偏滤器运行模式对托卡马克边缘区等离子体平行流的影响

我们使用一维流体模型,根据在不同偏滤器运行模式下静压强沿着磁力线方向的分布变化,讨论了偏滤器运行模式对托卡马克边缘区等离子体平行流的影响.低再循环模式下,静压强从X点 (X-point)附近的刮削层区域开始明显下降,变化趋势与密度变化趋势一致;等离子体平行流的马赫数在偏滤器区域逐步变大,变化从平缓到迅速.高再循环模式下,静压强在靶板附近的区域迅速下降,在其他区域变化非常小;等离子体平行流的马赫数仅在靠近靶板附近的区域迅速变大,在其他区域变化平缓.在弱脱靶模式下的静压强变化与高再循环模式下类似,不过静压强在X-point附近的刮削层区域开始出现下降的趋势,导致等离子体平行流的马赫数在X-point处的值比在高再循环模式下大.强脱靶模式下,静压强在刮削层区域开始明显下降,在远离靶板的偏滤器区域,静压强迅速下降的地方,观察到高马赫数等离子体平行流.静压强迅速下降引起动压强迅速上升来维持总的压强守恒是在强脱靶状态 下产生高马赫数平行流的一种可能驱动机理.     

Treatment of advanced divertor configurations in the flux-coordinate independent turbulence code GRILLIX

Advanced divertor configurations modify the magnetic geometry of the divertor to achieve a combination of strong magnetic flux expansion, increased connection length and higher divertor volume—to improve detachment stability, neutral/impurity confinement and heat-channel broadening. In this paper, we discuss the modification of the flux-coordinate independent (FCI) turbulence code GRILLIX to treat generalized magnetic geometry, to allow for the investigation of the effect of magnetic geometry on turbulent structures in the edge and scrape-off layer (SOL). The development of grids and parallel operators from numerically defined magnetic equilibria is discussed, as is the application of boundary conditions via penalization, with the finite-width method generalized to treat complex non-conformal boundaries. Initial testing of hyperbolic (advection) and parabolic (diffusion) test cases are presented for the Snowflake scenario.     

Modeling ExB drift transport in conceptual slot divertor configurations

At DIII-D, a slot divertor concept, called small-angle-slot (SAS), is under development, aiming to enable detachment at relatively low plasma edge density. We report on simulations using the SOLPS-ITER two-dimensional edge code to examine the performance of conceptual “SAS 2” slot configurations. The focus of the analysis is on E  ×  B drift effects on upstream density at detachment (UDD), with detachment marked by electron temperature T_e ≤ 3 eV at the outer strike point (OSP). With toroidal field such that radial E  ×  B drift carries particles from the OSP towards the private flux region (PFR), placing the OSP near the inner slot wall gives ≈20% lower UDD than having the OSP near the outer wall. The inner wall effectively traps the radial E  ×  B drift flux, resulting in low T_e and associated radial electric field in the PFR, and thus small losses from the slot to the inner target via poloidal E  ×  B drift flux. With toroidal field reversed such that radial E  ×  B drift is reversed, OSP placement near the inner wall gives ≈10% lower UDD than OSP placement near the outer wall. Although radial E  ×  B flux is from the OSP towards the outer wall, this flux largely escapes the slot, raising the UDD. A change in the slot shaping is suggested with the goal of eliminating such E  ×  B -driven particle losses from the slot.     

Molecular contribution to the Dα emission in the divertor of the ASDEX Upgrade experiment

Spectral line emission from the deuterium Balmer α line and from molecular deuterium in the Fulcher band, d³Π_u→a³∑_g⁺, was studied in the outer divertor region of the ASDEX Upgrade plasma with a pair of relatively calibrated spectrometers. A dependence of the signals on the proximity of the plasma strike point and on divertor gas puffing was noted. The rotational spectrum of the lowest diagonal vibrational molecular bands indicated rotational temperatures of ca. 1000 K and hence, through calculation of relative upper state populations, a ground state vibrational temperature of ca. 4000 K. Calculating the particle fluxes, the molecular deuterium was found to contribute up to 1% of the Dα intensity, the relative importance of the molecules at some divertor heights was affected by the position of the strike point.     

