Possibility of rarefaction shocks in anisotropic plasma

The density variation in low-intensity shock waves propagated in an anisotropic rarefied plasma is studied on the basis of a system of relations in the Chew-Goldberger-Low magnetohydrodynamics (CGL MHD) approximation [1].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 161–164, July–August, 1989.The author is grateful to G. A. Lyubimov, A. G. Kulikovskii, A. A. Barmin, and I. S. Shishkin for discussing the results.     

Long time evolution of collisionless shocks in laser produced counterstreaming plasmas

Long time evolution of collisionless shocks in laser-produced plasmas is discussed. By irradiating a double plane target a high Mach number collisionless shock has been observed in laser produced counterstreaming plasmas [Kuramitsu et al., Phys. Rev. Lett., 106, 175002 (2011)]. While in early time we observe the shock in front of one plane, which is irradiated with the laser, we observe another shock in front of the other plane in much later time than the first shock formation. These two shocks coexist and collide or merge with each other as time passes. This means that the upstream plasmas for the first and second shocks have to be provided from the second and first shock sides, respectively, i.e., both the first and second shock have to be collisionless. There are two major candidates to account for the long time evolution of the collisionless shocks. One is that the secondary plasmas at the planes can be continuously created by the plasmas from the other planes. Another is that the actual shock thickness is much thiner than the detection limit, as indicated by numerical simulations.     

Studies on the dynamic buckling of circular plate irradiated by laser beam

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Time-resolved temperature field of monocrystalline silicon irradiated by a millisecond pulse laser

Based on the thermal conduction equation that takes into account phase changes and the evolution of thermophysical parameters with temperature, laser-induced heating and melting of monocrystalline silicon are studied. The changes in the behavior of silicon temperature at different places within the irradiation spot and at different time instants are investigated by the finite element and finite difference methods for a wide range of energy and duration of millisecond laser pulses with the Gaussian spatial and temporal shapes. The numerical results are compared with the experimental measurements.     

Influence of shear layers on the structure of shocks formed by rectangular and parabolic blockages placed in a subsonic flow-field

Flow blockages are used to promote the transition of a flame to a detonation. The structure of shock waves formed with different configurations of blockages was experimentally determined for subsonic incoming flow. High speed subsonic flows could develop ahead of a turbulent flame and the interaction of such flows with blockages could lead to the formation of interacting shock waves, slipstreams, and expansion waves. A blow-down test setup was designed to study the interacting shock pattern formed with different configurations of blockages. The flow was found to accelerate to low supersonic velocities during its passage over the blockages. The shock structure downstream of the blockages was found to depend on the shape, size, and number of blockages as well as the spacing between them. While a parabolic-shaped blockage provided shocks of maximum strength, large blockage ratio values did not permit the formation of shocks. The shear layer, formed in the flow downstream of the blockages, reflected the expansion fan as shock waves and was found to be a major feature influencing the formation of the interacting structure of oblique shocks. The structure and strength of the shock waves are analyzed using hodograms. The formation of the interacting family of shock waves using different configurations of blockages and the spacings between them are discussed.     

飞秒激光辐照铝材料的分子动力学数值模拟

采用大尺度分子动力学方法对飞秒激光辐照金属铝材料的效应进行了数值模拟。利用分子动力学方法给出了飞秒激光辐照后,材料表面发生熔化和喷溅,冷凝后形成一层很薄的多孔介质的物理图像,及产生的应力波传播过程等。数值模拟结果表明分子动力学方法可以用于飞秒激光对材料辐照效应的研究。     

弹性带形域中多个半圆柱形凹陷对SH波的散射

对稳态SH（shear horizontal）导波在表面含有多个半圆柱形凹陷的弹性带形介质内的散射问题进行了研究,并给出了解析解。首先,运用导波展开法构造平面SH导波;然后,利用累次镜像法构造出满足带形域上、下两条直边界应力自由条件的散射波;最后,根据凹陷边沿的切应力为零的条件得到定解方程。通过算例分析了累次镜像法的精度、凹陷边沿的动应力集中和上、下边界位移幅值的变化情况。数值结果表明：只有一个凹陷时,中高频率的入射波和小厚度的带形域会引起凹陷边沿更高的动应力集中,上边界位移幅值的最大值会出现在凹陷的迎波面附近;当有两个凹陷时,大多数情况下,第二个凹陷对第一个凹陷边沿的动应力集中起放大作用,并且在理想弹性带形介质内,两凹陷之间的影响在相距无穷远时也会存在。

