Impurity transport in the model of a dual-porosity regularly heterogeneous medium with colloids

The problem of impurity advection in a channel surrounded by a weakly permeable medium with drifting colloidal particles present in the channel is solved. A regime in which the front of the impurity cloud moves with a constant velocity and the concentration behind the front decreases as a power law is established due to the impurity adsorption on colloids and its diffusive exchange with the matrix on moderate time scales. On long time scales, the transport in the channel is quasi-diffusive as a result of the impurity desorption and its eventual escape into the matrix.     

Effect of ultrasound power on HCl leaching kinetics of impurity removal of aphanitic graphite

This study aimed to investigate the effect of ultrasonic power and temperature on the impurity removal rate during conventional and ultrasonic-assisted leaching of aphanitic graphite. The results showed that the ash removal rate increased gradually (∼50 %) with the increase in ultrasonic power and temperature but deteriorated at high power and temperature. The unreacted shrinkage core model was found to fit the experimental results better than other models. The Arrhenius equation was used to calculate the finger front factor and activation energy under different ultrasonic power conditions. The ultrasonic leaching process was significantly influenced by temperature, and the enhancement of the leaching reaction rate constant by ultrasound was mainly reflected in the increase of the pre-exponential factor A. Ultrasound treatment improved the efficiency of impurity mineral removal by destroying the inert layer formed on the graphite surface, promoting particle fragmentation, and generating oxidation radicals. The poor reactivity of hydrochloric acid with quartz and some silicate minerals is a bottleneck limiting the further improvement of impurity removal efficiency in ultrasound-assisted aphanitic graphite. Finally, the study suggests that introducing fluoride salts may be a promising method for deep impurity removal in the ultrasound-assisted hydrochloric acid leaching process of aphanitic graphite.     

HL-lM装置杂质粒子输运与约束特性

在HL-lM装置上利用激光吹气技术,在等离子体边缘瞬态注入少量Al杂质粒子,通过对真空紫外光谱和软X射线区的杂质辐射测量,分别研究了欧姆等离子体和低杂波电流驱动等离子体两种情况下,Al杂质粒子输运与约束特性。结果表明：在欧姆等离子体和低杂波电流驱动等离子体两种情况下,等离子体中心区,在没有MHD锯齿震荡和有MHD锯齿震荡非锯齿破裂期间,杂质粒子输运基本上受新经典规律支配;在有MHD锯齿震荡锯齿破裂期间,杂质粒子输运受MHD不稳定性支配,但其时间很短(通常小于300μs),所以在这种情况下,杂质粒子输运的平均效应比新经典值稍大。而约束区杂质粒子输运则比新经典的值大很多,是反常的。在一定条件下低混杂波电流驱动可以改善等离子体粒子约束。     

Preliminary analysis of impurity transport in HL-2A ohmic discharges

This paper describes the behaviour of impurity transport in HL-2A ohmic discharges. In 2005, small quantities of metallic impurities （A1, Ni and Ti） were successfully injected into HL-2A plasmas by laser blow-off technique, and their progression was followed by the soft x-ray cameras with good spatial and temporal resolutions. The impurity confinement time is estimated from the characteristic decay time of the soft x-ray signal of the injected impurities, and it is about 30-60 ms. The transport coefficients of impurities （including diffusion coefficient and convection velocity） in radial different region have been derived by using a one-dimenslonal impurity transport code, the results present that diffusion coefficient is much smaller in the central region of plasmas than the outside of it, and it is much larger than that of neoclassical theory predictions; namely, it is anomalous.[第一段]     

The formation of heavy-fermion states in non-Fermi-liquid impurity systems

A mechanism for the occurrence of heavy-fermion states in non-Fermi-liquid (NFL) metals with f-shell impurities is proposed. The impurity with an unstable valence is suggested to have an energy spectrum consisting of a deep f-level and quasicontinuum states (narrow band) in resonance with the Fermi energy. Depending on the impurity concentration, the single-site NFL states are generated by the two-channel Kondo scattering for the low concentration (the Kondo regime) or by the screening interaction for a relatively high concentration (the X-ray-edge regime). It is shown that the NFL states are unstable against the scattering of the NFL excitations by electron states of the narrow band. This scattering generates additional narrow Fermi-liquid (FL) resonances at/near the Fermi level in the Kondo regime and in the X-ray-edge regime. The mixed-valence states are shown to be induced by new FL resonances. The mixed valence mechanism is local and is related to the instability of single-site NFL states. The FL resonances lead to the existence of additional energy scales and of pseudogaps near the Fermi level in the mixed-valence states. They also considerably narrow the region with a nearly integer valence.     

