚高频激发的容性耦合等离子体由于离子通量和能量的相对独立可控而受到人们的关注. 本文采用朗缪尔探针诊断技术测量了40.68 MHz激发的容性耦合Ar等离子体的特性(如电子能量概率分布、电子温度和密度等)随宏观参量的演变情况. 实验结果表明, 电子能量概率分布随着气压的增加从双麦克斯韦分布逐步转变为单麦克斯韦分布并最终演变为Druyvesteyn分布, 而射频激发功率的增加促进了低能电子布居数的增强; 在从等离子体放电中心移向边界的过程中, 低能电子的布居数显著下降, 而高能电子的布居则有所上升; 放电极板间距的变化直接导致了等离子体中电子加热模式的转变. 另外, 我们也对等离子体中的高低能电子密度和温度的分配情况进行了讨论.     

Effect of neutral pressure on the He plasma flow measurement in a linear device

Axial and azimuthal flow velocities have been measured in a linear plasma device called NAGDIS-II (NAGoya DIvertor Simulator-II), along with plasma density and electron temperature, using a vector Mach probe composed of two Mach probes, one of which is for the axial flow, and the other is for the azimuthal flow. To study the effect of neutral pressure on the deduction of the Mach numbers, the ratio of upstream to downstream currents are measured by changing the neutral pressure for the deduction of flow velocities. Helium plasma was generated with pressure of 2–35 mTorr. Since the ion gyro-radius at the magnetic flux of 300 G is larger than the probe size, an unmagnetized collisionless Mach probe theory was used for the deduction of Mach numbers and their variations. In order to check the range of collisionality, plasma density (n_e = 10¹⁰–10¹¹ cm^?3) and electron temperature (T_e = 2–9 eV) are measured by a single electric probe using a conventional collisionless probe theory. Variations of Mach number, electron temperature and plasma density with collisionless models are to be compared with those using collisional models for different pressures where ionization and ion-neutral collision are included. Mach numbers by the collisionless model are found to be overestimated by 120% for the maximum difference even in weakly collisional plasmas. A clear flow reversal exists in the axial direction with higher pressure plasma, even in the linear machine. Azimuthal flows are also measured simultaneously along with axial flows, yet they seem to be very small in the present cold ion plasma (T_i/T_e << 1).     

Complete spectrum of kinetic eigenmodes for plasma oscillations in a weakly collisional plasma

Kinetic eigenmodes of plasma oscillations in a weakly collisional plasma, described by a collision operator of the Fokker-Planck type, are obtained in closed form for initial-value as well as for boundary-value problems. These eigenmodes, which are smooth and compose a complete discrete spectrum, play the same role for weakly collisional plasmas as the Case-Van Kampen modes do for collisionless plasmas.     

A contribution to the assessment of the influence of collisions on the measurements with Langmuir probes in the thick sheath working regime

In the present work we investigate theoretically and experimentally the influence of elastic collisions in a probe sheath on a cylindrical Langmuir probe. The analysed probe working regime covers conditions under which the following probe characteristic parameters are comparable: the probe radius, the Debye length and both the ion and electron mean free paths.The preliminary investigations under almost collisionless conditions show good agreement between theoretical and experimental values of the ion saturation currents and of the floating potentials only when the ion currents for the studied working regime of the cylindrical Langmuir probe are calculated according to the theory of Chen (Plasma Phys.7 (1965)47). These collisionless currents form the basis for the calculation of the collision-corrected probe characteristics according to the presented procedure by Talbot and Chou (Rarefied Gas Dynamics, Academic Press, New York, 1966, p. 1723).The applied theoretical analysis covers the influence of the collisions on the electron and ion current of the single probe characteristic and on the estimation of the space potential. The results of the calculations are presented in graphical overviews for the series of cases of practical importance. The other working regimes can be covered using the calculating procedure presented.For comparison of the calculated collision-corrected characteristics with those from an experiment we used the positive column plasma of the He glow discharge where the electron density is known and the space potential can be experimentally estimated from the lowest excitation potential of He. The comparison was carried out for the ion and electron currents, the floating potential and the zero-cross of the probe characteristic second derivative.The estimation of the secondary electron current contribution to the total probe current shows that it limits the applicability of the collision-corrected probe characteristic to the plasma diagnostic in the transition to the collision-determined working regime.     

