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首页> 外文会议>International Conference on Atomic Processes in Plasmas >Spectroscopic Investigation of the Particle Density and Motion in an Imploding z-Pinch Plasma
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Spectroscopic Investigation of the Particle Density and Motion in an Imploding z-Pinch Plasma

机译：浅析Z夹夹等离子体中颗粒密度和运动的光谱研究

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Experimental investigations of the ion density and flow as a function of time and space in z-pinch plasmas are of key importance for improving the understanding of z-pinch dynamics. For such studies, measurements of emission-line shapes can be highly useful.In the present experiment line emission of oxygen ions is used to investigate the ion density and motion in the imploding plasma in a 0.6-μs, 220-kA z-pinch experiment. For the time period studied here (220 – 85 ns before the stagnation on-axis), the plasma properties have been extensively characterized previously, employing various spectroscopic methods to determine the time-dependent radial distributions of the ion velocities, the magnetic field, the charge-state composition, the electron temperature, and the particle densities. In particular, the electron density was determined from the absolute intensities of spectral lines, from the ionization times in the plasma, and from momentum-balance considerations, based on the previously measured time-dependent magnetic field radial distribution. The electron density determined was also found to be consistent with energy-balance considerations, as described in Ref. [10].Using the values of the electron density and temperature as a function of the radial coordinate and time, the Stark widths of all emission lines observed (of O II – O VI) were calculated (we note that all lines used are isolated, i.e, their Stark shapes are Lorentzian). For the Stark broadening computations we employed two independent methods, namely, a quantum-mechanical method based on the Baranger formula and a non-perturbative semi-classical method. For the quantum-mechanical calculations of the line widths performed, we use electron-collision cross sections calculated using two approaches: the Coulomb-Born-Exchange method and the convergent close-coupling (CCC) method. The latter has been successfully applied to many atomic-collision experiments, for example for the analysis of spectral-line broadenings in Li- and Be-like ions. The calculation results of the quantum-mechanical and of the semi-classical methods were found to be similar for the purpose of present discussion.The total widths predicted for each line were then determined by convolving the calculated Stark widths with the Doppler broadening (assuming equal ion and electron temperatures; i.e., Ti= Te) and with the measured instrumental broadening. It was found that these widths are significantly smaller than the observed widths. For example for the 3144.7-? line of OV, the calculated Stark width is found to be 0.20 ± 0.08 ?, the Doppler broadening (due to Ti = Te = 13 eV) is 0.42 ± 0.09 ?, and the instrumental broadening is 0.21 ?. The width resulting form the convolution of these three contributions is 0.51±0.13?. This value is much smaller than the observed width, 0.98 ± 0.03 ?. Similar results were obtained for the other O III – O VI lines.Since the uncertainties in the Stark-broadening calculations are believed to be significantly smaller than the difference between the computed and experimental line widths, an additional Doppler broadening is suggested. Energy balance considerations, based on the radial distributions of the electron temperature, electron density, charge state, and magnetic field previously determined (Refs. [8-11]) allow for demonstrating that an ion temperature much higher than Te is unlikely. For explaining the extra broadening we thus suggest the presence of turbulent ion motion at the outer plasma boundary, which develops in the plasma during the implosion. The spatial scale of the turbulence is believed to be smaller than the spatial resolution of the measurements, which is 0.5 mm.Based on this explanation, it is inferred that the ion kinetic energy associated with the turbulence can be up to 70% of the radially-directed kinetic energy. It should be emphasized that these non-thermal ion velocities are inferred for the imploding plasma that was observed to be with no geo
机译：离子密度的实验研究和流量为在Z箍缩等离子体的时间和空间的函数是至关重要的改善Z箍缩动力学的理解。对于这种研究，发射线的形状的测量可以是高度useful.In氧离子的本实验线发射用于研究内爆等离子体中的离子密度和运动在一个0.6微秒，220-KA z箍缩实验。对于这里所研究的时间段（220 - 轴上停滞前85纳秒），等离子体性质已经被广泛先前表征，采用各种光谱方法来确定离子速度的依赖于时间的半径方向的分布，磁场，该电荷状态的组合物，电子温度，和颗粒密度。特别是，电子密度从谱线绝对强度确定，从等离子体中的离子化时间，并从动量平衡的考虑，基于先前测量的随时间变化的磁场的径向分布。确定的电子密度也被发现与能量平衡方面的考虑相一致，如在参考文献中描述。 [10]。采用的电子密度和温度的值作为的函数径向坐标和时间，所有发射线的宽度斯塔克观察（的O- II - ØVI）进行了计算（我们注意到，使用的所有行被分离，即它们的斯塔克形状洛伦兹）。对于斯塔克加宽计算我们采用两种独立的方法，即，基于所述Baranger式和非微扰半经典方法的量子力学方法。对于线宽的量子力学的计算执行中，我们使用通过两种方法来计算电子碰撞截面：库仑出生交换法和收敛紧密耦合（CCC）方法。后者已被成功地应用于许多原子碰撞实验，例如用于谱线加宽的在俪分析和Be状离子。量子力学的和的半经典方法的计算结果被发现是用于预测对每一行本discussion.The总宽度的目的相似然后通过用多普勒加宽卷积计算斯塔克宽度（假定等于确定离子和电子温度，即TI = Te）的并与所测量的仪器增宽。结果发现，这些宽度比观测到的宽度显著小。例如，对于3144.7-？宽度被发现是0.20±0.08 OV，所计算出的斯塔克线？，多普勒加宽（由于TI =碲= 13电子伏特）是0.42±0.09？，并且仪器增宽为0.21？。所得形式这三种贡献的卷积的宽度是0.51±0.13？该值比所观察到的宽度小得多，0.98±0.03？。类似的结果对其它øIII得到 - ØVI lines.Since在斯塔克加宽计算中的不确定性被认为是比所计算的和实验线宽之间的差较小的显著，附加多普勒加宽被建议。能量平衡方面的考虑的基础上，电子温度，电子密度，电荷状态和磁场的径向分布先前确定的（参考文献[8-11]）允许证明离子温度除Te高得多的可能性不大。用于说明额外加宽我们因此建议湍流离子运动的在外部等离子体边界的存在，其中所述内爆期间发展的等离子体英寸湍流的空间尺度被认为是比测量的空间分辨率，这是0.5 mm.Based在此说明时，可以推测与紊流有关的离子的动能可高达的径向70％ -directed动能。应当强调的是，这些非热离子速度被推断为被观察到与没有所述地理区域内爆等离子体

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