CT-6B托卡马克装置上电流上升阶段电子温度的光谱测量

在CT-6B托卡马克装置上,用一米掠入射真空紫外单色仪测量了氧杂质各阶离子OII-OVI的谱线辐射的时间变化,用HCN远红外激光干涉仪测量了电子密度的时间变化。利用谱线时间史的方法,由谱线起始时间估算了放电初期电流上升阶段电子温度的时间变化。用数值计算分别考察了氧杂质进入通量和约束时间对谱线峰值强度和起始时间的影响。估算得到的电子温度在放电开始后0.36,0.56,0.66,0.90和1.4ms,分别为3.6,5.6,7.3,10.8和21eV,它们反映了放电初期等离子体中心区电子温度的变化。 关键词：     

Kinetics of impurity segregation at grain boundaries in polycrystals. II. Concentrated solution

The isothermal impurity segregation from a finite-size grain into an intergrain boundary region or at an external free surface is investigated when the impurity concentration in the boundary region is not small. Simple algebraic equations are obtained that describe the impurity concentration for the case of several competing and interacting impurities. The process of segregation of two impurities is discussed in detail, and it is shown that the concentration of one of them can have a maximum as a function of time. Fiz. Tverd. Tela (St. Petersburg) 40, 251–253 (February 1998)     

Manifestation of superfluidity in an evolving Bose-Einstein condensed gas

We study the generation of excitations due to an "impurity" (static perturbation) placed into an oscillating Bose-Einstein condensed gas in the time-dependent trapping field. It is shown that there are two regions for the position of the local perturbation. In the first region the condensate flows around the impurity without generation of excitations demonstrating superfluid properties. In the second region the creation of excitations occurs, at least within a limited time interval, revealing destruction of superfluidity. The phenomenon can be studied by measuring the damping of condensate oscillations at different positions of the impurity.     

Some comments on Kondo lattices and the Mott transition

The so called exhaustion problem occurs when few electrons have to screen many spins in a metal with magnetic impurities. A singlet Fermi liquid ground state is possible only if all impurities are “isotropized” in such a way as to suppress their entropy. That takes a time and the corresponding energy limits the Fermi liquid range. The present note explores that issue of time and energy scales, and it concludes that is much smaller than the single impurity Kondo temperature. Similarly the relevant energy scale is proportional to the number of electrons. Recent results on the Mott metal insulator transition in infinite dimension are reconsidered in the light of these results: controversies in that respect are shown to reduce to a simple physical question, with no firm answer as to now. Received: 5 May 1998 / Received in final form and Accepted: 29 July 1998     

Time-dependent plasma transport simulation for the study of edge impurity radiation dynamics with magnetic island in large helical device

The dynamics of impurity radiation distribution during detachment transition with edge magnetic island induced by the application of resonant magnetic perturbation (RMP) is studied numerically by solving time-dependent plasma fluid equations together with impurity and neutral transports in a 2D grid system. Computations provide the appearance of a macroscopic structure in the heat transfer along the island separatrix and outside the island. The resultant parallel temperature gradient generates the plasma flow and the density gradient according to the parallel momentum balance. The resulting plasma flow effectively transports impurity towards the X-point region. As a result, the impurity radiation is more intense near the X-point than in the vicinity of the O-point. This leads to the predominant cooling of the region around the X-point. These results are in agreement with experimental observation with RMP application in the large helical device (LHD). The time scale of the thermal condensation instability is found to be of the order of 10 ms.     

Relationship between characteristics of steady and nonsteady impurity capture processes in molecular beam crystallization

Doping processes using molecular beam epitaxy are considered using a model of impurity in fractures. Expressions for depth of the transition region d_t the steady state impurity concentration in the crystal x _B ^st and the insertion coefficient K_B, all considering fluctuations in the fracture position, are analyzed. A precise expression, convenient for making estimates, is presented for the interrelationship of these characteristics. It is shown that in the region of low crystallization temperatures T and growth rates R typical of molecular beam epitaxy, the transition region thickness d_t is proportional to 1/K_i, where the insertion coefficient depends on R and T. A connection between growth rate R dependences of transition region thickness d_t and steady state impurity concentration x _B ^st is noted. The results obtained are compared with experiment and results of other impurity capture models.Translated from Izvestiya Vysshikh Zavedenii, Fizika, No. 8, pp. 102–107, August, 1995.     

