Formation of cavities in a Z pinch plasma

Technical Physics - The spatial structure and dynamics of the plasma in a high current vacuum spark discharge are studied via pulsed shadowgraphy. The formation of cavities in the neck plasma at...     

Z箍缩内爆产生的电磁脉冲辐射

讨论了Z箍缩内爆产生的低频电磁脉冲的辐射特性. Z箍缩驱动金属丝阵或固体套筒高速内爆,部分磁能通过与负载的运动耦合而向外辐射. 理论结果表明,电磁脉冲辐射功率由电流和内爆轨迹共同决定. 在中国工程物理研究院流体物理研究所的初级实验平台上开展了负载电流为7 MA,10%–90%上升时间65 ns的丝阵Z箍缩实验,根据实验测得的电流和内爆轨迹得到了电磁脉冲的辐射功率和频谱. 电磁脉冲峰值功率约为1 GW,能量约为0.5 J,能量转换效率约为10^-7;峰值频率位于20–70 MHz,具有较宽的辐射频谱. 电磁脉冲辐射参数远小于软X射线辐射参数（峰值功率为50 TW,能量为0.5 MJ）. 在弱相对论条件下,电磁脉冲辐射功率近似地正比于电流的6次方,随电流急剧增大. 软X射线辐射是丝阵Z箍缩过程中的主要能量转换形式,本文的研究结论表明,在更高的驱动电流下,电磁脉冲辐射将提供另一种重要的能量转换途径,势必会对诊断设备造成严重影响;此外,这类强电磁脉冲在其他领域也具有潜在的应用价值. 关键词： Z箍缩 内爆 电磁脉冲     

Mesic molecules formation in solid deuterium

An explanation is suggested for the fast ddμ formation rate observed in solid deuterium. This revised version was published online in August 2006 with corrections to the Cover Date.     

可见光分幅相机及其在Z箍缩诊断中的应用

研制了一套纳秒级可见光分幅相机,用于"强光一号"早期放电过程的观察和诊断.介绍了相机的主要性能,利用该相机得到了丝阵负载z箍缩等离子体的可见光图像,对结果进行了分析.     

铝丝阵列Z箍缩的辐射磁流体动力学过程

在拉格朗日坐标系下,建立了描述Z箍缩等离子体内爆动力学过程的一维三温辐射磁流体力学方程组,并编制了相应的拉氏程序。利用该程序对美国Sandia实验室Saturn装置上的铝丝阵列内爆实验进行了数值模拟,得到了内爆等离子体各参量的时空分布。其中内爆到心时刻、X光峰值功率、X光总能量等计算结果与实验结果基本一致。表明所建立的物理模型和编制的程序是合理和可靠的。     

预脉冲的抑制及Z-pinch实验可允许的预脉冲电压分析

分析了脉冲功率装置特别是使用Blumlein线装置的预脉冲电压的产生机理,提出了通过一个连接于Marx和地之间的附加电感来平衡充电电路以抑制预脉冲的方法。用Pspice计算的实例表明：使用该方法可以有效地减小预脉冲电压。使用金属丝的比作用量和汽化热两种计算方法分析了Z Pinch实验中丝阵负载可承受的预脉冲电压,计算结果与实验结果对比表明,实验中铝丝的预脉冲电流远大于计算结果的最大值,铝丝发生汽化,验证了计算方法的正确性。     

Two dynamics modes in planar wire array Z pinch implosion

Two dynamics modes,named short ablation mode and long ablation mode,are observed in implosion experiments of planar wire array Z pinch on ’QiangGuang-I’ facility utilizing an optical streak camera.The long ablation mode has a lagged trajectory compared with the short ablation mode.For shot 10035 in a short ablation mode,the initial time of K-shell radiation is consistent with the interaction time for ablation plasma arriving at the centre of wire array,while for shot 10038 in long ablation mode,the initial time of K-shell radiation is about 10 ns earlier.In the two modes,the partial ablation plasma could traverse the wire array plane and then collide in the centre to form a dense plasma column with a diameter of 2.2 mm for shot 10035 and 1.5 mm for shot 10038.     

Measurement of the ionization state and electron temperature of plasma during the ablation stage of a wire-array Z pinch using absorption spectroscopy

Wire-array plasmas were investigated in the nonradiative ablation stage via x-ray absorption spectroscopy. A laser-produced Sm plasma was used to backlight Al wire arrays. The Sm spectrum was simultaneously observed by two spectrometers: one recorded the unattenuated spectrum and the other the transmission spectrum with 1.45-1.55 keV K-shell absorption lines. Analysis of absorption spectra revealed electron temperature in the range of 10-30 eV and the presence of F-, O-, N- and C-like Al ions in the absorbing plasma. A comparison of this electron temperature with the postprocessed absorption spectra of a 2D MHD simulation yields results in general agreement with the data analysis.     

Shock compression of solid deuterium

Experimental data on the compression of solid deuterium at a pressure of ～60 GPa are presented. The data were obtained on a generator of powerful converging spherical shock waves. The results are compared with the data of shock experiments obtained on a Nova laser facility and an electrodynamic EPBF-Z plant.     

