长脉冲等离子体放电下HT-7装置限制器温度变化及能流分析

 在HT-7托卡马克等离子体长脉冲放电过程中，作为直接面对等离子体的第一壁限制器表面的温度变化及其承受的能流密度的计算，对于判断限制器的作用和对等离子体的影响都有非常重要的意义。主要从测量到的距离限制器表面3mm处温度变化曲线,采用无限大平面模型计算限制器模头表面能量沉积的能流密度,并讨论了不同等离子体放电下局部点能流密度的差别。多数长脉冲放电下，少数局部点的温升超过1 000℃，最大能流密度超过10MW/m ²；但通过对等离子体位移的控制，局部点温升被抑制，高密度能流持续时间短，有利于长脉冲放电。同时对限制器结构和材料对模头温度的影响也做了比较详细的分析。     

Electrostatic Fluxes and Plasma Rotation in the Edge Region of EXTRAP-T2R

The EXTRAP-T2 reversed field pinch has undergone a significant reconstruction into the new T2R device. This paper reports the first measurements performed with Langmuir probes in the edge region of EXTRAP-T2R. The radial profiles of plasma parameters like electron density and temperature, plasma potential, electrical fields and electrostatic turbulence-driven particle flux are presented. These profiles are interpreted in a momentum balance model where finite Larmor radius losses occur over a distance of about two Larmor radii from the limiter position. The double shear layer of the E×B drift velocity is discussed in terms of the Biglari-Diamond-Terry theory of turbulence decorrelation.     

A Brinkman penalization method for compressible flows in complex geometries

To simulate flows around solid obstacles of complex geometries, various immersed boundary methods had been developed. Their main advantage is the efficient implementation for stationary or moving solid boundaries of arbitrary complexity on fixed non-body conformal Cartesian grids. The Brinkman penalization method was proposed for incompressible viscous flows by penalizing the momentum equations. Its main idea is to model solid obstacles as porous media with porosity, ϕ, and viscous permeability approaching zero. It has the pronounced advantages of mathematical proof of error bound, strong convergence, and ease of numerical implementation with the volume penalization technique. In this paper, it is extended to compressible flows. The straightforward extension of penalizing momentum and energy equations using Brinkman penalization with respective normalized viscous, η, and thermal, η_T, permeabilities produces unsatisfactory results, mostly due to nonphysical wave transmissions into obstacles, resulting in considerable energy and mass losses in reflected waves. The objective of this paper is to extend the Brinkman penalization technique to compressible flows based on a physically sound mathematical model for compressible flows through porous media. In addition to penalizing momentum and energy equations, the continuity equation for porous media is considered inside obstacles. In this model, the penalized porous region acts as a high impedance medium, resulting in negligible wave transmissions. The asymptotic analysis reveals that the proposed Brinkman penalization technique results in the amplitude and phase errors of order O((ηϕ)^1/2) and O((η/η_T)^1/4ϕ^3/4), when the boundary layer within the porous media is respectively resolved or unresolved. The proposed method is tested using 1- and 2-D benchmark problems. The results of direct numerical simulation are in excellent agreement with the analytical solutions. The numerical simulations verify the accuracy and convergence rates.     

Modelling of particle flows in a scrape-off layer with limiter biasing

The superconducting tokamak Tore Supra will be equipped with an actively cooled toroidal pump limiter (TPL), in the framework of the CIEL (Composants Internes Et Limiteurs) project, dedicated to plasma facing component design for steady state operation. The TPL is equipped with throats, located only on the high field side, for particle collection allowing the control of plasma density which is essential for long plasma discharges. The present design work of the CIEL includes a biasing system in order to enhance the particle pumping. A fluid model, based on the classical fluid equation, is used to estimate the effects of the electric field on the particle flows in the Scrape-Off Layer (SOL). The modifications of the density, the particle flow (toroidal and poloidal) and the position of the stagnation point are discussed as a function of the bias voltage. The model clearly illustrates the different resulting effects on particle pumping for a divertor and a limiter configuration which are designed respectively for poloidal or parallel particle collection. The model is used to interpret the ALT-biasing experiments recently carried out on TEXTOR-94. The pumping capability is shown to be improved by about (15–20)% for positive biasing while the experimental measurements of parallel Mach number are reproduced as a function of the applied voltage. The e-folding length of the edge density in the SOL is also shown to increase from 1.5 to about 2.0 cm for a biased voltage of −400 to 400 V, respectively, in accordance with the model. Finally, the model is used to extrapolate the TEXTOR-94 results to CIEL suggesting that pumping speed enhancement of 25 to 30% may be obtained. Partner in Trilateral Euregio Cluster Partner in Trilateral Euregio Cluster Presented at the Workshop on Role of Electric Fields in Plasma Confinement and Exhaust, Budapest, 18–19 June 2000.     

