Z箍缩驱动器与丝阵负载耦合特性研究

以丝阵内爆零维模型为基础,采用Pspice模拟行为建模方法,建立了丝阵内爆动态电感与Z箍缩驱动器耦合的全电路模型,实现驱动器放电过程与丝阵内爆过程的自洽求解,并研究了丝阵参数、电路参数对内爆过程的影响.结果表明:丝阵负载与驱动器存在强耦合关系,丝阵参数、电路参数对丝阵峰值箍缩电流、内爆时间、内爆动能影响很大;在驱动器参数不变,内爆时间不超过电路固有放电周期1/4的前提下,峰值箍缩电流、内爆时间、内爆动能随丝阵质量的增加而增大,内爆时间随丝阵初始半径的增加而增大;在丝阵参数不变时,随着驱动器等效电容的增大,内爆时间减小,丝阵内爆动能增大,但驱动器储能转化为内爆动能的效率却先增大后减小.对于特定的驱动器,优化的丝阵参数应使内爆过程充分利用驱动器固有放电周期的上升沿,使丝阵快速收缩的时间起点接近电路固有放电周期的四分之一,以获得最大的动能效率. 关键词： Z箍缩驱动器 零维内爆模型 模拟行为建模 耦合特性     

准球形电磁内爆动力学研究及能量定标关系浅析

通过改变Z箍缩负载的初始形状和/或质量密度分布,可以实现等离子体的准球形聚心内爆.同柱形箍缩相比,准球形电磁内爆可以将内爆动能集中加载至负载中心较小的空间区域内,获得更高的能量密度,从而在驱动Z箍缩动态黑腔实现聚变点火方面具有潜在优势.准球形电磁内爆的负载和电极结构比柱形Z箍缩更复杂,球面收缩的几何特点使其内爆动力学过程和能量定标关系显著区别于柱形内爆.本文利用解析的薄壳模型推导并分析了理想条件下准球形电磁内爆的动力学行为和能量定标关系,并同二维磁流体力学模拟结果进行了比较.与柱形Z箍缩内爆相比,准球形电磁内爆的动能不仅与驱动电流有关,而且敏感地依赖于负载的初始尺寸.在不显著降低驱动电流和内爆品质的前提下,适当增加负载的初始半径和最大纬度,有利于获得更多的内爆动能和能量加载密度.     

内爆靶丸X射线轫致辐射谱的重建方法及应用北大核心CSCD

提出了一种对内爆靶丸X射线轫致谱重建的方法。该方法的目的是通过重建内爆靶丸的轫致辐射谱,得到内爆靶丸有价值的信息。这种方法将轫致谱能段分为五个部分,假设每个部分的平均能量强度相等,用一种包含了五个不同滤片组的多能段针孔相机对同一个内爆靶丸进行成像,并且用IP板进行接收。五组不同的像可以给出五个不同的线形方程组,这样就可以还原出轫致辐射谱。使用该方法还原了在神光Ⅲ原型装置上内爆靶丸的轫致辐射谱,并据此给出了内爆热斑的温度,所得的结果与用示踪元素特征谱线给出的温度符合得较好,证实该方法和结果是可靠的。     

Z箍缩等离子体内爆实验金属丝阵负载优化设计分析

金属丝阵Z箍缩(Z-pinch)内爆是产生强x射线辐射的重要方法之一.在一定脉冲功率加速器条件下，金属丝阵质量和丝阵半径的选择决定了Z-pinch内爆等离子体辐射产额的大小.采用薄壳模型计算了不同丝阵质量、不同丝阵半径、不同粗细和不同材料金属丝构成的丝阵的内爆时间、内爆轨迹、内爆速度，以及最大动能和动能转换率，综合分析了丝间隙、内爆时间、动能转换率与丝阵质量和丝阵半径的关系，给出了在一定负载驱动电流条件下，金属丝阵的最佳参数.分析表明计算结果与实验上观察得到的内爆规律一致. 关键词： Z-pinch内爆等离子体 金属丝阵负载 薄壳模型     

内爆靶丸X射线轫致辐射谱的重建方法及应用

提出了一种对内爆靶丸X射线轫致谱重建的方法。该方法的目的是通过重建内爆靶丸的轫致辐射谱,得到内爆靶丸有价值的信息。这种方法将轫致谱能段分为五个部分,假设每个部分的平均能量强度相等,用一种包含了五个不同滤片组的多能段针孔相机对同一个内爆靶丸进行成像,并且用IP板进行接收。五组不同的像可以给出五个不同的线形方程组,这样就可以还原出轫致辐射谱。使用该方法还原了在神光Ⅲ原型装置上内爆靶丸的轫致辐射谱,并据此给出了内爆热斑的温度,所得的结果与用示踪元素特征谱线给出的温度符合得较好,证实该方法和结果是可靠的。     

