A Modular Stellarator Divertor

Modular stellarators, like continuous-helix steliarators, are characterized by a magnetic limiter and built-in divertor. We have found this divertor to be modular in nature. The magnetic structure of the divertor has been studied numerically for several different configurations. The divertor consists of a number of small localized flux bundles which resemble bundle divertors distributed over the torus. The impact of the divertor system on experimental design and a conceptual reactor study has been investigated in some detail.     

Status of Stellarator Experiments?1981

During the last years growing interest in stellarators as toroidal magnetic confinement devices becomes evident. In spite of many restrictions, e.g., small minor radius a ~0.1 m, plasma parameters comparable to those in tokamaks have been achieved. The deleterious effect of the plasma current on stability, equilibrium, and transport could be clarified. The progress of heating by the use of neutral injection and RF, allows to substitute ohmic heating. In the currentless phase significant improvement of the confinement at reasonable parameters has been observed. The substantial reduction of low-frequency and MHD fluctuations seems related to a decreased electron heat conduction.     

Quasioptical Transmission Lines for ECRH at TJ-II Stellarator

Two mirror lines have been used to transmit the microwave power from the powerful microwave generators to the TJ-II plasmas. Both lines have been tested at nominal power level and they are in operation now. This paper deals with the final design of the transmission lines and their testing. Before starting operation at high power level, measurements of the wave beam parameters at low power level were performed. Two horn antennas were designed to simulate the gyrotron output. The results are presented in this paper. A computer code based on Huygens diffraction theory was developed to simulate the propagation of the beam along the mirror lines. A comparison of the theoretical and the experimental results is also shown here.     

ESTELL: A Quasi‐Toroidally Symmetric Stellarator

This work presents the physics design for a simple quasi‐axially symmetric stellarator. A plasma configuration described by a modest number of Fourier coefficients was found to establish this symmetry with good accuracy. The low rotational transform results in a relatively simple coil set exhibiting low curvatures and comfortable clearance between adjacent coils. As another consequence, the maximum achievable plasma pressure will be limited to about 0.5%. An experiment along the lines proposed would allow an exploration of the confinement properties of a quasi‐axially symmetric configuration. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Visible Intensified Cameras for Plasma Imaging in the TJ‐II Stellarator

Visible cameras are widely used in fusion experiments for diagnosis and for machine safety issues. They are generally used to monitor the plasma emission, but are also sensible to surface Blackbody radiation and Bremsstrahlung. Fast or high speed cameras capable of operating in the 10⁵ frames per second speed range are today commercially available and offer the opportunity to plasma fusion researchers of two‐dimensional (2D) imaging of fast phenomena such as turbulence, ELMs, disruptions, dust, etc. The tracking of these fast phenomena requires short exposure times down to the μ s range and the light intensity can be often near the signal to noise ratio limit especially in low plasma emission regions such as the far SOL Additionally, when using interference filters to monitor, e.g. impurity line emission, the photon flux is strongly reduced and the emission cannot be imaged at high speed. Therefore, the use of image intensifiers that amplify the light intensity onto the camera sensor can be of great help. The present work describes the use of intensifiers in the visible fast cameras of TJ‐II stellarator. We have achieved spectroscopic plasma imaging of filtered impurity atomic line emission at short exposure times down to the 10 μ s range depending on atomic line and concentration. Additionally, plasma movies at velocities of 2x10⁵ frames per second near the camera operation limit can be recorded with exposure times well below 1 μ s with sufficient signal to noise ratio. Although an increasing degradation of the image quality appears when raising the light amplification, an effective gain of up to two orders of magnitude of the light intensity is feasible for many applications (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Edge Turbulence During Limiter Biasing Experiments in the TJ-II Stellarator

The influence of limiter biasing on plasma confinement, turbulence and plasma flows has been investigated in the TJ-II stellarator. Experimental results show that it is possible to modify global particle confinement and edge plasma parameters with both positive and negative biasing. Significant and minor modifications in the structure of plasma fluctuations have been observed during the transition to improved confinement regimes induced by limiter biasing. These results show evidence of electric field induced improved confinement via multiple mechanisms. The investigation of the relaxation of plasma potential and electric fields shows evidence of two different characteristic decay times.     

基于优度评价方法的面向信号软件平台中的仪器更换研究

针对现在维护ATS时遇到的对仪器更换方案很难选择的问题,首先讨论在维护ATS时,更换ATS中仪器的必要性,并介绍面向信号ATS软件平台给测试带来的便利,然后在面向信号ATS软件平台的基础上使用可拓学中物元模型较为完善的对仪器进行形式化的描述,并通过蕴含分析和发散分析来生成仪器的更换方案,最后通过一个简单的例子介绍使用优度评价方法来定量描述仪器更换方案的优劣以选择较优的更换方案。     

The Influence of Stochastic Layers of Magnetic Field Lines on Transport Barrier Formation in a Stellarator System

The results of local measurements of RF discharge plasma parameters in the process of internal transport barriers (ITB) formation in the vicinity of rational magnetic surfaces in the Uragan-3M torsatron are presented. The following phenomena were observed in the process of ITB formation: widening of the radial density distribution, formation of plateaus on radial density and electron temperature distributions, formation of regions with high shear of poloidal plasma rotation velocity and radial electric field in the vicinity of stochastic layers of magnetic field lines, decrease of density fluctuations and their radial correlation length, decorrelation of density fluctuations, and increase of the bootstrap current.After the ITB formation, the transition to the improved plasma confinement regime takes place. The transition moves to the beginning of the discharge with the increase of heating power. The possible mechanism of ITB formation near rational surfaces is discussed.     

