行波磁场提升装置的分析及实验研究

行波磁场提升装置作为ADS颗粒流靶的循环靶系统,实现了钨基合金球靶材的电磁提升。其基本原理是加载三相电的螺线管产生行波磁场,磁场作用于靶材,实现靶材的输运。实验中,通过调节输入三相电的幅值和频率来获得提升靶材的不同电磁力,以达到控制靶材输运速度的目的。本文利用Ansys Maxwell对提升装置的模型进行了数值模拟,分析了输运管道中的磁场分布、合金球的受力以及电流幅值和频率对靶材电磁力的影响等。在数值分析的基础上完成了装置的实验研究,实验结果显示,基于行波原理的提升装置达到了输运一定量钨基合金球靶材的目的。     

Magnetic configuration studies in a Compact Torsatron

An overview is presented of an experimental program of magnetic field line mapping on the research-grade Compact Auburn Torsatron (CAT). The vacuum magnetic flux surfaces of the CAT device have been experimentally mapped in a variety of magnetic configurations. The results are compared with an extensive computer model in order to validate the coil design. In initial field mapping experiments, an up-down asymmetry was identified in the vacuum magnetic surfaces, and was corrected with the use of a radial trim field. Magnetic islands are observed and their size has been reduced, also through the use of auxiliary trim coils. The Compact Auburn Torsatron is equipped with two pairs of large Helmholtz coils producing mutually orthogonal magnetic fields in the horizontal plane, and two pairs of helical saddle coils wound directly on the toroidal vacuum vessel. These trim coils are used to control the size and phase of the t=1/2 magnetic island. Through a systematic variation of trim field components, we demonstrate a reduction of the inherent t=1/2 magnetic island size by a factor of three. The technique is applicable to correcting small error fields in larger helical confinement devices. The measurements of island size are compared with measurements of magnetic field line rotation within the island, and are found to be in good agreement with first-order perturbation theory.     

H 1NF仿星器标准磁场位形分析与高能量离子运动轨道模拟

本文分析了H 1NF仿星器的磁场线圈组成与分布特征,研究了其在标准运行模式下的磁场位形特点,并模拟计算出高能量离子在该标准磁场位形中的典型运动轨道。基于H 1NF仿星器标准磁场位形的磁轴位置和磁面沿环向角的变化规律,以磁轴为旋转轴,按照旋转规律将不同环向角的极向截面旋转后得到一种旋转坐标系下的等效标定极向截面,并将高能量离子的三维运动轨道投影到这种等效标定极向截面上,从而可更加清晰地显示出高能量离子在该磁场位形中的运动轨道特征。结果表明,H 1NF仿星器中的通行粒子和捕获粒子轨道特征均与一般托卡马克中的相应粒子轨道特征相似,但H 1NF仿星器中的通行粒子轨道在等效标定极向截面上绕几圈后才闭合,H 1NF仿星器中捕获粒子的香蕉轨道没有闭合,且轨道逐渐向磁面外侧漂移,最终可能导致粒子损失。     

Initial Vacuum Magnetic Field Mapping in the Compact Toroidal Hybrid

The Compact Toroidal Hybrid (CTH) is a low aspect ratio (R/a_plasma ≥ 3.5, R₀ = 0.75 m, a_vessel = 0.29 m, B ≤ 0.6 T) torsatron with a highly flexible vacuum magnetic field configuration designed for current-driven instability studies. Vacuum magnetic field mapping of the completed configuration is performed using a movable electron gun and phosphor-coated screen. These experiments compare the actual magnetic configuration with the design, verify the range of accessible magnetic configurations, and identify vacuum field errors. The main helical field is produced by a continuously-wound helical coil, and the vacuum rotational transform is varied with a set of toroidal field coils. Four independent poloidal field coil sets provide equilibrium control and shaping, and are also used for ohmic current drive.     

球形环研究概述

球形环是一种先进的磁约束核聚变研究装置 ,它保留了传统托卡马克装置的许多特点 ,比如说封闭磁面系统 ,中等旋转变换磁力线和好的等离子体约束性能等 ,同时又有低环径比 ,低纵向磁场 ,从而具有结构紧凑 ,造价相对低廉等优点 ,是有潜力的磁约束核聚变途径之一。概述了球形环的装置、实验、理论等方面的研究现状和有待探索的问题     

单脉冲磁场精确设定装置的研制

本文介绍了一种用于磁镜装置研究中脉冲磁场精确设定的装置，其重复精度误差小于１／１０００。     

Analysis of Magnetic Field of the DNB Ion Source

A distribution of the magnetic field produced by permanent magnets in the DNB ion source is calculated and analyzed in order to understand the plasma confinement in a cusped magnetic field and optimize plasma discharge. A uniform plasma is obtained in the experiment.     

