Raman amplification with reduced polarization impairments in the fibre with tailored spin profile

By using two-section fibre where the first section has no spin and the second one is periodically spun, we demonstrate reduced polarization dependent gain and polarization mode dispersion (0.3 dB and 0.0072 ps·km^−1/2 correspondently) in a distributed fibre Raman amplifier.     

Tailoring steep density profile with unstable points

The mesoscopic properties of a plasma in a cylindrical magnetic field are investigated from the view point of test-particle dynamics. When the system has enough time and spatial symmetries, a Hamiltonian of a test particle is completely integrable and can be reduced to a single degree of freedom Hamiltonian for each initial state. The reduced Hamiltonian sometimes has unstable fixed points (saddle points) and associated separatrices. To choose among available dynamically compatible equilibrium states of the one particle density function of these systems we use a maximum entropy principle and discuss how the unstable fixed points affect the density profile or a local pressure gradient, and are able to create a steep profile that improves plasma confinement.     

Electron momentum density and Compton profile by a semi-empirical approach

Here we propose a semi-empirical approach to describe with good accuracy the electron momentum densities and Compton profiles for a wide range of pure crystalline metals. In the present approach, we use an experimental Compton profile to fit an analytical expression for the momentum densities of the valence electrons. This expression is similar to a Fermi–Dirac distribution function with two parameters, one of which coincides with the ground state kinetic energy of the free-electron gas and the other resembles the electron–electron interaction energy. In the proposed scheme conduction electrons are neither completely free nor completely bound to the atomic nucleus. This procedure allows us to include correlation effects.We tested the approach for all metals with Z=3–50 and showed the results for three representative elements: Li, Be and Al from high-resolution experiments.     

Covariant polarization density matrix for pure states of particles with integral spin

A closed expression is obtained for the covariant polarization density matrix of pure states of particles with integral spin. The application of the results to the decay f⁰ is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 111–115, August, 1977.I am very grateful to A. B. Govorkov for his interest in the work and valuable comments. I am also very grateful to B. Z. Kopeliovich for a helpful discussion.     

Sharp hollow density profile with TVTS on ECRH JFT-2M plasma

The first hollow electron density profile in the central region is measured during the electron cyclotron resonance heating (ECRH) on the JFT-2M tokamak with a TV Thomson scattering system. The density of the peripheral region is not hollow but is accumulated by the pump out from the central region and the gas puffing from outside. The hollowness increases with time but is saturated at ∼ 40 ms and maintains the constant hollow ratio in spite of a slight decrease of temperature. The hollowness is strongly connected with the steep temperature gradient of the heated zone.     

Valley density profile for highly efficient x-ray lasers with good beam quality

A plasma with a valley density profile at the required electron density for high-gain operation of an x-ray laser could be obtained using a normally incident 300 ps laser pulse followed by a grazing-incident 300 ps laser pulse. Sudden heating of the valley plasma region by another grazing-incident 300 fs laser pulse would then yield a highly efficient x-ray laser beam with a deflecting angle of 2 mrad and a divergence angle of 4 mrad. Saturation operation of the x-ray laser beam at 32.6 nm could be achieved with a total pump energy of less than 100 mJ.     

Intense laser beam propagating in a plasma channel with flat-bottom leaky density profile

The propagation characteristics of an intense laser beam in a preformed plasma channel with the flat-bottom leaky density profile are investigated in detail. The evolution equation of the laser spot size is derived by employing variational technique. Seven propagation modes of the laser spot size are identified and some numerical results are presented. By comparison, we find that the results in this Letter may be more realistic since the flat-bottom leaky plasma channel comes closer to the practical plasma channel.     

瑞利-泰勒不稳定性线性增长的密度梯度致稳

研究了密度梯度对瑞利-泰勒不稳定性的致稳作用,采用有限元算法求解钱得拉塞卡方程本征值问题,得到不同密度分布下理想不可压流体力学量的扰动线性增长率及扰动速度分布。扰动增长率结果与修正的Lindl公式的计算结果比较发现：扰动分布的峰值位于密度梯度标长的取值位置处,波长与密度标长可比拟时,扰动增长率显著偏离Lindl公式,而长波和短波极限情况下,数值解和Lindl公式符合较好。     

瑞利-泰勒不稳定性线性增长的密度梯度致稳

 研究了密度梯度对瑞利-泰勒不稳定性的致稳作用,采用有限元算法求解钱得拉塞卡方程本征值问题,得到不同密度分布下理想不可压流体力学量的扰动线性增长率及扰动速度分布。扰动增长率结果与修正的Lindl公式的计算结果比较发现：扰动分布的峰值位于密度梯度标长的取值位置处,波长与密度标长可比拟时,扰动增长率显著偏离Lindl公式,而长波和短波极限情况下,数值解和Lindl公式符合较好。     

Evaluation of the density matrix for an ensemble of anharmonic oscillators by a path integral approach

Considering the Feynman path integral representation for the configuration-space density matrix for an ensemble of anharmonic oscillators, we determine the stationary paths near which the integrand remains stationary. By taking the path integral to be saturated by contributions from the neighborhood of the path which maximizes the integrand we evaluate the density matrix explicitly in analytic form. This seems to be the first such evaluation of a path integral for a system not describable by a quadratic Hamiltonian. We also comment briefly on the question of analyticity with respect to the perturbation parameter.     

Evolution of the current density profile associated with magnetic island formation in JT-60U

Evolution of the current density profile associated with magnetic island formation of an m/n=2/1 tearing mode was measured using a motional Stark effect (MSE) diagnostic for the first time in the JT-60U tokamak. With the island growth, the current density profile turned flat at the radial region of the island, followed by an appearance of a hollow structure. As the island shrank, the flat region became narrower, and it finally diminished after the disappearance of the island. The fluctuation of the local poloidal magnetic field from MSE showed a strong correlation with a slow island rotation. This indicates that the observed deformation in the current density profile is localized at the island O point.     