偏滤器等离子体中杂质对钨壁材料的侵蚀模拟研究

偏滤器是托卡马克中与等离子体直接接触的部件,为了保证装置的寿命,需要尽可能地减小等离子体对偏滤器靶板的侵蚀.本文用粒子模拟的方法研究了不同等离子体温度情况下碳和铍两种杂质离子对钨偏滤器侵蚀速率的影响.模拟首先得到稳定的鞘层结构、入射到靶板的离子流和能流密度,并通过统计获得了入射离子的能量和角度分布,最终根据这些物理参量,采用经验公式计算出钨靶板的侵蚀速率.研究表明,在等离子体温度不太高的情况下,钨靶板的热侵蚀几乎不起作用,而由于杂质离子对钨的物理溅射阈值较低,并且会通过鞘层加速获得能量,因此其对钨壁材料的物理溅射是导致靶板侵蚀的主要原因,另外靶板材料的侵蚀速率随着等离子体温度升高以及杂质含量增大而急剧增大.     

Impact of fast vertical and radial plasma movement on type-I ELMs in ASDEX upgrade

For the ITER project it is clear that steps have to be taken in order to avoid or mitigate type-I ELMs when operating in the standard H-mode scenario. Otherwise, divertor power loads induced by intrinsic ELMs will result in an intolerably short divertor life time. Amongst others, “magnetic triggering” based on a fast vertical movement of the plasma column has proven its ability to achieve ELM frequency control and hence mitigation by locking the ELM frequency to the imposed motion. Here, we report on an attempt to widen this approach by applying a cyclic radial plasma shift. Although motional cycle amplitudes sufficient for ELM frequency locking were achieved even easier than in the vertical case, no ELM control was established for the radial case. Analysis of this different behaviour can allow for better insight into underlying ELM release mechanisms and might potentially be a useful tool for mapping out ELM stability boundaries. Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Roma, Italy, June 26–27, 2006.     

Influence of the inverse sheath on divertor plasma performance in tokamak edge plasma simulations

Recently, it was shown that strong electron thermionic emission from material walls could result in the formation of an “inverse sheath,” which prevents the flow of cold ions to the wall.^[1–3] Such regimes look very favourably from the point of view of plasma–material interactions at the edge of magnetic fusion devices, where the problem of the erosion of plasma-facing components under ion irradiation is one of the key issues for the development of future magnetic fusion reactors. However, it is not clear whether such regimes are compatible with edge plasma parameters and heat removal requirements in fusion reactors. To address the issue of practicality of the “inverse sheath” regime for edge tokamak plasma conditions, we perform a set of numerical simulations with 2D edge plasma transport code UEDGE^[4] for a DIII-D-like geometry and magnetic configuration. To describe both “standard” and “inverse sheath” conditions within the framework of the UEDGE code (which does not consider the sheath region per se), at the material surfaces, we apply effective boundary conditions that emulate both “standard” and “inverse sheath” regimes. We demonstrate that, for the same input parameters, spatial distributions of edge plasma parameters corresponding to detached divertor and “inverse sheath” regimes are similar, with only a few minor differences. We discuss the compatibility of “inverse sheath” regimes with core plasma parameters.     

Observation of poloidal current flowed to the vessel after failure of vertical position feedback control in EAST Tokamak

Plasmas with vertically elongated cross-sections tend to be unstable to an axis-symmetric instability. This paper studies the magnetohydrodynamic equilibria in elongated plasmas after failure of vertical feedback control by using magnetic data for EAST device. Vertical forces on the vessel due to the induced polodial and toroidal currents are evaluated. The maximum force of the Fz_pol in vertical displacement events for EAST designed parameters is given.     

Numerical analysis of high Mach flow and flow reversal in the experimental advanced superconducting tokamak divertor

The B2-Eirene (SOLPS 4.0) code package is used to investigate the plasma parallel flow, i.e., the scrape-off layer (SOL) flow, in the experimental advanced superconducting tokamak (EAST) divertor. Simulation results show that the SOL flow in the divertor region can exhibit complex behaviour, such as a high Mach flow and flow reversal in different plasma regimes. When the divertor plasma is in the detachment state, the high Mach flow with approaching or exceeding sonic speed is observed away from the target plate in our simulation. When the divertor plasma is in the high recycling state, the flow reversal with a small Mach number (|M|< 0.2) is observed near the X-point along the separatrix region. The driving mechanisms for the high Mach flow and the reversed flow are analysed theoretically through momentum and continuity equations, respectively. The profile of the ionization sources is shown to be a possible formation condition causing the complex behaviour of the SOL flow. In addition, the effects of the high Mach flow and the flow reversal on the impurity transport are also discussed in this paper.     