喷气Z箍缩内爆等离子体的雪铲模型

在喷气Z pinch内爆等离子体研究中,雪铲模型是一种常用的、比较简单的物理模型。根据实验中提供的电流波形,负载线质量和初始半径,可以通过雪铲模型来估算内爆到心的时刻。根据一维运动方程和不同构形下的解析解以及部分实验结果相结合,讨论了雪铲模型的适用范围。数值计算的内爆时间和实验（Gamble II, Double EAGLE, BLACKJACK 5）测量值符合得较好。结果表明,雪铲模型在喷气Z pinch实验的负载优化设计研究中是很有参考价值的方法。     

Study of the internal structure and small-scale instabilities in the dense Z pinch

High-resolution laser diagnostics at the wavelength of 266 nm were applied for the investigation of Z pinches at the 1-MA generator. The internal structure of the stagnated Z pinches was observed in unprecedented detail. A dense pinch with strong instabilities was seen inside the column of the trailing plasma. Kink instability, disruptions, and micropinches were seen at the peak of the x-ray pulse and later in time. The three-dimensional structure of the stagnated Z pinch depends on the initial wire-array configuration and implosion scenario. Small-scale density perturbations were found in the precursor plasma and in the stagnated Z pinch. Development of instabilities is in agreement with three-dimensional magnetohydrodynamic simulations.     

聚龙一号驱动Z箍缩负载内爆的简化电路模型

为方便描述聚龙一号装置与Z箍缩负载的电磁耦合过程,基于大量电参数实验数据和全电路模拟分析,建立了一个简化的集总电路模型,获得了等效电压波形和等效电阻、电感等集总参量。采用水介质三板输出线出口位置的开路电压作为等效电压,进一步拟合为正弦平方函数,峰值为3.3 MV（当前驱动器充压为65 kV）,零到峰值的时间长度为102.5ns。采用简化的流阻抗模型描述磁绝缘传输线内部空间电子流的电流损失效应。将电路程序与零维负载动力学程序耦合模拟,得到了与实验结果符合的负载电流波形,尤其电流波形的前沿和峰值符合较好,分析了电磁能转化为负载动能的过程。     

Z箍缩动态黑腔负载装配用胶粘剂

由于Z箍缩动态黑腔负载中的低密度聚合物泡沫柱具有多孔结构和极低的力学强度,在装配过程中对胶粘剂有一定的特殊要求。实验以聚氨酯丙烯酸酯为主体树脂,丙烯酸异冰片酯为活性单体,配以光引发剂和偶联剂制得了适用于低密度泡沫粘接用的紫外光固化胶粘剂。测试表明,所研制的胶粘剂的体积收缩率仅为2.25%,且具有较高的固化速率和适当的粘接强度,能够满足稳固、快速装配的要求。通过对粘接界面的观测发现,胶粘剂在诊断孔内没有明显的扩散,且在低密度致密结构泡沫中的扩散厚度较小,均匀性好。     

丝阵负载Z箍缩内爆动力学研究

丝阵负载内爆动力学行为基本可以分为以下四个过程:1)丝的烧蚀;2)壳层的形成;3)内爆;4)滞止.利用所研制的可见光分幅相机和X射线分幅相机在"强光一号"加速器上对多种型号的丝阵负载Z箍缩内爆动力学行为进行了实验研究,获得了从早期单丝烧蚀到等离子体柱崩毁全过程图像,并对实验结果进行了分析,主要研究成果如下:1)发现存在较长时间的丝烧蚀过程,且单丝烧蚀在轴向上并不均匀;实验得到的内爆轨迹与唯像模型计算结果较为一致.2)不论早期的可见光图像还是中后期的软X射线图像都存在明显的阴极发射,内爆后期在阴极附近存在明 关键词： 丝阵 内爆动力学 Z箍缩 脉冲功率技术     

Measurement of instability growth in a magnetized Z pinch in the finite-Larmor-radius regime

The development of the m = 0 instability in a Z pinch was followed and the measured growth rates compared with 2D MHD simulations. Where MHD is valid, the measured growth rates agree well with simulation. Where the ions are magnetized, i.e., where the ion-cyclotron frequency is smaller than the ion-collision frequency and the ratio of the ion Larmor radius to pinch radius is of the order of 0.1, the growth rate was smaller than expected by a factor of 2.5. This is as predicted by finite-Larmor-radius theory. The product of the wave number and the pinch radius was ka approximately 2pi and was the same for all conditions. Perturbations as large as 30% of the pinch radius were observed; no nonlinear saturation was evident.     

Measurements of ultracold-neutron lifetimes in solid deuterium

We present the first measurements of the survival time of ultracold neutrons (UCNs) in solid deuterium (SD2). This critical parameter provides a fundamental limitation to the effectiveness of superthermal UCN sources that utilize solid ortho-deuterium as the source material. These measurements are performed utilizing a SD2 source coupled to a spallation source of neutrons, providing a demonstration of UCN production in this geometry and permitting systematic studies of the influence of thermal up-scatter and contamination with para-deuterium on the UCN survival time.