Spin-polarized transient electron trapping in phosphorus-doped silicon

Experimental evidence of electron spin precession during travel through the phosphorus-doped Si channel of an all-electrical device simultaneously indicates two distinct processes: (i) short time scales (≈50 ps) due to purely conduction-band transport from injector to detector and (ii) long time scales (≈1 ns) originating from delays associated with capture or reemission in shallow impurity traps. The origin of this phenomenon, examined via temperature, voltage, and electron density dependence measurements, is established by means of a comparison to a numerical model and is shown to reveal the participation of metastable excited states in the phosphorus-impurity spectrum. This work therefore demonstrates the potential to make the study of macroscopic spin transport relevant to the quantum regime of individual spin interactions with impurities as envisioned for quantum information applications.     

Convective instability of solidification with a phase transition zone

The morphological instability of solidification is analytically studied in the presence of an anisotropic and heterogeneous phase transition zone with allowance for a liquid flow and convective heat-andmass transfer in this two-phase zone. The mechanism of breaking the stability of solidification is considered; it consists in a convective heat and impurity transfer during a liquid flow along channels in the phase transition zone. The morphological instability is subjected to linear analysis with allowance for a liquid flow in the liquid phase of the system, impurity diffusion in the two-phase zone, and the dependence of the transfer coefficients on the phase composition. The perturbation evolution parameter is determined for an anisotropic and heterogeneous two-phase zone, and neutral stability curves of the process are obtained. It is shown that taking into account impurity diffusion and an increase in the heterogeneity of the phase transition zone broaden the instability region and that a decrease in the anisotropy narrows this region. A new criterion of convective morphological instability of solidification with a two-phase zone is found, and it substantially broadens the instability region when the liquid flow velocity increases.     

托卡马克离子温度梯度湍流输运同位素定标修正中杂质的影响

托卡马克实验发现,在不同参数条件下,等离子体能量约束经验定标律会有或大或小的修正.为解释这种修正现象发生的原因,应用回旋动理学方法,对含重(钨)杂质等离子体离子温度梯度(ITG)(包括杂质模)湍流输运的同位素效应进行了数值研究.结果表明钨杂质效应极大地修改了同位素定标律和有效电荷效应.随着杂质离子电荷数Z和电荷集中度f_z的变化,同位素定标律在较大范围内变化. ITG模最大增长率定标大约为M_i~(-0.48→-0.12),杂质模的定标为M_i~(-0.46→-0.3),其中, M_i表示主离子质量数.在ITG模湍流中,有效电荷数越大,关于M_i的拟合指数偏离-0.5越远,表现为同位素质量依赖减弱.在两种模中,杂质电荷集中度越大,同位素质量依赖越弱.研究了杂质效应使定标关系发生偏离的原因,证实杂质种类、杂质电荷数和杂质浓度的不同,是引起同位素质量依赖发生改变的重要原因.结果证实并解释了不同参数条件下托卡马克同位素定标的差异性.研究成果可以为ITER实验安排及杂质相关输运实验中选择装置材料、工作气体和设置其他参数提供理论参考.     

双次曝光积分效应实现杂质浓度分布均匀化

 激光诱导扩散中,当入射激光光强为高斯分布甚至均匀分布时，微小扩散区的温度分布不均匀。由于扩散系数是温度的函数，必将导致扩散后杂质浓度分布的均匀性较差，无法制作出高性能的p-n结。提出采用多次激光诱导扩散的积分效应来实现杂质浓度分布的均匀化整形。对于InP衬底的CO_{2激光诱导Zn扩散,利用温度闭环测控系统测得的基片表面热斑温度场分布，分析计算了两次激光诱导扩散重叠区域的浓度分布积分效应。在此基础上模拟计算出，用双次曝光积分效应做杂质浓度分布的均匀化整形时，基片上两次激光照射位置的最佳间隔为20 μm。这为改进激光诱导扩散工艺，用多次曝光实现面均匀的杂质浓度分布奠定了理论基础。}     

Radiation loss in a compound plasma system with high and low temperature regions

A code has been developed for calculating the non-coronal radiation of impurity in a compound plasma system which consists of high and low temperature regions. The radiation loss of impurity carbon in this system is calculated and analysed. The cooling rate in this system is smaller than that in a homogeneous plasma system due to the particle exchange between the two regions of the system. The volumetric radiation is much bigger in the low temperature region than in the high temperature region because of the relatively low temperature and high electron density, despite the much smaller volume.     