经典漂移对EAST钨杂质产生和输运特性影响的模拟研究

本文采用蒙特卡罗杂质输运程序DIVIMP,针对先进实验超导托卡马克(EAST)的上单零位形放电,模拟研究了不同漂移情况下(无漂移、离子BíB漂移向下/上)的钨杂质产生和输运特性。结果表明,经典漂移显著影响了钨杂质自偏滤器靶板的溅射通量及其在上游区域的含量。     

HL-2A装置偏滤器室中性气体压强的初步研究

HL-2A装置上首次实现了偏滤器位形放电。采用专门研制的可在强磁场和强噪声环境下工作的快响应真空电离规对偏滤器室内的中性气体压强进行了测量,给出了HL-2A装置偏滤器有关结构的基础数据。初步研究了偏滤器位形和孔栏位形放电期间偏滤器室中性气体压强的特性。     

Effects of some parameters on the divertor plasma sheath characteristics and fuel retention in castellated tungsten tile gaps

Castellation of plasma facing components is foreseen as the best solution for ensuring the lifetime of future fusion devices. However, the gaps between the resulting surface elements can increase fuel retention and complicate fuel removal issues. To know how the fuel is retained inside the gaps, the plasma sheath around the gaps needs to be understood first. In this work, a kinetic model is used to study plasma characteristics around the divertor gaps with the focus on the H＋ penetration depth inside the poloidal gaps, and a rate-theory model is coupled to simulate the hydrogen retention inside the tungsten gaps. By varying the magnetic field strength and plasma temperature, we find that the H＋ cyclotron radius has a significant effect on the penetration depth. Besides, the increase of magnetic field inclination angle can also increase the penetration depth. It is found in this work that parameters as well as the penetration depth strongly affect fuel retention in tungsten gaps.     

HL-2M常规偏滤器位形抽气对碳杂质分布影响的模拟分析

在小角度V型结构的HL-2M常规偏滤器位形下,采用SOLPS 5.0程序研究了抽气速率Sp对装置粒子排除控制能力及溅射产生的碳杂质分布的影响.模拟结果表明,当进入边缘区域的能量为4MW、上游密度为n sep=3.0×10 m-3时,过高的抽气速率(大于40m3?s-1)将迅速降低靶板附近中性粒子压强和等离子体密度,并引...     

Universal behavior of the upper critical field in iron-based superconductors

The newly discovered iron-based high temperature superconductors have demonstrated rich physical properties. Here we give a brief review on the recent studies of the upper critical field and its anisotropy in a few typical series of the iron-based superconductors (FeSCs). In spite of their characters of a layered crystal structure, all the FeSCs possess an extremely large upper critical field and a weak anisotropy of superconductivity, being unique among the layered superconductors. These particular properties indicate potential applications of the FeSCs in the future. Based on the experimental facts of the FeSCs, we will discuss the possible mechanisms of pair breaking in high magnetic fields and its restrictions on the theoretical analysis of the superconducting pairing mechanisms.     

Homoclinic tangle of the primary separatrix in the compact and closed versus open and unbounded magnetic topologies for divertor tokamaks

The simple map and the symmetric quartic map are the generic representation of the open-unbounded and closed-compact magnetic topologies for single-null divertor tokamaks, respectively. The map parameter represents the magnetic asymmetries. The two maps are used to calculate the homoclinic tangles in the two topologies in divertor tokamaks. It is found that as the magnetic asymmetries become larger, the homoclinic tangle of the simple map becomes extremely elongated radially as opposed to the homoclinic tangle of the symmetric quartic map which becomes wider poloidally.     