A Fourier spectral method for the Navier–Stokes equations with volume penalization for moving solid obstacles

An efficient numerical scheme to compute flows past rigid solid bodies moving through viscous incompressible fluid is presented. Solid obstacles of arbitrary shape are taken into account using the volume penalization method to impose no-slip boundary condition. The 2D Navier–Stokes equations, written in the vorticity-streamfunction formulation, are discretized using a Fourier pseudo-spectral scheme. Four different time discretization schemes of the penalization term are proposed and compared. The originality of the present work lies in the implementation of time-dependent penalization, which makes the above method capable of solving problems where the obstacle follows an arbitrary motion. Fluid–solid coupling for freely falling bodies is also implemented. The numerical method is validated for different test cases: the flow past a cylinder, Couette flow between rotating cylinders, sedimentation of a cylinder and a falling leaf with elliptical shape.     

Multigrid Solution of the Incompressible Navier–Stokes Equations for Density-Stratified Flow past Three-Dimensional Obstacles

The steady incompressible Navier–Stokes equations in three dimensions are solved for neutral and stably stratified flow past three-dimensional obstacles of increasing spanwise width. The continuous equations are approximated using a finite volume discretisation on staggered grids with a flux-limited monotonic scheme for the advective terms. The discrete equations which arise are solved using a nonlinear multigrid algorithm with up to four grid levels using the SIMPLE pressure correction method as smoother. When at its most effective the multigrid algorithm is demonstrated to yield convergence rates which are independent of the grid density. However, it is found that the asymptotic convergence rate depends on the choice of the limiter used for the advective terms of the density equation, and some commonly used schemes are investigated. The variation with obstacle width of the influence of the stratification on the flow field is described and the results of the three-dimensional computations are compared with those of the corresponding computation of flow over a two-dimensional obstacle (of effectively infinite width). Also given are the results of time-dependent computations for three-dimensional flows under conditions of strong static stability when lee-wave propagation is present and the multigrid algorithm is used to compute the flow at each time step.     

Analysis of the Limiter Material Erosion in T-3M Tokamak

The limiter material erosion dynamics under disruption instability in T-3M tokamak was studied. Erosion mechanisms of graphite (uglesitall) and boron nitride were examined. It was shown that the erosion of the limiter arises not only at the moment of disruption, but also before it, when the MHD perturbations of plasma column emerge. We had evidence of the superthermal electrons playing a significant role in the limiter erosion. The erosion decreases with the plasma density rising above the threshold value.     

Modeling of electrical confined-capillary-discharge where the discharge zone is extended by an additional pipe

Plasma injectors are a source of pulsed, high momentum and temperature fluid. This fluid can serve as a very efficient reactive mixing and accelerating agent in several applications including chemical waste decomposition and hard materials coating. It can also serve as an efficient medium for synthesis of nano-particles and their deposition on various substrates. In those applications tuning the momentum and the thermodynamic properties of the plasma jet is of paramount importance as the quality of the interaction strongly depends on them. This Letter proposes a method and a model that will allow additional tuning to the thermodynamic properties of the plasma jet by adding an extension to the discharge zone. A steady state model of processes taking place in a realistic confined capillary discharge system is presented. A comparison between this system and the parameters characterizing a discharge in a “conventional” ablative system is presented. The results obtained indicate that the non-discharge zone may provide an additional degree of freedom to optimize the system's performance. It enhances the control of the plasma parameters that allows optimal and predictable momentum control over the plasma jet. The theoretical predictions for the plasma parameters agree well with experimentally obtained data.     

平行轨道加速器等离子体动力学特性研究

等离子体电磁加速器可产生高速度、高密度等离子体射流而广泛应用于核物理、天体物理等领域.本文通过光电二极管、磁探头研究了不同放电电流和初始气压条件下等离子体在平行轨道加速器内的轴向运动特性.通过电流截断的方法,采用冲击摆测量了首次等离子体射流的动量.平行轨道加速器驱动电源由14级脉冲形成网络组成,每级电容为1.5μF,每级电感约为300 nH,得到振荡衰减型方波的电流波形.实验发现,电流过零时,轨道起始处一般会发生二次击穿,并形成二次轴向运动的等离子体.放电电流为10—55 kA、初始气压为200—1000 Pa时,等离子体的轴向速度为8—25 km/s.实验获得的等离子体的运动速度为雪犁模型理论结果的60%—80%,这主要是理论模型忽略了电极表面对电弧的黏滞阻力以及电极烧蚀引起的质量增加.等离子体动量与电流的平方随时间的积分成正比.放电电流为21-51.6 kA时,首次等离子体射流的动量为1.49—9.88 g·m/s.等离子体运动过程中除了受到洛伦兹力外,还会受到电极表面的黏滞阻力,造成等离子体动量约为理论结果的75%.     