Redistribution of Gaseous Phase of Liquid Metal Two-Phase Flow in a Strong Magnetic Field

In the previous paper, the authors pointed out the motion of bubble or gaseous phase in the direction to the both side walls due to the pinch effect caused by the induced magnetic field in the liquid metal two-phase flow under the strong magnetic field. In the present paper, to clarify the existence of the pinch effect experimentally, an experimental study was performed.

Firstly the distributions of the void fraction in the cross section perpendicular to the flow were measured at three locations in the flow direction for the various strength of the applied magnetic field. Secondly a magnetic field was superposed on the induced magnetic field by the outer coil to disturb the pinch effect by the cancel of the induced magnetic field with the superposed one, resulting in the evident redistribution of the void-fraction profile obtained above.

From these experiments it is concluded that the pinch effect will play an important role to redistribute the bubble or gaseous phase in the liquid metal two-phase flow under the strong magnetic field and that the effect is more promoted with increasing magnetic interaction number defined as a ratio of the electromagnetic force to the inertia of the fluid.     

Particle-in-Cell Modeling of Field Reversed Configuration Formation by Odd-parity Rotating Magnetic Fields

We describe kinetic electromagnetic particle-in-cell simulation of a field reversed configuration with rotating magnetic fields (RMF). The energy-conserving algorithm calculates RMF penetration, gas breakdown and field reversal for the odd-parity RMF, PFRC device. An advanced simulation technique is being developed that preserves charged particle orbits for large time steps. These techniques are being developed to model future devices.     

Magnetic configuration flexibility of snowflake divertor for HL-2M

HL-2M (Li, 2013 [1]) is a tokamak device that is under construction. Based on the magnetic coils design of HL-2M, four kinds of divertor configurations are calculated by CORSICA code (Pearlstein et al., 2001 [2]) with the same main plasma parameters, which are standard divertor, exact snowflake divertor, snowflake-plus divertor and snowflake-minus divertor configurations. The potential properties of these divertors are analyzed and presented in this paper: low poloidal field area around X-point, connection length from outside mid-plane to the primary X-point, target plate design and magnetic field shear. The results show that the snowflake configurations not only can reduce the heat load at divertor target plates, but also may improve the magneto-hydrodynamic stability by stronger magnetic shear at the edge. A new divertor configuration, named “tripod divertor”, is designed by adjusting the positions of the two X-points according to plasma parameters and magnetic coils current of HL-2M.     

Research on Nanosecond Pulse Corona Discharge with Cross Magnetic Field Applied

An application of magnetic field to the nanosecond pulse corona discharge is investigated. A cylinder reactor with different corona electrodes is set up for experimental study. A magnetic field with its direction perpendicular to the corona discharge is applied. Different discharge images are taken under single nanosecond pulse with a high sensitive UV-visible light imagine recorder. Experimental results show that with a cross magnetic field the nanosecond corona discharge both generates paths and develops homogeneously in space more than that without the magnetic field. The results may lead to a possibility to apply a cross magnetic field on nanosecond pulse corona discharge for getting higher desulfurization efficiency.     

Experimental Study of the Effect of Applied Magnetic Field on Plasma Properties of Unbalanced Magnetron Sputtering

An experimental study of the effect of applied magnetic field on the properties of the plasma and electrostatic oscillations in an unbalanced magnetron sputtering discharge was carried out. The apparatus consists of a magnetron sputtering target, using the conventional magnetic field configuration, and a coaxial coil around the target for an applied axial magnetic field. The dependencies of plasma parameters on the coil current were studied by two Langmuir probes. The resonance properties of electrostatic oscillations were observed. The results indicate that the applied magnetic field affects the plasma properties for the coil current in a range of 0 to 8 A. The frequency bandwidth of the electrostatic oscillations in the unbalanced magnetron sputtering plasma is in a range of 0 to 300 kHz. From the spectrum analysis, the eigenfrequency near the target is in a range of 20 to 50 kHz under typical experimental conditions where all the magnetic field, pressure, and power etc are able to have full impact on the spectrum characteristics. The calculated value of the electron temperature as per an ion acoustic standing wave pattern inside the magnetic trap is in good agreement with the experimental result.     

An Experimental Platform for the Study on Magnetic Reconnection in Laboratory Plasmas

In order to investigate electron dynamics near the electron diffusion region in magnetic reconnection process, an upgrade in the Linear Magnetized Plasma (LMP) device is accomplished at the University of Science and Technology of China. Radio frequency (RF) helicon discharge is used to generate a quasi-stationary plasma, and a time-dependent magnetic field is applied to the plasma, which exhibits an X-type neutral point in vacuum. A two-dimensional sophisticated mobile platform is built up, providing a high spatial resolution, below 0.5mm, for the diagnostics.     

