HT—6M闭环反馈平衡控制系统

本文描述HT-6M托卡马克装置闭环反馈平衡控制系统的结构组成,通过对各个环节的简化,得到了有效实用的数学模型,进而分析了系统稳态和动态性能。实验结果表明,该系统运行可靠;并且,将等离子体环水平位移控制在2mm以内。     

非圆截面托卡马克轴对称模的反馈稳定

通过直接解真空区扰动磁面的边值问题,本文解析地研究了非闭合导壳对托卡马克中轴对称MHD模的反馈稳定性。我们取等离子体截面为椭圆,反馈系统由导壳和主动反馈线圈构成。结果表明,两块放在等离子体上下的导体块有很强的稳定作用;电阻壳可用以抑制高频模式,主动反馈线圈可用以稳定低频模式。 关键词：     

A simple model for fast correction of the horizontal position of atokamak plasma

A virtual movement of the plasma in the radial direction was studied in order to obtain the magnitude of the vertical field applied to the Tokamak de Varennes plasma for fast horizontal motion using coils inside the vacuum vessel. The developed model includes the radial dependence of several parameters     

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为进一步提高HL-2A装置的放电参数和优化等离子体位形，给出了三种可能的主机改造途径：保留真空室，去掉并调整真空室内部分多极场线圈的局部改造方案；保留真空室，重新布局极向场线圈的中等规模改造方案；重新设计真空室和极向场线圈系统的大规模改造方案。对三种改造方案对放电参数和位形的影响和改造工程的可行性进行了分析比较，重新设计真空室和极向场线圈系统的大规模改造方案是最佳选择。     

A method for calculating active feedback system to provide vertical position control of plasma in a tokamak

In designing tokamaks, the maintenance of vertical stability of plasma is one of the most important problems. Systems of the passive and active feedbacks are applied for this purpose. Role of the passive system consisting of a vacuum vessel and passive coils is to suppress fast MHD (magnetohydrodynamic) instabilities. The active feedback system is applied to control slow motions of plasma. The objective of the paper is to investigate two successive problems, solution of which allows to determine the possibility of controlling plasm a motions. One of these is the problem of vertical stability under the assumption of ideal conductivity of plasma and passive stabilizing elements. The problem is solved analytically and on the basis of the obtained solution a criterion of MHD-stability is formulated. The other problem is connected with the control of plasma vertical position with active feedback system. Calculation of feedback control parameters is formulated as an optimization problem and an approximate method to solve the problem is suggested. Numerical simulations are performed with parameters of the T-15M tokamak in order to justify the suggested method.      

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破裂诱发的Halo电流会流进内真空室结构,对偏滤器支撑结构有较大的破坏。通过安装在偏滤器支撑结构上的罗柯夫斯基线圈对EAST中Halo电流进行了研究。通过分析不同位置的Halo电流信号,发现这些Halo电流具有环向不对称性,环向不对称因子为2.5, 的最大值是0.65。这些结果对EAST真空室电磁载荷分析有着重要的意义。     

Study of Globus-M Tokamak Poloidal System and Plasma Position Control

In order to provide efficient performance of tokamaks with vertically elongated plasma position, control systems for limited and diverted plasma configuration are required. The accuracy, stability, speed of response, and reliability of plasma position control as well as plasma shape and current control depend on the performance of the control system. Therefore, the problem of the development of such systems is an important and actual task in modern tokamaks. In this study, the measured signals from the magnetic loops and Rogowski coils are used to reconstruct the plasma equilibrium, for which linear models in small deviations are constructed. We apply methods of the H∞-optimization theory to the synthesize control system for vertical and horizontal position of plasma capable to working with structural uncertainty of the models of the plant. These systems are applied to the plasma-physical DINA code which is configured for the tokamak Globus-M plasma. The testing of the developed systems applied to the DINA code with Heaviside step functions have revealed the complex dynamics of plasma magnetic configurations. Being close to the bifurcation point in the parameter space of unstable plasma has made it possible to detect an abrupt change in the X-point position from the top to the bottom and vice versa. Development of the methods for reconstruction of plasma magnetic configurations and experience in designing plasma control systems with feedback for tokamaks provided an opportunity to synthesize new digital controllers for plasma vertical and horizontal position stabilization. It also allowed us to test the synthesized digital controllers in the closed loop of the control system with the DINA code as a nonlinear model of plasma.     

Optimization and performance of a high-speed plasma position digital control system

This paper addresses optimization of a high-speed digital feedback controller for a plasma position in Damavand tokamak. Damavand tokamak discharges have plasma currents up to 40 kA with discharge duration greater than 15 ms and toroidal magnetic fields up to 1.2 T. The plasma position is measured using saddle-loops and Rogowski coil and is controlled by electromagnetic forces generated by passing currents through control coils placed around the plasma. A desired control objective is maintaining the plasma in the center of vacuum vessel and to stabilize the plasma in the presence of disturbances in a time domain of the order of few milliseconds. In order to achieve maximum performance it is essential to optimize the control system. In this paper plasma position measurement and the details of implementing high-speed PID controllers based on a TMS320c25 digital signal processor along with the system optimization are presented.     

Conformally coupled scalars, instantons, and vacuum instability in 4D anti-de Sitter space

We show that a scalar field conformally coupled to AdS gravity in four dimensions with a quartic self-interaction can be embedded into M theory. The holographic effective potential is exactly calculated, allowing us to study nonperturbatively the stability of AdS4 in the presence of the conformally coupled scalar. It is shown that there exists a one-parameter family of conformal scalar boundary conditions for which the boundary theory has an unstable vacuum. In this case, the bulk theory has instanton solutions that mediate the decay of the AdS4 space. These results match nicely with the vacuum structure and the existence of instantons in an effective three-dimensional boundary model.     