A Brinkman penalization method for compressible flows in complex geometries

To simulate flows around solid obstacles of complex geometries, various immersed boundary methods had been developed. Their main advantage is the efficient implementation for stationary or moving solid boundaries of arbitrary complexity on fixed non-body conformal Cartesian grids. The Brinkman penalization method was proposed for incompressible viscous flows by penalizing the momentum equations. Its main idea is to model solid obstacles as porous media with porosity, , and viscous permeability approaching zero. It has the pronounced advantages of mathematical proof of error bound, strong convergence, and ease of numerical implementation with the volume penalization technique. In this paper, it is extended to compressible flows. The straightforward extension of penalizing momentum and energy equations using Brinkman penalization with respective normalized viscous, η, and thermal, η_T, permeabilities produces unsatisfactory results, mostly due to nonphysical wave transmissions into obstacles, resulting in considerable energy and mass losses in reflected waves. The objective of this paper is to extend the Brinkman penalization technique to compressible flows based on a physically sound mathematical model for compressible flows through porous media. In addition to penalizing momentum and energy equations, the continuity equation for porous media is considered inside obstacles. In this model, the penalized porous region acts as a high impedance medium, resulting in negligible wave transmissions. The asymptotic analysis reveals that the proposed Brinkman penalization technique results in the amplitude and phase errors of order O((η)^1/2) and O((η/η_T)^1/43/4), when the boundary layer within the porous media is respectively resolved or unresolved. The proposed method is tested using 1- and 2-D benchmark problems. The results of direct numerical simulation are in excellent agreement with the analytical solutions. The numerical simulations verify the accuracy and convergence rates.     

First results of movable limiter experiments and its effects on the tokamak plasma confinement

Limiters play a number of roles in the tokamak operation. It serves primarily to protect the wall from the plasma when there are disruptions, runaway electrons, or other instabilities and also the limiters localize the plasma–surface interaction. In this research, we presented the first results of movable limiter experiments and its effects on the tokamak plasma confinement. For this purpose, we designed, constructed, and installed a movable localized poloidal limiter, and then measured the effects of limiter position on the time intervals of plasma parameters such as plasma density, temperature, and energy confinement time. The results of effects of the movable limiter experiments on plasma confinement.     

Ion velocity distribution function investigated inside an unstable magnetized plasma exhibiting a rotating nonlinear structure

The frequent situation where a strongly nonlinear rotating structure develops in a linear magnetized plasma column is investigated experimentally with emphasis on the ion velocity distribution function (IVDF). Most often, a mode m=2 appears exhibiting a large density and potential perturbation with angular frequency slightly above the ion cyclotron frequency. For the first time the spatiotemporal evolution of the IVDF is studied using time-resolved laser induced fluorescence to explore the ion's interaction with the nonlinear wave propagating inside the column and at the origin of plasma transport outside the limiter. The ion fluid exhibits an alternance from azimuthal to radial velocity due to the electric field inside the rotating structure. A fluid model also allows us to locally reconstruct the self-consistent electric field evolution which contradicts all existing theories.     

HL—1装置等离子体粒子平衡的光谱研究

本文描述HL-1装置器壁碳化,观察了碳化前后氢的约束时间和再循环现象,同时还观察了加抽气孔栏条件下粒子约束时间和再循环的变化。实验表明,碳化后氢的再循环增大,使用抽气孔栏可以控制壁附近边缘等离子体的粒子密度,粒子约束时间比不用抽气孔栏增大17.7％,再循环系数减小13.2％。     

HL-2M 装置限制器系统设计及工艺研究

HL-2M 装置设计有 8 套固定极向限制器和 1 套活动极向限制器,其主要功能是进一步加强保护真空 室及其内部件,同时活动限制器还将提供不同孔栏位形用于等离子体物理实验。根据 HL-2M 装置总体运行需求, 活动限制器结构设计可移动有效距离为 120mm,活动限制器移动精度可控制在±0.1mm 以内。基于激光跟踪仪测 量方法对 HL-2M 装置限制器系统完成了高精度的安装,限制器的面向等离子体关键位置安装精度优于±0.5mm, 通过初始等离子体放电实验表明其运行状态均正常。      

