强激光与等离子体相互作用产生的超强太赫兹辐射

超短强激光脉冲在等离子体中传播时会激发大振幅的等离子体尾波场，它是一种电子等离子体波．由于这是一种静电波，它一般不能转换成电磁辐射．我们发现在不均匀等离子体中激发的尾波场在一定条件下可以通过线性模式转换产生电磁辐射．由于用超短强激光脉冲尾波场可以达到的电场振幅达100GV／m，其振动频率在太赫兹（10^12Hz）附近，用这种方法可以产生电场强度达到GV／m的太赫兹辐射．     

Interpolation formula for the electrical conductivity of nonideal plasmas

On the basis of a quantum‐statistical approach to the electrical conductivity of nonideal plasmas we derive analytical results in the classical low‐density regime, in the degenerate Born limit, and for the contribution of the Debye‐Onsager relaxation effect. These explicit results are used to construct an improved interpolation formula of the electrical conductivity valid in a wide range of temperature and density which allows to compare with available experimental data of nonideal plasmas.     

Phase modulation of intense ultrashort laser pulses reflected from steep, dense plasmas

The phase modulation of intense ( I = 10(18) W/cm(2)) ultrashort laser pulses ( tau(p) = 70 fs) after reflection from steep, dense plasmas has been temporally resolved for the first time in particle-in-cell simulations. The position of the turning point from where the pulse reflects has been compared to the phase modulation, over a range of angles of incidence. At normal incidence or s polarization the phase modulation almost exactly represents the movement of the turning point due to the light pressure. As the angle of incidence is increased for p polarization, the simple Fresnel relationship between phase modulation and displacement of the reflection position, Delta phi(t) = -2k(0)Delta x(t)cos theta(0), increasingly breaks down.     

Single-state measurement of electrical conductivity of warm dense gold

We report on a single-state measurement of electrical conductivity of warm dense gold in the solid to plasma transition regime. This is achieved using the idealized slab plasma approach of isochoric heating of ultrathin samples by a femtosecond laser, coupled with femtosecond probe measurements of reflectivity and transmission. The experiment also reveals the time scale associated with the disassembly of laser heated solid.     

Combined pressure and electrical-resistivity measurements of warm dense aluminum and titanium plasmas

Electrical resistivity, pressure, and internal energy variation of warm dense correlated titanium (density 0.2 g/cm(3)) and aluminum (density 0.1 g/cm(3)) plasmas are measured using a homogeneous and thermally equilibrated media produced inside an isochoric closed-vessel plasma. These data are compared to detailed calculations based on the density functional theory. In the studied temperature range (15,000-30,000 K), it appears that both exchange-correlation and ion-ion interaction treatments are of great importance to calculate accurate theoretical values.     

Comparison of atomic potentials and bremsstrahlung Gaunt factors in dense aluminum plasmas

We determine and compare high temperature high density atomic potentials for dense aluminum plasmas. We then evaluate bremsstrahlung Gaunt factors from these potentials utilizing various methods. The potentials considered are obtained from density functional theory, from the hypernetted chain/Poisson model and from the Thomas-Fermi model. The bremsstrahlung spectra obtained for these three potentials, with the partial wave expansion method and for incident electrons of about 1 keV, are in qualitative agreement. We indicate in which circumstances and with what precision bremsstrahlung Gaunt factors can also be estimated from much simpler potentials, such as the Debye or ion sphere model, and from much simpler calculations of the spectrum, such as the Born-Elwert approximation or a simple classical mechanics approach. The aluminum plasmas considered have temperatures of 0.5-1 keV and electron densities of 10²⁵, 10²⁴, 10²³cm^-3.     

Electron temperatures of intense electron-beam-produced plasmas

A method of estimating the electron temperatures in intense, relativistic, electron-beam-produced plasmas is presented. This method compares spectral line intensities obtained from visible emission spectroscopy to those expected from local thermodynamic equilibrium (LTE) plasmas. The line intensities, particularly those originating from highly excited states, are corrected for the effects of the fast-beam electrons     

温稠密钛电导率计算

温稠密物质是惯性约束核聚变、重离子聚变、Z箍缩动作过程中物质发展和存在的重要阶段. 其热力学性质和辐射输运参数在聚变实验和内爆驱动力学模拟过程中有至关重要的作用. 本文通过建立非理想Saha方程, 结合线性混合规则的理论方法模拟了温稠密钛从10^-5-10 g·cm^-3, 10⁴ K到3×10⁴ K区间的粒子组分分布和电导率随温度密度的变化, 其中粒子组分分布由非理想Saha方程求解得到. 线性混合规则模型计算温稠密钛的电导率时考虑了包括电子、原子和离子之间的多种相互作用. 钛的电导率的计算结果与已有的爆炸丝实验数据相符. 通过电导率随温度密度变化趋势判断, 钛在整个温度区间, 密度0.56 g·cm^-3时发生非金属相到金属相相变. 对于简并系数和耦合系数的计算分析, 钛等离子体在整个温度和密度区间逐渐从弱耦合、非简并状态过渡到强耦合部分简并态.     