Violation of the Fluctuation-Dissipation Theorem and Heating Effects in the Time-Dependent Kondo Model

The fluctuation-dissipation theorem (FDT) plays a fundamental role in understanding quantum many-body problems. However, its applicability is limited to equilibrium systems and it does in general not hold in nonequilibrium situations. This violation of the FDT is an important tool for studying nonequilibrium physics. In this paper we present results for the violation of the FDT in the Kondo model where the impurity spin is frozen for all negative times, and set free to relax at positive times. We derive exact analytical results at the Toulouse point, and results within a controlled approximation in the Kondo limit, which allow us to study the FDT violation on all time scales. A measure of the FDT violation is provided by the effective temperature, which shows initial heating effects after switching on the perturbation, and then exponential cooling to zero temperature as the Kondo system reaches equilibrium.     

具有不可共度势的掺杂一维体系中波函数的计算

本文将单点杂质引入到不可共度势一维体系中,用格林函数方法推导了杂质状态的能级和波函数。发现当杂质处在不可共度势变化较快的位置时,杂质能级的变化也较大。杂质状态的波函数是略有波动的指数衰减函数。讨论了杂质对带内状态波函数的影响,发现以杂质点为对称的体系中,具有偶宇称的状态波函数,在杂质的附近,振幅有相当大的下降。在对杂质点无对称性的体系中,在杂质的附近,产生一个振幅的阶跃。 关键词：     

Dynamic conductivity modified by impurity resonant states in doping three-dimensional Dirac semimetals

The impurity effect is studied in three-dimensional Dirac semimetals in the framework of a T-matrix method to consider the multiple scattering events of Dirac electrons off impurities. It has been found that a strong impurity potential can significantly restructure the energy dispersion and the density of states of Dirac electrons. An impurity-induced resonant state emerges and significantly modifies the pristine optical response. It is shown that the impurity state disturbs the common longitudinal optical conductivity by creating either an optical conductivity peak or double absorption jumps, depending on the relative position of the impurity band and the Fermi level. More importantly, these conductivity features appear in the forbidden region between the Drude and interband transition, completely or partially filling the Pauli block region of optical response. The underlying physics is that the appearance of resonance states as well as the broadening of the bands leads to a more complicated selection rule for the optical transitions, making it possible to excite new electron-hole pairs in the forbidden region. These features in optical conductivity provide valuable information to understand the impurity behaviors in 3D Dirac materials.     

极紫外波段Ar光谱分析在EAST偏滤器杂质屏蔽效应研究中的应用

在托卡马克偏滤器区域充入杂质气体是检验偏滤器杂质屏蔽效应的重要手段。利用快速极紫外EUV光谱仪对EAST托克马克装置上开展的偏滤器Ar杂质注入实验进行观测。结合NIST原子光谱数据库对2～50 nm范围内不同电离态Ar的线光谱进行了谱线识别,识别出Ar Ⅳ,Ar Ⅸ-Ⅺ,Ar ⅩⅣ-ⅩⅥ等若干个电离态的谱线。为了同时观测等离子体不同区域的Ar杂质行为,在杂质注入实验时重点监测Ar ⅩⅥ35.39 nm(Ar ⅩⅥ电离能918.4 eV,主要分布在等离子体芯部)和Ar Ⅳ44.22 nm(Ar Ⅳ电离能9.6 eV,主要分布在等离子体边界)这两条谱线。利用该两条谱线强度随时间演化的结果初步分析了偏滤器杂质屏蔽效应。在同一充气口不同等离子体位形下的实验结果表明偏滤器对于从偏滤器区域注入Ar杂质的屏蔽效果优于从主等离子体区域注入,并且下偏滤器及内冷泵的综合粒子排除能力优于上偏滤器。