Design and construction of hot limiter biasing system for the tokamak

A hot limiter biasing system with a simplified fast switch circuit was designed, constructed, and installed on the IR-T1 tokamak, and then the negative voltage applied to a hot limiter inserted inside the tokamak fixed limiter and the plasma current, poloidal, and radial components of the magnetic fields, loop voltage, diamagnetic flux, and the ion saturation currents in the absence and presence of the biased limiter were measured. Results of measurements of biasing effects on the plasma equilibrium behavior and edge plasma rotation are compared and discussed.     

Temperature Effects on the Beat Heating of a Collisional Magnetoplasma

The beat heating of a magneto-plasma by two antiparallel electromagnetic waves at different temperatures is examined. The effects of plasma temperature, plasma electron collisions, plasma ion collisions and magnitude and direction of the magnetic field on the excitation of plasma electron waves and plasma ion waves are studied. A formula for the power absorption density of the plasma by using Maxwell's equations in conjuction with continuity and momentum equation. including collisions and pressure tensor terms, is derived. The contribution of the plasma temperature to the power absorption density, both at low and high beat frequencies, of the collisional and the non-collisional magnetised plasmas is found very significant and is illustrated numerically. The inclusion of pressure tensor term in the momentum equation is also found to cause characteristic changes in the power absorption density of the plasma with the orientation of magnetic field.     

Dynamic interaction of plasma flow with the hot boundary layer of a geomagnetic trap

The study of the interaction between collisionless plasma flow and stagnant plasma revealed the presence of an outer boundary layer at the border of a geomagnetic trap, where the super-Alfvén subsonic laminar flow changes over to the dynamic regime characterized by the formation of accelerated magnetosonic jets and decelerated Alfvén flows with characteristic relaxation times of 10–20 min. The nonlinear interaction of fluctuations in the initial flow with the waves reflected from an obstacle explains the observed flow chaotization. The Cherenkov resonance of the magnetosonic jet with the fluctuation beats between the boundary layer and the incoming flow is the possible mechanism of its formation. In the flow reference system, the incoming particles are accelerated by the electric fields at the border of boundary layer that arise self-consistently as a result of the preceding wave-particle interactions; the inertial drift of the incoming ions in a transverse electric field increasing toward the border explains quantitatively the observed ion acceleration. The magnetosonic jets may carry away downstream up to a half of the unperturbed flow momentum, and their dynamic pressure is an order of magnitude higher than the magnetic pressure at the obstacle border. The appearance of nonequilibrium jets and the boundary-layer fluctuations are synchronized by the magnetosonic oscillations of the incoming flow at frequencies of 1–2 mHz.     

激光辐照固体靶产生等离子体反冲研究

提出一种通过诊断等离子体反冲动量来计算激光加载产生冲击压强的方法. 当强激光辐照固体靶表面时, 所产生的高速喷射的等离子体对靶具有反冲作用, 通过诊断等离子体反冲动量的变化可以计算激光辐照固体靶产生的冲击压强变化. 本文利用辐射流体力学软件研究了这种诊断方法, 模拟采用的激光功率密度为5×10¹²-5×10¹³ W/cm², 激光脉宽选取纳秒量级. 模拟结果表明该方法是有效且可行的.     

SALE速度重映算法的改进

在一维交错网格上基于SALE算法的速度重映策略,提出了3种动量通量的改进算法:①采用迎风斜率加修补的SUR目的;②采用minmod斜率限制器的SM目的和③采用一种新的斜率限制器加修补的SLR目的.3种目的具有二阶守恒保界的性质,同时继承了SALE算法简单高效的特点,可以直接推广到二维情况.     

One-Dimensional Transport Code Modeling of the Divertor-Limiter Region in Tokamaks

A model of the divertor-limiter scrapeoff region has been incorporated into the BALDUR one-dimensional tokamak transport code. Simulations of the proposed Toroidal Fusion Test Reactor (TFTR), and Poloidal Divertor (PDX) experiments and existing Alcator-A tokamak experiments have been carried out for ohmic and neutral beam heated cases. In particular, we have studied how the edge conditions and energy-loss mechanisms in PDX depend upon plasma density, and compared our results with analytic estimates. The sensitivity of the results to changes in the transport coefficients and scrapeoff model is discussed with particular reference to the power loading on the TFTR limiter.