Self-reflection of intense electromagnetic waves in plasmas

A uniform electromagnetic wave of high power density, propagating in a collisional plasma gives rise to a modification in temperature-dependent collision frequency and in turn induces a gradient in the complex refractive index of the medium. A WKB solution of the problem predicts a backward propagating wave on account of the self-induced inhomogeneity. The amplitude of the backward (i.e. reflected) wave increases with increasing power density of the wave. This is a volume nonlinear effect and is appreciable for usually employed power densities.     

Hot electrical conductivity in lower hybrid current drive plasmas in the HT-7 tokamak

The interaction between the hot electrical conductivity and the residual electric field have been investigated in lower hybrid current drive (LHCD) experiments with non-zero loop voltage in the HT-7 tokamak. It has been found that the hot electrical conductivity contribute significantly to the current drive in partial non-inductively sustained plasmas. The hot electrical conductivities under different lower hybrid power levels and different parallel refractive indexes have been obtained. It is comparable to the Spitzer conductivity in high power LHCD experiments.     

Directionality of terahertz emission from photoinduced gas plasmas

Forward and backward terahertz emission by ionizing two-color laser pulses in gas is investigated by means of a simple semianalytical model based on Jefimenko's equations and rigorous Maxwell simulations in one and two dimensions. We find the emission in the backward direction has a much smaller spectral bandwidth than in the forward direction and explain this by interference effects. Forward terahertz radiation is generated predominantly at the ionization front and is thus almost not affected by the opacity of the plasma, in excellent agreement with results obtained from a unidirectional pulse propagation model.     

Picosecond x-ray laser interferometry of dense plasmas

We present the first results from picosecond interferometry of dense laser-produced plasmas using a soft x-ray laser. The picosecond duration and short wavelength of the 14.7 nm Ni-like Pd laser mitigates effects associated with motion blurring and refraction through millimeter-scale plasmas. This enables direct measurement of the electron-density profile to within 10 microm of the target surface. A series of high-quality two-dimensional (2D) density measurements provide unambiguous characterization of the time evolution in a fast-evolving plasma suitable for validation of existing 1D and 2D hydrodynamic codes.     

Measurements of viscosity in pure-electron plasmas

Measurements of the viscosity in quiescent magnetized pure-electron plasmas are up to 10(8) times larger than predicted by classical collisional theory. This strong viscosity is due to long-range " E x B drift collisions" between electrons separated by up to a Debye length. Recent theories of long-range collisions show order-of-magnitude agreement with the measurements, but do not give the observed dependence on the plasma column length. A simple empirical scaling law fits the length and magnetic field dependence surprisingly well.     

Dynamics of intense Langmuir waves in current-carrying plasmas

Basic equations including ponderomotive effects of Langmuir waves in a current-carrying plasma are presented. In such a system, dynamics of an initially monochromatic plasma wave is investigated both analytically and numerically. Various regimes of developed modified decay and modulational instabilities of the wave are modelled by using a macroparticle numerical code. In this way the cooperative nature of both ponderomotive and drift effects supporting plasma heating is demonstrated. The underlying physical processes are discussed and relation to the solar flare theory is suggested.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.It is pleasure to acknowledge the staff members of the Computational Centre at Ondejov for their kind support in performing the numerical computations.     

New source of dense, cryogenic positron plasmas

We have developed a new method, based on the ballistic transfer of preaccumulated plasmas, to obtain large and dense positron plasmas in a cryogenic environment. The method involves transferring plasmas emanating from a region with a low magnetic field (0.14 T) and relatively high pressure (10(-9) mbar) into a 15 K Penning-Malmberg trap immersed in a 3 T magnetic field with a base pressure better than 10(-13) mbar. The achieved positron accumulation rate in the high field cryogenic trap is more than one and a half orders of magnitude higher than the previous most efficient UHV compatible scheme. Subsequent stacking resulted in a plasma containing more than 1.2 x 10(9) positrons, which is a factor 4 higher than previously reported. Using a rotating wall electric field, plasmas containing about 20 x 10(6) positrons were compressed to a density of 2.6 x 10(10) cm(-3). This is a factor of 6 improvement over earlier measurements.     

Au等离子体M带5f-3d跃迁透射谱的理论模拟

基于细致组态(DCA)方法和跃迁系列群 (UTA) 模型,采用全相对论处理并结合量子亏损理论,计算了金Au激光等离子体的M带5f-3d跃迁的透射谱, 给出了金等离子体在不同电子温度和电子密度的时空电离态特性,平均电离度,离子丰度和离子内各能级的布居数,并模拟出Au等离子体的M 带5f-3d跃迁的细致谱线,其计算结果可对激光等离子体透射谱的电子温度和电子密度进行精密诊断.     

Thermodynamics of dense high-temperature plasmas: Semiclassical approach

The pseudopotential model of particle interaction of a semiclassical fully ionized plasma, taking into account both quantum effects at short distances and screening field effects at large distances is developed. Radial distribution functions are investigated and it is shown that a short-range order formation can occur in the system under discussion. Correlation energy of dense high-temperature plasma, existing in astrophysical objects is studied and comparison with other methods is performed.     

X-ray spectrometry of laser-produced aluminum plasmas

X-ray lines and continuum emission from a laser-produced aluminum plasma have been studied. The electron temperature variations during the laser pulse (30 ns) were deduced from time-dependent measurements of intensities of resonance lines (2.5 ns time-resolution). Comparison is made with electron temperature values deduced from ion emission measurements.