固支简支端部边界条件下同轴圆柱壳体的流致不稳定性研究

基于Paiedoussis等同轴圆柱壳体流致不稳定性的数学模型和研究方法，分析了固支－简支端部约束条件下同轴圆柱壳体系统的流致不稳定性，结果表明：同两端固支相比，固支－简支端部边界下壳体系统的失稳临界流速更低。     

热电子发射同轴二极管几何结构对空间电荷限制流的影响

本文基于同轴二极管一维空间电荷限制流经典理论公式,利用CST粒子工作室研究了热电子向外发射同轴二极管二维空间电荷限制流随二极管几何结构参数变化的规律和几何结构对虚阴极产生临界条件的影响。结果表明,二极管修正系数是纵横比的单调递减函数;随阳极半径与阴极半径比值的增大,修正系数逐渐降低;二极管的电压、阳极和阴极半径及阴极长度均会影响虚阴极的产生。本文研究结果将为射频四极管结构设计及优化提供参考和理论依据。     

An Approximate Calculation Method of Flux for Spherical and Cylindrical Sources with a Slab Shield

An approximate calculation method for unscattered flux from spherical and cylindrical sources with a slab shield is presented. The method is based on modifying the source geometry to a form convenient for calculation: The sphere is approximated by a conical fragment of spherical shell, and the cylinder by a columnar fragment of cylindrical shell. The procedure for manual calculation is relatively simple, and the difference between results of appoximate and exact calculations is less than +5% for large sources (μ ^s R⁰≦ 4), and±15% for small sources (μ_sR⁰≈0.25). Graphs of the functions for approximate calculation are presented. The method has several advantages over Rockwell's method.     

Numerical Solutions to Critical Problem of Reflected Cylindrical Reactor

The multi-region critical problem can be transformed into an eigenvalue problem in the classical sense by using the method of Kuscer & Corngold and of Wing. This transformation is applied to derive a variational formulation for a reflected reactor.

An approximate critical value of the multiplying factor is determined by maximizing the Rayleigh quotient for radially and totally reflected cylindrical reactors. It is shown that this approximate critical value is an upper bound of the true critical value.

From the facts that the operator is self-adjoint and the eigenfunction is positive, an expression is derived for the upper and lower bounds of the true eigenvalue, by making use of the approximate distribution. The difference of the upper and lower bounds is an uncertainty of the presumption of the true critical value. It is found that we can compute the bounds to any required precision.

The narrow bounds are calculated for two radially and one totally reflected cylindrical reactors.     

Analytical Solutions of Pressure Effects upon Current Transmission across a Diode

Space-charge limiting of current transmission can be neutralized by introducing gas into the diode. The relationship between gas pressure and transmitted current is determined by a combination of several basic physical processes. A model that can predict experimental observations over a wide range of pressures is utilized to show which processes dominate current transmission in various pressure ranges of interest. The quantitative analytical solutions of this model can be correlated with experimental results to yield effective values for secondary electron production, secondary electron drift velocity, electron range effects, and ionization avalanche. Figure 1 shows a typical diode geometry.     

Solutions of Diffusion Equations in Two-Dimensional Cylindrical Geometry by Series Expansions

Abstract

A solution of the multi-group multi-regional diffusion equation in two-dimensional cylindrical (p-z) geometry is obtained in the form of a regionwise double series composed of Bessel and trigonometrical functions.

The diffusion equation is multiplied by weighting functions, which satisfy the homogeneous part of the diffusion equation, and the products are integrated over the region for obtaining the equations to determine the fluxes and their normal derivatives at the region boundaries. Multiplying the diffusion equation by each function of the set used for the flux expansion, then integrating the products, the coefficients of the double series of the flux inside each region are calculated using the boundary values obtained above.

Since the convergence of the series thus obtained is slow especially near the region boundaries, a method for improving the convergence has been developed. The double series of the flux is separated into two parts. The normal derivative at the region boundary of the first part is zero, and that of the second part takes the value which is obtained in the first stage of this method. The second part is replaced by a continuous function, and the flux is represented by the sum of the continuous function and the double series.

A sample critical problem of a two-group two-region system is numerically studied. The results show that the present method yields very accurately the flux integrals in each region with only a small number of expansion terms.     

Effective Cadmium Cutoff Energies for Cylindrical Detectors with Cylindrical Filters

The effective cutoff energies for cylindrical detectors with cylindrical filters in isotropic neutron flux were studied. The reactor spectra used in calculating the effective cutoff energy were those for infinite homogeneous media using the free gas model of deuterium and carbon. The values of the effective cutoff energies for cylindrical geometry in isotropic neutron flux are intermediate between those in isotropic and beam neutron fluxes for slab geometry. Change of detector position in the filter considerably influences the value of the effective cutoff energy. The self-shielding effect is negligibly small in micro counters.     

Plasma Coaxial Discharge for Thin Film Deposition

A coaxial discharge, of 6 capacitors each with 7.71 μF, is used to explore plasma thin film coating by insert a graphite powder at the breach of the coaxial head. Plasma current sheath reached 25 kA, after 10 μs from the start of the discharge. The     

Relativistic atomic structure calculations for highly ionized atoms

Characteristics of the GRASP package for relativistic atomic structure calculations are outlined, together with applications to highly ionized atoms. Transitions with Δn = 0 in helium-like ions and in dielectronic satellites of interest in plasma diagnostics and solar flare spectra provide particularly successful examples of its use. More fundamental studies of atomic structure theory can be based on a numerical decomposition of the energy into terms proportional to different powers of α². The use of this approach in analysing recent experiments to test QED through measurement of the 1s2s ³S-1s2p ³P intervals in the helium isoelectronic sequence is discussed.     