Observation of Filamentary Structures on the Boundary Region of the LHD Stellarator

Large Helical Device (LHD) high β regime discharges are observed with a fast camera, with 〈β 〉 values up to almost 5%. High frequency sequences (20 µs between shots) of the density fluctuations in the edge region are obtained. Macroscopic coherent scructures, in the shape of “comet”‐like filaments can be seen in these sequences, propagating from the external ergodic region to the wall. These structures are analyzed and their radial and parallel transport is discussed. Strong relation between the generation of low frequency particle ejections and m/n= 2/3 edge mode is found. In the strike point region, “reflected” structures are observed as a response to ejected filaments. These are discussed in terms of plasma wall interaction phenomena (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

UWTOR-M?a Conceptual Design Study of a Modular Stellarator Power Reactor

A preliminary design of a 5500 MWth modular stellarator power reactor, UWTOR-M, is presented. Discrete twisted coils are used in an Q = 3 configuration with maintainability as a prime consideration. The natural steliarator divertor is used for impurity control in conjunction with innovative high performance divertor targets. A unique blanket design is proposed which minimizes the overall tritium inventory in the reactor. Finally, a scheme for maintaining the first wall/blanket and other reactor components is discussed.     

Identification of Zonal Flows and Their Spatial Distribution in the TJ-II Stellarator Plasmas

JETP Letters - The magnetic and electronic properties of quasi-one-dimensional iron chalcogenide compound KFeS2 have been calculated within two DFT + U approaches based on the simplified LSDA + U...     

A Summary of Containment Experiments on the PROTO-CLEO Stellarator, 1968-1974

This report collects together results on the containment of plasma injected into the PROTO-CLEO stellarator, some of which have been previously presented as conference papers. The importance of fluctuations on plasma containment is also discussed and an attempt made to arrive at momentum balance for the ions and electrons. It is concluded that although plasma can be contained for periods as long as expected on the basis of loss solely by collisions, it cannot be conclusively demonstrated that this is the sole mechanism of plasma loss, since evidence for the existence of the diffusion driven current cannot be found.     

A Spectrally Resolved Motional Stark Effect Diagnostic for the TJ‐II Stellarator

A spectrally resolved motional stark effect (MSE) diagnostic has been implemented for the TJ‐II stellarator to quantify the magnitude and pitch of components of the magnetic field created in this magnetic confinement device. The system includes a compact diagnostic neutral beam injector (DNBI) that provides a short pulse of accelerated neutral hydrogen atoms with an e^–1 beam radius of 2.1 cm to stimulate the Doppler‐displaced Balmer Hαs emissions, which are the basis for this diagnostic. Measurement of the wavelength separation of the Stark splitting of the Hα spectrum, as well as of the relative line intensities of its components, allow the local magnitude and direction of the internal magnetic field components to be measured at 10 positions across the plasma. The use of a DNBI extends such measurements to the electron cyclotron resonance (ECR) heated phases of plasmas while also overcoming the need for the complicated inversion techniques that are required when such measurements are performed with a heating neutral beam injector (NBI). Moreover, the use of the shot‐to‐shot technique with reproducible discharges further simplifies fits to the MSE spectra as nearby impurity spectral emission lines can be eliminated or significantly reduced. After outlining the principles of this technique and the diagnostic set‐up, magnetic field measurements made during ECR or NBI heating phases are reported for a range of magnetic configurations and are compared with vacuum magnetic field estimates in order to evaluate the capabilities and limitations of this diagnostic for the TJ‐II. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An Abundance of K3 Fibrations from Polyhedra with Interchangeable Parts

Even a cursory inspection of the Hodge plot associated with Calabi-Yau threefolds that are hypersurfaces in toric varieties reveals striking structures. These patterns correspond to webs of elliptic-K3 fibrations whose mirror images are also elliptic-K3 fibrations. Such manifolds arise from reflexive polytopes that can be cut into two parts along slices corresponding to the K3 fibers. Any two half-polytopes over a given slice can be combined into a reflexive polytope. This fact, together with a remarkable relation on the additivity of Hodge numbers, explains much of the structure of the observed patterns.     

A Helical Launching Structure for Alfvén Wave Heating in the Proto-Cleo Stellarator

A helical wave launching structure is analyzed to determine the spectrum of Alfvén waves that it can excite. Using an ideal MHD plasma model, the effectiveness of this helical coil for producing Alfvén wave heating in the Proto-Cleo stellarator is investigated. It is found that significant energy absorption should occur. The amount of absorption and the frequency range over which it is greatest are dependent on the shape of the radial profiles of the confining magnetic field and the plasma density.     

CFQS装置准环对称测试用磁体电源系统设计

CFQS装置是中国西南交通大学(SWJTU)和日本国家核融合科学研究所(NIFS)联合设计制造的中国首台准环对称仿星器,为满足装置0.1 T稳态运行的实验要求,需要为其磁体线圈设计相应的电源系统。本设计方案考虑工程实际估算线路阻抗,考虑工程裕度、电源以负载参数的1.2倍进行计算,并建立电源系统的Simulink仿真模型,分析负载电流纹波大小及网侧谐波含量。根据仿真结果优化设计方案,通过在直流侧增加无源滤波器,减小输出电流纹波,分析直流侧电压代数形式,计算滤波器参数,并仿真调节得到更加符合实际需求的滤波器参数,满足装置准环对称位形的分布磁场精度对磁体线圈电流纹波的要求。