Effect of time delay on the upper bound of the time derivative of information entropy in a stochastic dynamical system

The effects of the time delay on the upper bound of the time derivative of information entropy are investigated in a time-delayed dynamical system driven by correlated noise. Using the Markov approximation of the stochastic delay differential equations and the Schwartz inequality principle, we obtain an analytical expression for the upper bound U_B(t) of the time derivative of the information entropy. The results show that there is a critical value of τ (delay time), and U_B(t) presents opposite behaviours on difference sides of the critical value. For the case of the weak additive noise, τ can induce a reentrance transition. Delay time τ also causes a reversal behaviour in U_B(t)-λ plot, where λ denotes the degree of the correlation between the two noises.     

Strong Pauli paramagnetic effect in the upper critical field of KCa2Fe4As4F2

Recently, 12442 system of Fe-based superconductors has attracted considerable attention owing to its unique double-Fe As-layer structure. A steep increase in the in-plane upper critical field with cooling has been observed near the superconducting transition temperature, Tc, in KCa2Fe4As4F2 single crystals. Herein, we report a high-field investigation on upper critical field of this material over a wide temperature range, and both out-of-plane(H∥c, Hc2c) and in-plane(H∥ab, Hc2ab ) directions have been measured.A sublinear temperature-dependent behavior is observed for the out-of-plane Hc2c , whereas strong convex curvature with cooling is observed for the in-plane Hc2ab . Such behaviors could not be described by the conventional Werthamer-Helfand-Hohenberg(WHH) model. The data analysis based on the WHH model by considering the spin aspects reveals a large Maki parameter α=9,indicating that the in-plane upper critical field is affected by a very strong Pauli paramagnetic effect.     

非欧姆注入单层有机发光器件低场下电流传导温度特性的数值研究

温度是影响有机发光器件特性的一个重要因素,考虑了电流的注入限制和体限制之后,运用数值方法,研究了在低电场下温度对单层有机发光器件的J-V特性以及电场和载流子在有机层中的分布的影响。结果表明,在一定电压下,温度升高时,器件电流增大,有机层中载流子及其梯度分布增大,电场强度分布梯度也增大。并且当温度逐渐升高时,器件的电流传导将趋向于体限制,而当温度逐渐降低时,器件电流传导将趋向于注入限制,此时有机层内各处电场强度趋于均匀。并且结果表明,数值结果与实验结果符合得比较好。     

Anisotropy of the upper critical field in c-axis oriented MgB2 thin films

C-axis oriented MgB_2 thin films were synthesized on single-crystal MgO (111) substrates using a chemical vapour deposition technique. The as-formed films revealed a sharp superconducting transition temperature of 38K with the transition width 0.2K. The temperature dependence of the upper critical magnetic field H_{c2}(T) in the films was determined via resistivity for magnetic field H parallel and perpendicular to the c axis of the films. Using the Werthamer－Helfand－Hohenberg formula, we obtained the anisotropy ratio of the upper critical field γ=1.2.     

Spatiotemporal patterns of stable isotopes and hydrochemistry in springs and river flow of the upper Karkheh River Basin,Iran

Karst springs of the Zagros Mountains contribute a significant amount to agricultural and human water demands of western and south-western Iran. For an adequate management of available water resources in semi-arid and arid regions, sufficient hydrological monitoring is needed, and hydro-chemical and isotope hydrological data provide important additional information. About 350 water samples were collected from precipitation, river water, and karst springs of the upper part of the Karkheh River Basin (20,895 km²) located between 33°35^′ and 34°55^′ North and 46°22^′ and 49°10^′ East with elevations ranging from 928 to 3563 m above sea level. Sampling was conducted in monthly time resolution from August 2011 to July 2012. All samples were analysed for hydro-chemical parameters (pH, electrical conductivity, and major ions) and stable isotopes (deuterium, oxygen-18). Isotope values of precipitation indicate a local meteoric water line (Zagros MWL δ²H=6.8 δ¹⁸O+10.1; R²=0.99) situated between the Mediterranean MWL and Global MWL. Spring and river water isotope values vary between?7.1 and?4.1 ‰, and?38 and?25 ‰ for δ¹⁸O and δ²H, respectively, responding to winter snowmelt and evaporation. This work implements stable isotopes and hydro-chemical information of springs and river water to understand hydrological and hydro-geological interrelations in karstic semi-arid areas and helps to improve the current water resources management practices of western Iran.