Axial feedback stabilization of flute modes for mirror machines

A novel scheme of feedback stabilization of the m=1 flute mode for axisymmetric mirror machines is proposed that has potential for reactor extrapolation. A three-region plasma model is analyzed, consisting of a hot core surrounded by a warm transition annulus, which in turn is surrounded by a warm halo annulus that is in contact with segmented annular feedback plates at the two end walls. For plasma parameters characteristic of the TMX-U and MFTF-B devices at the Lawrence Livermore National Laboratory and the MMX device at the University of California, Berkeley, the required feedback power is calculated. The results show that stability can be achieved in the MMX and TMX-U devices with a modest feedback gain and power. The power requirement for the near-reactor conditions of MFTF-B is more severe, but can be reduced by a modified choice of plasma parameters     

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等离子体破裂时随着等离子体电流的迅速衰减会在托卡马克装置真空室上产生很大的感应电流并导致电磁力。将EAST 装置真空室双层结构简化为若干环形线圈,采用互感矩阵法对破裂后真空室上感应电流及其导致的电磁力进行了模拟,用Fortran软件分析了真空室上感应电流、磁场、电磁力的变化规律。所得结果为未来托卡马克装置的工程设计改造提供理论依据。     

On the influence of dissipative effects on instabilities of differentially-rotating plasmas

The stability of differentially-rotating cylindrical plasmas in the axial homogeneous magnetic field is studied in the framework of one-fluid dissipative magnetohydrodynamics. The dispersion relation of small-scale axisymmetric perturbations, taking into account the effects of the plasma thermal stratification, its resistivity and its viscosity, is derived. In the limiting cases of negligible resistivity and of negligible viscosity, the criteria of plasma stability are obtained. It is shown that in the case of small viscosity, the azimuthal flow of resistive plasma in the axial magnetic field is unstable due to the buoyancy effect if both the plasma pressure and its entropy either increase or decrease in the radial direction.     

Comparative measurements of plasma position using coils,hall probes,and bolometers on CASTOR tokamak

Plasma position on CASTOR tokamak is measured by several systems based on different experimental methods. Vertical and horizontal plasma displacements are deduced from data of 4 Mirnov coils spaced poloidaly by 45°. Output of the Mirnov coils is routinely used as an input for automatic feed-back control of plasma position on CASTOR. Independently, we used an array of 16 Hall sensors, which measure the required magnetic field directly. Additional information on plasma position is obtained from two arrays of bolometers that measure horizontal and vertical profile of plasma radiation. Principle design of the all used diagnostics is given. Comparison of horizontal and vertical displacements deduced using various experimental methods is presented.     

The Effective Mode Approximation for Analyzing Position Instability of a Tokamak Plasma

The effect of induced currents in the equilibrium field (EF) coils on ameliorating the instability of a small position perturbation of a rigid tokamak plasma is analyzed. A strong analogy between the position instability of the plasma and supercriticality of a fission reactor core is recognized. The position of the plasma corresponds to the neutron population, and the retardation of the displacement by the induced eddy currents to the suppression of population growth by delayed neutrons. The matrix equation of the dispersion relation for the position instability is diagonalized and factored into a form identical to the in-hour equation of fission reactor kinetics. An Effecitve Mode Approximation (EMA) similar to the one group of delayed neutron approximation has been introduced to greatly simplify the analysis of the position instability and feedback control. With this approximation the dispersion relation is reduced to a linear or cubic algebraic equation depending on the effectiveness of retardation by the eddy currents. The time constant of the unstable mode can be expressed in terms of the plasma parameters and the effective resistance and inductance of the current carriers, which can be conveniently computed. The vertical instability of a typical noncircular tokamak plasma is analyzed numerically as well as analytically by the EMA method. The results agree well within a negligible discrepancy.     

Resonant helical divertor

A concept for a helical divertor is proposed, which utilizes a resonance effect, and reduces the required divertor currents to a small fraction (typically 10^-2) of the plasma current. This divertor should have a larger screening efficiency than the poloidal field divertor, and could operate with divertor coils outside the vacuum vessel or the blanket.     

带铁芯托卡马克装置的等离子体平衡数值解法

本文提出一种计算铁芯变压器托卡马克装置中等离子体平衡的数值方法。将铁芯对等离子体平衡的影响等效地看作外部线圈电流的作用,这样问题就转化为求解空芯变压器装置的等离子体平衡问题。这一方法的另一特点是计算区域减至最小。     

Instability criteria for steady flows of a perfect fluid

An instability criterion based on the positivity of a Lyapunov-type exponent is used to study the stability of the Euler equations governing the motion of an inviscid incompressible fluid. It is proved that any flow with exponential stretching of the fluid particles is unstable. In the case of an arbitrary axisymmetric steady integrable flow, a sufficient condition for instability is exhibited in terms of the curvature and the geodesic torsion of a stream line and the helicity of the flow.     

HT－7托卡马克中等离子体平衡研究

本文解决了二维轴对称近似下带铁芯的托卡马克中等离子体平衡问题，计算了ＨＴ－７托卡马克中的等离子体平衡位形以及极向场系统的非线性电感和垂直场系数。最后应用Ｋｉｒｃｈｈｏｆｆ方程组和平衡垂直场公式得到了一组等离子体、加热场和垂直场线圈的电流波形的自洽曲线。