Unlike-particle collision operator for gyrokinetic particle simulations

Plasmas in modern tokamak experiments contain a significant fraction of impurity ion species in addition to main deuterium background. A new unlike-particle collision operator for δf particle simulation has been developed to self-consistently study the non-local effects of impurities on neoclassical transport in toroidal plasmas. A new algorithm for simulation of cross-collisions between different ion species includes test-particle and conserving field-particle operators. The field-particle operator is designed to enforce conservation of number, momentum and energy. It was shown that the new operator correctly simulates the thermal equilibration of different plasma components. It was verified that the ambipolar radial electric field reaches steady state when the total radial guiding center particle current vanishes.     

Photoionization of the excited He atom in Debye plasmas

We present theoretical photoionization cross sections for He 1s2s ¹S and He 1s2p ¹P states in a Debye plasma environment by the complex coordinate rotation method, using a finite L² basis set constructed from one electron Laguerre orbitals. The plasma environment is found to appreciably influence the photoionization cross sections near the ionization threshold. In this regard, the photoionization cross sections of isolated He are compared with other theoretical and experimental results. Our results are in good agreement with the previous results. A new minimum appears in the photoionization cross section curve for the metastable 1s2s ¹S state. Results are given for the S- and D-wave partial photoionization for the excited 1s2p ¹P state.     

Surface characterization and growth mechanism of laminated Ti3SiC2 crystals fabricated by hot isostatic pressing

Laminated Ti₃SiC₂ crystals were prepared by hot isostatic pressing from Ti, Si, C and Al powders with NaCl additive in argon at 1350 °C. The morphology and microstructure of Ti₃SiC₂ crystals were investigated by means of XRD, SEM, and TEM. The high symmetry and crystalline was revealed by high resolution transmission electronic microscope (HRTEM) and selected area electron diffraction (SAED). The growth mechanism of Ti₃SiC₂ crystals controlled by two-dimensional nucleation was put forward. The growth pattern of layered steps implies that the growth of the (0 0 2) face should undergo two steps, the intermittent two-dimensional nucleation and the continuous lateral spreading of layers on growth faces.     

The 60° or 180° twinned Bi-doped PbTe film studied by EBSD

The Bi-doped PbTe film was grown on Si(1 1 1) substrate by using hot wall epitaxy (HWE) technique. The film was characterized by means of scanning electron microscopy, micro-area X-ray diffraction and electron backscatter diffraction (EBSD). The results indicate that the film is dominated by 〈1 1 1〉 orientation. The film consists of two twinned domains, rotated 60° or 180° around the normal to the film surface. It is speculated that the twinned PbTe film results from the deviated triangular grains. The ratio between the grains with two different orientations will decrease with the increase of the film thickness.     

Variational method for the nonlinear dynamics of an elliptic magnetic stagnation line

The nonlinear evolution of the kink instability of a plasma with an elliptic magnetic stagnation line is studied by means of an amplitude expansion of the ideal magnetohydrodynamic equations. Wahlberg et al. [12] have shown that, near marginal stability, the nonlinear evolution of the stability can be described in terms of a two-dimensional potential U(X,Y), where X and Y represent the amplitudes of the perturbations with positive and negative helical polarization. The potential U(X,Y) is found to be nonlinearly stabilizing for all values of the polarization. In our paper a Lagrangian and an invariant variational principle for two coupled nonlinear ordinal differential equations describing the nonlinear evolution of the stagnation line instability with arbitrary polarization are given. Using a trial function in a rectangular box we find the functional integral. The general case for the two box potential can be obtained on the basis of a different ansatz where we approximate the Jost function by polynomials of order n instead of a piecewise linear function. An example for the second order is given to illustrate the general case. Some considerations concerning solar filaments and filament bands (circular or straight) are indicated as possible applications besides laboratory experiments with cusp geometry corresponding to quadripolar cusp geometries for some clouds and thunderstorms.     

常压介质阻挡放电的特性研究及应用前景

常压介质阻挡放电由于其具有均匀、散漫、稳定,而且不需要真空系统等优点,正日益受到人们的重视和研究。文章给出了常压介质阻挡放电的研究进展,包括实验装置、实验条件、放电机理以及最新的诊断方法,还介绍它在材料表面改性、环境工程、食品加工等方面的应用前景。     

超强激光-等离子体相互作用过程中的辐射阻尼效应

基于包含辐射阻尼效应的电子运动方程,通过坐标变换,分析了圆极化和线极化超强激光在等离子体中传播时,辐射阻尼效应对电子运动的影响。结果表明:两种极化情况下,辐射阻尼效应都随等离子体密度的增大而增强;在圆极化激光中,激光强度在1023~1026 W/cm2范围(对应于不同的等离子体密度)时,辐射阻尼效应将对电子的运动产生显著的反作用,而对于线极化激光,只有当激光强度远大于极限光强时,辐射阻尼效应才对电子的运动有明显的作用。     

液体冷媒融霜系统回液时间的实验研究

对液体冷媒融霜系统的回液时间进行实验研究。在保温体温度-15℃工况下分别对回液时间7s、27s、25s、30s、40s、50s进行实验,记录并分析被融霜蒸发器融霜前和回液时间内压缩机吸气口的温度和压力变化,相机拍摄制冷压缩机吸气口和机身的结霜状况。实验表明:回液时间7s时,压缩机吸气过潮,回液时间在27s左右可以避免压缩机吸气过潮,确保系统安全正常的运行,大于27s被融霜蒸发器恢复制冷时间过长将影响库房温度的稳定并降低制冷系统的效率。     

Effect of Discharge Plasma Potential on Diffusion Plasma Parameters Controlled by a Mesh Grid in a Double Plasma Device

The plasma region under investigation is separated from the discharge region by a mesh grid. Plasma potential and electron number densities and electron temperatures under bi‐Maxwellian approximation for electron distribution function of the multi‐dipole argon plasma are measured. The cold electrons in the diffusion region are produced by local ionization. The hot electrons are the ionizing electrons behaving as Maxwellian. The electron trapping process in the discharge region is produced by potential well due to positive plasma potential with respect to the anode and by a repulsive grid. The dependence of ratios of the density of the hot to the cold electrons N_E (=N_eh/N_ec) and hot to cold electron temperature T(=T_eh/T_ec) in the diffusion region on the depth of the potential well has been investigated. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)