     

Nonlinear dynamical magnetosonic wave interactions and collisions in magnetized plasma

The one-dimensional nonlinear dynamical wave interactions in a system of quasineutral two-fluid plasma in a constant magnetic field are investigated.The existence of the travelling wave solutions is discussed.The modulation stability of linear waves and the modulation instability of weakly nonlinear waves are presented.Both suggest that the Korteweg-de Vries(KdV) system is modulationally stable.Besides,the wave interactions including the periodic wave interaction and the solitary wave interactio...     

Plasma emission spectroscopy of solids irradiated by intense XUV pulses from a free electron laser

The FLASH XUV-free electron laser has been used to irradiate solid samples at intensities of the order 10¹⁶ W cm^?2 at a wavelength of 13.5 nm. The subsequent time integrated XUV emission was observed with a grating spectrometer. The electron temperature inferred from plasma line ratios was in the range 5–8 eV with electron density in the range 10²¹–10²² cm^?3. These results are consistent with the saturation of absorption through bleaching of the L-edge by intense photo-absorption reported in an earlier publication.     

激光辐照下多层圆柱体中三维瞬态温度场的解析解

考虑外表面的气流影响和层间温度与传热的协调关系,建立了激光辐照下,层合圆柱体中的三维瞬态热传导解析模型。利用特征值法和Bessel函数,导出了各层柱体中三维瞬态温度场的封闭解析解。以一维轴对称问题为例计算了柱体中的瞬态温度场,给出了柱体内部温度随时间的变化和柱体表面换热系数对温度场的影响规律。本文的理论解可进一步用于分析层合圆柱体中的三维瞬态热-力效应,并可作为相应问题的数值模拟中数值模型的修正依据。     

Accelerating piston action and plasma heating in high-energy density laser plasma interactions

In the field of high-energy density physics (HEDP), lasers in both the nanosecond and picosecond regimes can drive conditions in the laboratory relevant to a broad range of astrophysical phenomena, including gamma-ray burst afterglows and supernova remnants. In the short-pulse regime, the strong light pressure (>Gbar) associated ultraintense lasers of intensity I > 10¹⁸ W/cm² plays a central role in many HEDP applications. Yet, the behavior of this nonlinear pressure mechanism is not well-understood at late time in the laser–plasma interaction. In this paper, a more realistic treatment of the laser pressure ‘hole boring’ process is developed through analytical modeling and particle-in-cell simulations. A simple Liouville code capturing the phase space evolution of ponderomotively-driven ions is employed to distill effects related to plasma heating and ion bulk acceleration. Taking into account these effects, our results show that the evolution of the laser-target system encompasses ponderomotive expansion, equipartition, and quasi-isothermal expansion epochs. These results have implications for light piston-driven ion acceleration scenarios, and astrophysical applications where the efficiencies of converting incident Poynting flux into bulk plasma flow and plasma heat are key unknown parameters.     

激光冲击强化过程中蒸气等离子体压力计算的耦合模型

首先基于系统能量守恒条件,提出了一种计算蒸气等离子体压力的一维耦合计算模型。模型中不仅考虑了蒸气等离子体界面压力与质点速度的非线性效应,同时也考虑了界面烧蚀所致的运动速度,将蒸气等离子体的膨胀与约束介质的变形耦合。在耦合模型的基础上,采用显式差分计算程序与显式有限元计算程序LS-DYNA互相迭代求解的方法,对不同激光功率密度分布下的蒸气等离子体压力进行了计算。结果表明,计算结果与实验测量结果具有很好的一致性,证明了计算模型的合理性。