神光Ⅱ装置靶丸内爆过程X射线背光照相实验研究

在神光Ⅱ装置上,8路激光注入金柱腔靶产生X射线驱动位于柱腔中心的DD靶丸内爆,第9路激光辐照Pd背光靶产生的L线X射线透视内爆靶丸,用针孔成像方式获得靶丸的透视图像,高速X射线条纹相机记录靶丸透视图像,建立了间接驱动内爆靶丸背光照相的实验方法,清晰地观测到了靶丸内爆的过程,对透视图像分析获得了内爆靶丸壳层运动轨迹和速度的实验数据,所获实验结果可用于间接驱动靶丸优化设计,还可用于内爆动力学数值模拟建模和计算结果的验证。     

神光Ⅱ装置靶丸内爆过程X射线背光照相实验研究北大核心CSCD

在神光Ⅱ装置上,8路激光注入金柱腔靶产生X射线驱动位于柱腔中心的DD靶丸内爆,第9路激光辐照Pd背光靶产生的L线X射线透视内爆靶丸,用针孔成像方式获得靶丸的透视图像,高速X射线条纹相机记录靶丸透视图像,建立了间接驱动内爆靶丸背光照相的实验方法,清晰地观测到了靶丸内爆的过程,对透视图像分析获得了内爆靶丸壳层运动轨迹和速度的实验数据,所获实验结果可用于间接驱动靶丸优化设计,还可用于内爆动力学数值模拟建模和计算结果的验证。     

“强光一号”锥形丝阵内爆特性研究

在强光一号装置开展小倾角单层锥形钨丝阵实验, 获得了锥形丝阵在消融阶段, 拉链内爆阶段和滞止阶段的辐射参数和辐射图像. 消融阶段的物理图像映证了使用火箭模型对锥形丝阵消融过程及先驱等离子体形成的分析. 结合分幅像、针孔像和条纹像, 解释了锥形丝阵在内爆箍缩阶段阴极部分首先发生内爆并产生硬X射线成分的原因. 观察到的锥形丝阵的拉链内爆速度达到2.59× 10⁷ cm/s, 拉链内爆及滞止的持续时间达到40 ns, 远大于相近尺寸的柱形丝阵. 通过特殊构型丝阵内爆特性的研究, 为进一步验证基于柱形丝阵建立的Z-pinch理论模型, 完善MHD模型的普适性提供必要的实验数据.     

神光Ⅱ与神光Ⅲ原型上的辐射驱动小收缩比内爆靶设计

本文建立辐射驱动小收缩比(5至10倍)的内爆靶丸的设计方法,并利用辐射流体力学程序Multi-1d对神光Ⅱ和神光Ⅲ原型装置的辐射驱动小收缩比内爆靶丸进行模拟计算,设计出小收缩比内爆靶丸的构形,计算结果给出压缩比、中子产额、压缩面密度随燃料压力变化等内爆物理参量.神光Ⅱ装置上的内爆靶燃料分别采用DD气体和DT气体两种;神光Ⅲ原型装置的内爆靶燃料采用DD气体.神光Ⅱ上小收缩比内爆实验结果与模拟结果基本一致,表明Multi-1d用于设计此类实验的可靠性. 关键词： 辐射驱动 小收缩比 内爆 面密度     

辐射驱动内爆流线实验测量

内爆速度的测量是惯性约束聚变研究中的核心问题, 是判断聚变点火反应的关键物理量. 在神光II激光装置上, 利用KB显微镜配合时间分辨为10 ps的条纹相机, 对1600 J激光能量注入, 3倍频, 脉宽为1 ns黑腔辐射驱动CH靶球, 获得了清晰的辐射驱动内爆流线轨迹X射线图像. 通过流线轨迹图像给出了最大内爆速度为160 km/s. 利用Multi1D程序对内爆压缩流线和壳层速度变化进行了模拟, 实验数据和理论模拟较符合.     

二维三温能量方程的九点差分格式及其迭代解法

给出了激光驱动内爆数值模拟中二维三温能量方程的九点差分格式及其迭代解法,并给出了九点差分格式与五点差分格式对比计算结果,对一维和二维物理模型进行了数值模拟,得到了令人满意的数值结果。     

An exact solution to the relativistic equation of motion of acharged particle driven by a linearly polarized electromagneticwave

An exact analytic solution is found for a basic electromagnetic wave-charged particle interaction by solving the nonlinear equations of motion. The particle position, velocity, and corresponding time are found to be explicit functions of the total phase of the wave. Particle position and velocity are thus implicit functions of time. Applications include describing the motion of a free electron driven by an intense laser beam     

Theoretical study of armchair single-walled carbon nanotubes in the presence of a strong laser field: high harmonic generation

The nonlinear optical response of armchair single-walled carbon nanotubes under high-intensity laser irradiation is investigated theoretically and numerically because the generation of high harmonics requires a strong laser field and come from the nonlinear motion of π electrons in carbon nanotubes. A nonperturbative approach is performed to investigate the effect of group velocity on the high harmonics spectrum by nanotubes. A set of the quantum kinetic equations is derived, which includes coupled equations for the density matrix. By solving the density matrix and the current density equations numerically, we have studied the high-order harmonic generation from metallic carbon nanotubes driven by an electromagnetic external field.     