Langmuir Probe Determination of Charged Particles Density in an rf Discharge

The article presents results of probe measurements of the electron and ion densities in an argon rf discharge. The electron density is determined from the electron probe current at the space potential which is estimated by extrapolation of the linear part of the probe electron current dependence to the plasma potential. The plasma potential is calculated from the floating potential. The positive ion density is determined from the probe ion saturated current according to collisional KOPICZYNSKI and ZAKREWSKI model [1]. The agreement between the electron and ion densities is better than in the work of HOPKINS and GRAHAM [2], where the collisionless Lafram-boise theory is used under similar conditions.     

3D combinational curves for accuracy and performance analysis of positive biometrics identification

The receiver operating characteristic (ROC) curve has been widely used as an evaluation criterion to measure the accuracy of biometrics system. Unfortunately, such an ROC curve provides no indication of the optimum threshold and cost function. In this paper, two kinds of 3D combinational curves are proposed: the 3D combinational accuracy curve and the 3D combinational performance curve. The 3D combinational accuracy curve gives a balanced view of the relationships among FAR (false alarm rate), FRR (false rejection rate), threshold t, and Cost. Six 2D curves can be derived from the 3D combinational accuracy curve: the conventional 2D ROC curve, 2D curve of (FRR, t), 2D curve of (FAR, t), 2D curve of (FRR, Cost), 2D curve of (FAR, Cost), and 2D curve of (t, Cost). The 3D combinational performance curve can be derived from the 3D combinational accuracy curve which can give a balanced view among Security, Convenience, threshold t, and Cost. The advantages of using the proposed 3D combinational curves are demonstrated by iris recognition systems where the experimental results show that the proposed 3D combinational curves can provide more comprehensive information of the system accuracy and performance.     

Thomson scattering off a pair （electron-positron） plasma

Thomson scattering off a pair (electron--positron) plasma is theoretically investigated in the collisionless and collisional limits respectively. Our calculations show that the power spectrum of the Thomson scattering off a collisionless pair plasma is just proportional to the velocity distribution function of the particles in the plasma. Collective modes in the plasma do not have any effects on the Thomson scattering spectrum because of the correlation between the negatively- and positively-charged particles. In the collisional limit, the power spectrum of the Thomson scattering presents three spikes: two peaks correspond to two contra-propagating sound waves and one peak corresponds to an entropy wave.     

Langmuir单探针诊断射频辉光放电等离子体及其数据处理

Langmuir探针是诊断等离子体参数的重要手段.报道了在氩气射顿(13.56MHz)辉光放电等离子体中使用调谐单探针进行诊断,对探针I-V特性曲线的统计噪声进行了数字滤波的光滑化处理,而后求二次微商.在相同的放电条件下,使用自行设计的微分电路,对探针特性二次微商进行在线测量.这两种方法得到的二次微商结果能够较好地符合. 关键词： Langmuir探针 二次微商 数值滤波 微分电路     

Infrared wave interaction with an electron in the rectangular and circular plasma waveguide

In this article, the effect of the electron collision frequency with background ions on TM mode field components, the trajectory, and the electron energy gain in interaction infrared radiation with collisional plasma is studied. The field components of the TM mode in the rectangular and circular collisional plasma waveguides are obtained. The deflection angle and acceleration gradient of an electron in the fields associated with a transverse magnetic (TM) wave propagating inside a plasma waveguide for TM mode is studied. The relativistic momentum and energy equations for an electron are solved, which was injected initially along the propagation direction of the infrared. The results for collisionless and collisional plasma are graphically represented. Finally, the results for rectangular and circular waveguides are compared.