An Attempt to Study on the Growth and Damping Rates with Approximate Solutions by Using Mathematical Models

As is already known, most of the plasma literature is occupied with the plasma instabilities and the inevitable plasma waves, which remain major obstacles to the thermonuclear fusion process. Many experimental data on the plasma waves （growth or damping） and their accompanied theoretical interpretations have been published during the last five decades; lots of them have been identified and justified as well, some not yet. One of these is our previous research on plasma waves, which originated in the early 80＇s at the Plasma Physics Laboratory of the NCSR ＂Demokritos＂. As the wave rising is defined by the growth rate （or the damping on the extinguishment）, these important wavy quantities will be studied in detail in the present paper. Three examples are taken from our previous theoretical results, and the first observation reveals that the involved quantities are complicated enough to be studied by themselves. So, the use of suitable approach models, which may interpret the experimental wavy quantities, is the central idea of the present attempt, Furthermore, calculations with a little change of the initial conditions have been repeated in order to determine whether the plasma behaves as a chaotic medium.     

一维自然循环比例分析的理论模型

整体性能试验研究是验证先进非能动压水堆核电站堆芯冷却系统设计有效性的核心技术,一回路系统两相自然循环热工水力特性比例分析是确定整体性能试验装置尺度的主要理论依据。以一维漂移流模型为基础,对整个一回路两相自然循环系统控制方程积分,并求得稳态解,由此获得了系统的流动条件。应用初始流动条件与边界条件,对两相自然循环系统控制方程直接无量纲化,最终得到了整体性能试验装置与实际非能动电站热工水力特性的相似准则。     

同轴型HpGe探测器离子注入工艺仿真

为了进一步优化同轴型高纯锗探测器离子注入工艺参数,利用Silvaco半导体仿真软件和SRIM离子注入仿真软件对离子注入过程进行模拟,研究不同注入角度、能量、剂量对注入的均匀性、深度、杂质浓度分布及损伤的影响,并根据模拟结果选择合适的工艺参数,为HpGe探测器的制备提供一定的指导。此外,研究了离子注入后退火的温度及时间对晶格损伤恢复和杂质激活的影响情况。     

Simplified Engineering Techniques for Predicting Diode Tree Responses

The feasibility of predicting equilibrium photocurrents in silicon switching diodes entirely from nondestructively measured electrical parameters is shown. The prediction method is derived from the basic theoretical equation for diode photocurrent. Junction areas and depletion widths are related to avalanche voltages and capacitance-voltage characteristics by a general solution to McKay's avalanche condition integral equation. Diffusion lengths are related to storage times. The feasibility of the prediction method is demonstrated by comparing predicted and measured values of equilibrium photocurrents in 46 test diodes.     

Relativistic radiationless transition probabilities for atomic K- and L-shells

Auger and Coster-Kronig transition probabilities have been calculated ab initio relativistically from perturbation theory, for frozen orbitals, in the Dirac-Hartree-Slater approach. Results in the j?j coupling scheme are tabulated for ≥22 elements with atomic numbers 18 ≤ Z ≤ 96.     

Miniature Coaxial Plasma Injector for Diagnostics by Beam Plasma Interaction

A miniature coaxial gun has been used to study the interaction between plasma beam and low density plasma formed in glow discharge. The peak discharge current flow between the coaxial electrodes was 5.25 kA as a single pulse with pulse width     

反应堆一维两流体模型二阶精度数值解法研究

探索一维两流体模型的二阶精度算法,并将其用于一阶精度程序TFIT,开发出二阶精度程序,采用flux limiter计算对流项,并采用表面张力加强数值解法的稳定性。通过对经典的不连续两流体冲击问题——water faucet问题进行模拟,得到冲击波在管内的前行过程,将二阶与一阶程序和精确解进行对比,结果表明:二阶精度的程序精度明显提高,其稳定性与一阶精度的程序保持一致,并能更好地捕捉管内冲击波。     

一维自然循环比例分析的结果与讨论

根据一维自然循环比例分析理论模型推导的试验装置与实际电站热工水力特性的相似准则,对整体性能试验装置主要参数的确定方法进行了深入讨论。结果表明:采用小尺度、等压力、同工质的实验装置模拟实际系统自然循环现象更为准确实际,单相和两相自然循环比例准则可同时满足,不存在复杂比例变化带来的失真,不利因素是试验成本偏高。同工质非等物性(不等压)模拟能够降低试验成本,但比例参数不能满足从单相自然循环到两相自然循环的平滑过渡。如保持功率连续,其速度比和特征时间比会有所差异。     

一维位置灵敏电阻阳极低能重离子探测器

本文讨论了微通道板电阻阳极低能重离子探测器的原理，给出了已研制成功的位敏电阻阳极离子探测器的结构和信号分析电子学线路。用￣（２３８）Ｐｕα放射源测量了位敏探测器在有效面积范围内的位置信号、位置线性和位置分辨。位置分辨好于０．３ｍｍ，已满足了离子原子碰撞的实验要求。     

Approximate Calculation Method for Second Order Sensitivity Coefficient

A simple method has been developed for calculating the second order sensitivity coefficient of static and burnup-dependent core performance parameters. The method is applied to a small and a large fast breeder reactors. Changes in core performance parameters due to 10% cross section changes are compared with that predicted by the first and the second order sensitivity analyses. Numerical results reveal that the changes in breeding ratio, reaction rate ratio of the ²³⁸U capture to the ²³⁹Pu fission rate and burnup reactivity loss due to the 10% change in the ²³⁹Pu fission cross section and/or the ²³⁹Pu v-value show nonlinear behavior, and the second order sensitivity can predict the changes accurately.