Fast self-pulsing through nonlinear incoherent feedback

We consider a double-pass ring cavity with nonlinear incoherent optical feedback and analyze its response when it is driven by a continuous laser beam. This particular cavity is equivalent, in the temporal domain, to a simple spatial-pattern-generating system made from a Kerr slice and a feedback mirror. After formulating the evolution equations, we investigate the behavior of small-amplitude solutions and obtain an expression for the round-trip gains. We then explore the important effect of dispersion in the nonlinear medium. Finally, we show that stable modes are possible by solving numerically the full nonlinear equations.     

Field-driven super/subradiant lasing without inversion in three-level ladder scheme

A model of a superradiant laser comprising of N three-level systems driven by two pumping lasers is considered in semiclassical approximation. Steady-state equations for density matrix elements are solved both analytically and numerically. Various properties of generated light are investigated. It is found that such a laser can exhibit both superradiance, when the intensity scales as N(2), and subradiance when the intensity does not depend on N. The phase of the laser field is locked to the relative phase of the pumping lasers.     

Broadband Terahertz Wave Generation from Monolayer Graphene Driven by Few-Cycle Laser Pulse

We theoretically investigate the characteristics of terahertz(THz) radiation from monolayer graphene exposed to normal incident few-cycle laser pulses, by numerically solving the extended semiconductor Bloch equations. Our simulations show that the THz spectra in low frequency regions are highly dependent on the carrier envelope phase(CEP) of driving laser pulses. Using an optimal CEP of few-cycle laser pulses, we can obtain broadband strong THz waves, due to the symmetry breaking of the laser-graphene system. Our results also show that the strength of the THz spectra depend on both the intensity and central wavelength of the laser pulses. The intensity dependence of the THz wave can be described by the excitation rate of graphene, while wavelength dependence can be traced back to the band velocity and the population of graphene. We find that a near single-cycle THz pulse can be obtained from graphene driven by a mid-infrared laser pulse.     

双色反向旋转圆偏振激光场下氩原子高次谐波的产生

通过二阶分裂算符法数值求解了二维含时薛定谔方程,研究了双色反向旋转圆偏振激光场作用下氩原子的高次谐波的产生.研究表明,双色反向旋转圆偏振激光场的幅值比对高次谐波发射的效率有较大影响,当幅值比为1.4时高次谐波的发射效率最高,并应用时频分析方法、经典三步模型以及利萨茹图形等解释了高次谐波发射的物理机制.研究了不同幅值比情况下谐波场的旋转偏振特性,发现对不同频段的谐波谱的电场进行叠加,谐波场的偏振特性随幅值比的不同而发生变化,但谐波场的旋向性与入射激光脉冲的旋向性相同,不受幅值比变化的影响.     

Dynamics of cooperative emissions in a cascade three-level molecular system driven by an ultrashort laser pulse

This paper investigates the dynamics of cooperative emissions in a cascade three-level system driven by an ultra, short laser pulse by solving numerically the full-wave Maxwell-Bloch equations. The 4, 4＇-bis（dimethylamino） stilbene molecule is used as the model molecule because of its strong two-photon absorption property. The two-colour cooperative emissions are studied as functions of molecular number density and dephasing rate of the dipole coherence. The propagation effects on the evolution of the cooperative radiations are also taken into account. The cooperative radiations are enhanced for large number density of the molecule, while the fast dephasing of the dipole coherence reduces the intensity of the cooperative radiations and delays the emission times or even inhibits the formation of the emissions. The delay time of the radiation decreases with the increase of the molecular number density and the propagation distance.     

Bifurcation and Relaxation Oscillations in Divertor Plasmas

This paper presents a contribution to bifurcation phenomena in scrape-off layer modelling. The bifurcations are caused by the non-monotonic temperature behaviour of the radiation characteristics of plasma impurities. Low-frequency relaxation oscillations observed in divertor plasmas of the ASDEX Upgrade tokamak are analyzed and computed using a simple model for the dynamics of the impurity density and the electron temperature. The corresponding model equations are a special case of a general system of transport equations whose stability is analyzed. Bifurcations are calculated by solving autonomous and parametrically driven model equations.     

短脉冲驱动下膨胀冷却等离子体中软X射线激光研究

在解析求解等离子体流体力学方程组的基础上，数值求解了以ＭｇＸＩ为主体的等离子体能级占据数速率方程，进而给出了短脉冲驱动下膨胀冷却等离子体中ＭｇＸＩｌｓ３ｄ－ｌｓ４ｆ激光跃迁增益系数的时空分布，讨论了泵浦激光脉冲宽度对增益的影响。 关键词：