Experimental observation of the transport induced by ion Bernstein waves near the separatrix of magnetic nulls

The waves in a magnetic null could play important roles during 3D magnetic reconnection. Some preliminary clues in this paper show that the ion Bernstein wave (IBW) may be closely related to transport process in magnetic null region. The magnetic null configuration experiment reported here is set up in a linear helicon plasma device, Peking University plasma test device (PPT). The wave modes with frequencies between the first and third harmonics of local ion cyclotron frequency (${\omega }_{{\rm{ci}}}$) are observed in the separatrix of magnetic null, which are identified as the IBW based on the dispersion relation. Further analysis shows that IBW could drive substantial particle flux across the magnetic separatrix. The theoretical radial particle flux driven by IBW and the measured parallel flow in PPT device are almost on the same order, which shows that IBW may play an important role during 3D reconnection process.     

基于台阶垫补的磁场优化算法研究

在回旋加速器磁铁设计过程中,磁场优化是非常重要的一个环节。由于加速器磁铁的磁场响应随着磁极台阶高度变化呈现非线性的特点,使得在优化复杂的磁场时,计算过程复杂、时间成本高且需要手动迭代。以1台圆形轴对称磁铁垫补为例,发展了磁场优化算法。利用三维电磁场仿真软件CST和数据分析软件MATLAB,研究了单个台阶垫补块对中心平面上不同半径处磁场幅值的影响,实现了一种自动优化磁场的算法,并以磁场降落指数为0.2的磁场为优化模拟实例,最终求得了对应的磁极台阶高度,证明了本算法的可行性和便捷性。     

The Drift of Dust Grains Induced by Transient Magnetic Field

Our experiment shows that the dust grains ,suspended on the edge of the sheath of a radio-frequency discharge,undergo a contraction when switching a vertical magnetic field on ,and an expansion when switching the magnetic field off .We call this kind of magnetic field“transient magnetic field”.A primary analysis is proposed for the phenomenon.     

Simulation study on electron heating characteristics in magnetic enhancement capacitively coupled plasmas with a longitudinal magnetic field

The electron heating characteristics of magnetic enhancement capacitively coupled argon plasmas in presence of both longitudinal and transverse uniform magnetic field have been explored through both theoretical and numerical calculations. It is found that the longitudinal magnetic field can affect the heating by changing the level of the pressure heating along the longitudinal direction and that of the Ohmic heating along the direction which is perpendicular to both driving electric field and the applied transverse magnetic field, and a continuously increased longitudinal magnetic field can induce pressure heating to become dominant. Moreover, the electron temperature as well as proportion of some low energy electrons will increase if a small longitudinal magnetic field is introduced, which is attributed to the increased average electron energy. We believe that the research will provide guidance for optimizing the magnetic field configuration of some discharge systems having both transverse and longitudinal magnetic field.     

Magnetic configuration effects on the edge heat flux in the limiter plasma on W7-X measured using the infrared camera and the combined probe

Controlling the heat and particle fluxes in the plasma edge and on the plasma facing components is important for the safe and effective operation of every magnetically confined fusion device. This was attempted on Wendelstein 7-X in the first operational campaign, with the modification of the magnetic configuration by use of the trim coils and tuning the field coil currents,commonly named iota scan. Ideally, the heat loads on the five limiters are equal. However, they differ between each limiter and are non-uniform, due to the (relatively small) error fields caused by the misalignment of components. It is therefore necessary to study the influence of the configuration changes on the transport of heat and particles in the plasma edge caused by the application of error fields and the change of the magnetic configuration. In this paper the upstream measurements conducted with the combined probe are compared to the downstream measurements with the DIAS infrared camera on the limiter.     

Magnetic field topology modeling under resonant magnetic perturbations on EAST

In order to understand the mechanism by which the resonant magnetic perturbation (RMP) mitigates or suppresses the edge-localized mode (ELM), the topological study of the edge magnetic field in ELM mitigation or suppression phase is a critical issue. To model the three-dimensional magnetic field topology superposed RMP on Experimental Advanced Superconducting Tokamak, a numerical model using the field line tracing method for both vacuum and ideal plasma response approximations is proposed. Using the numerical model, the topological change and the penetration depth of the stochastic field lines in the edge magnetic field are studied in an RMP experiment. Comparing profiles of minimum ρ on edge stochastic field lines and the particle flux pattern, the ideal plasma response changes the field line penetration depth while remaining similar profile relative to vacuum approximation. To mitigate and suppress ELM strongly, the deep penetration of RMP fields and topological changes of the edge magnetic field is a key from our modeling.     

Vacuum Poloidal Magnetic Field of Tokamak in Alternating-Current Operation

Vacuum poloidal magnetic field of tokamak in alternating-current (AC) operation is investigated. It is found that the vacuum magnetic field in AC operation is qualitatively different from that in direct-current (DC) operation. In the DC case, the vacuum magnetic field varies along the poloidal direction with one period, while in the AC case, the vacuum magnetic field varies along the poloidal direction with two periods. This implies that two sets of vertical field coil may be needed for the AC operation.