HL-2A装置电子密度多道干涉测量实验系统

电子密度是核聚变等离子体研究中的一个主要物理参数,为获取电子密度时空分布的准确信息,结合HL-2A装置结构特点设计并建立了八道FIR激光干涉仪测量系统。在长光路的布局中采用了介质波导传输,研制了长谐振腔高功率HCN波导激光器。另外为减少干扰影响在差拍信号数据采集电子学中采用了数字锁相滤波FPGA技术, 并用软件和硬件两种相位比较方法监测电子密度,实现了密度随时间变化的实时显示。在等离子体放电中干涉仪系统测量精度可达1/33条纹,相应密度约为1.3×10¹¹cm^-3,时间分辨为0.1ms。     

Experimental study of a swept reflectometer with a single antenna for plasma density profile measurement

The feasibility of a swept microwave reflectometer, with one antenna only, for plasma electron density measurement is studied. Experimental results obtained in the laboratory by simulating the plasma with a metallic mirror are presented.Permanent address Departamento de Electromagnetismo Facultat de Ciencas-Universitad de Santander Avda los Castros s/n Santander-Spain     

Local density of states of a finite-sized rectangular-lattice photonic crystal with separable profile of permittivity

A different approach in the calculation of two-dimensional local density of states has been presented for a two-dimensional finite rectangular-lattice photonic crystal with a separable profile of permittivity. Approximate staircase structures are already shown to be useful for their ability to reproduce actual properties of practical square lattice photonic crystals. Using the effective resonance approach in a Fabry–Perot resonator and transfer matrix method an analytical expression for calculating a two-dimensional local density of states can be derived for both polarisations in the structure. It is shown that for this geometry one can resolve the modes as a product of two separate functions each being a function of x- and y-coordinates. The results have been investigated for the two-dimensional local density of states in the ordered finite structure and in the disordered structure. The main advantage of this method in calculating the local density of states is its extremely efficient numerical evaluations. As an application we introduce a cavity-like defect in the vicinity of a waveguide-like defect and examine the variation of local density of states in the plane of the structure at band gap frequency.     

Optimum hot electron production with low-density foams for laser fusion by fast ignition

We propose a foam cone-in-shell target design aiming at optimum hot electron production for the fast ignition. A thin low-density foam is proposed to cover the inner tip of a gold cone inserted in a fuel shell. An intense laser is then focused on the foam to generate hot electrons for the fast ignition. Element experiments demonstrate increased laser energy coupling efficiency into hot electrons without increasing the electron temperature and beam divergence with foam coated targets in comparison with solid targets. This may enhance the laser energy deposition in the compressed fuel plasma.     

In depth fusion flame spreading with a deuterium-tritium plane fuel density profile for plasma block ignition

<正>Solid-state fuel ignition was given by Chu and Bobin according to the hydrodynamic theory at x = 0 qualitatively. A high threshold energy flux density,i.e.,E^* = 4.3×10¹² J/m²,has been reached.Recently,fast ignition by employing clean petawatt-picosecond laser pulses was performed.The anomalous phenomena were observed to be based on suppression of prepulses.The accelerated plasma block was used to ignite deuterium-tritium fuel at solid-state density. The detailed analysis of the thermonuclear wave propagation was investigated.Also the fusion conditions at x≠0 layers were clarified by exactly solving hydrodynamic equations for plasma block ignition.In this paper,the applied physical mechanisms are determined for nonlinear force laser driven plasma blocks,thermonuclear reaction,heat transfer, electron-ion equilibration,stopping power of alpha particles,bremsstrahlung,expansion,density dependence,and fluid dynamics.New ignition conditions may be obtained by using temperature equations,including the density profile that is obtained by the continuity equation and expansion velocity.The density is only a function of x and independent of time.The ignition energy flux density,E_t^*,for the x≠0 layers is 1.95×10¹² J/m².Thus threshold ignition energy in comparison with that at x = 0 layers would be reduced to less than 50 percent.     

飞秒强激光作用下线性等离子体层中光场和电子密度的自洽分布

自洽求解了圆偏振的飞秒强激光作用下线性等离子体层中光场和电子密度的分布.研究发现在激光有质动力的作用下，电子密度分布严重偏离离子密度分布，甚至出现了一系列的“电子岛”和“电子空腔”.由于电荷分离，等离子体内形成了很强的静电场，一部分激光能量转化为等离子体内的静电能.线性等离子体层储存静电能的大小随着入射激光强度的增加而显著上升. 关键词： 飞秒激光 相对论等离子体 电子密度 有质动力     

profile measurement by projecting two gratings with different pitches

A new method for measuring objects with steps is proposed in which two gratings with different pitches are projected on the object surLace. The method is demonstrated with sinusoidal gratings made of laser interference fringes and also sinusoidal gratings formed by liquid crystal controlled by computer. An object with step height of 20 mm is measured with standard variation below 3%.     

Cathodic-arc plasma density, radial profile, and total plasmainventory as measured by microwave interferometer and Faraday cup

The total amount of plasma, peak plasma density, and plasma density radial profile are derived from a series of measurements of ion current density (with a Faraday cup) and integrated electron line density (with a microwave interferometer) for a cathodic arc derived plasma. Comparisons are made between cathode material (erbium and titanium), arc current, background gas pressure, and the presence or absence of a series magnetic solenoid around the coaxial anode and cathode