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.     

Spontaneous magnetic field multipolar structure in toroidal plasmas based on 2D equilibrium

The multipolar magnetic field structure is investigated by the momentum conservation equation with self-consistent 3D sheared flows during transition of plasma properties from local paramagnetic to diamagnetic fields. Numerical results show that the traditional poloidal magnetic field (B_P) is one part of equilibrium magnetic fields. The non-zero-order quantities are originated from the higher-order terms of 2D equilibrium treatment based on a Fourier expansion of ψ (r, θ). The distributions of magnetic field vectors of the order of 1, 2, and 3 terms are presented respectively in two, four, and six polar fields with the local vortex structures (spontaneous magnetic connection). The excitation mechanisms of the magnetic vortices are the coupling effects of the magnetic fluid structure pattern and the toroidal effects. These results can help us understand the physical mechanism of the interaction between the external perturbation fields and control tearing modes, as well as the radial plasma flow and magnetic vortices.     

Design,simulation and construction of the Taban tokamak

This paper describes the design and construction of the Taban tokamak, which is located in Amirkabir University of Technology, Tehran, Iran. The Taban tokamak was designed for plasma investigation. The design, simulation and construction of essential parts of the Taban tokamak such as the toroidal field(TF) system, ohmic heating(OH) system and equilibrium field system and their power supplies are presented. For the Taban tokamak, the toroidal magnetic coil was designed to produce a maximum field of 0.7 T at R?=?0.45 m. The power supply of the TF was a130 kJ, 0–10 kV capacitor bank. Ripples of toroidal magnetic field at the plasma edge and plasma center are 0.2% and 0.014%, respectively. For the OH system with 3 kA current, the stray field in the plasma region is less than 40 G over 80% of the plasma volume. The power supply of the OH system consists of two stages, as follows. The fast bank stage is a 120 μF, 0–5 k V capacitor that produces 2.5 kA in 400 μs and the slow bank stage is 93 mF, 600 V that can produce a maximum of 3 kA. The equilibrium system can produce uniform magnetic field at plasma volume. This system's power supply, like the OH system, consists of two stages, so that the fast bank stage is 500 μF, 800 V and the slow bank stage is 110 mF, 200 V.     

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.     

海关集装箱检测用电子直线加速器聚焦线圈磁场设计与测试

介绍了在电子直线加速器粒子动力学基础上进行聚焦线圈轴向磁场的设计；利用ＬＩＮＥ－ＡＣＣ／ＰＣ程序模拟计算，给出了不同初始发射度情况下满足束流包络要求的各种聚焦磁场数据。对已经加工好的聚焦系统进行了磁场分布测量，并将实际磁场与理论计算进行了比较。上述工作为确定聚焦线圈的设计方案和加速器的出束实验提供了可靠、丰富的数据。     

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。     

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。     

The Influence of Magnetic Permeability on the Configuration of magnetic Field in Helimak Device

The Helimak of USA is a plasma physics experimental device designed and built by CASIPP.Its configuration of magnetic field is of very importance during the operation of this device.In this paper,the influence of magnetic permeability on configuration of magnetic field will be discussed due to the effect of weld metal in the vacuum vessel of Helimak,and some conclusion is useful for some engineering designs of the fusion experimental device.     

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.     

加速器磁场测量的霍尔多探头装置

描述了用于加速器磁场测量的霍尔多探头装置,它包括一个具有三只恒温盒(内有58只霍尔片)的测磁长臂,高精度磁场检定系统以及数据自动获取系统。分别叙述了霍尔片的定位、恒温、校准、数据采集、处理等内容。并提出了多探头装置测量中霍尔片稳定性的重要性。给出了在我们条件下的一些具体数据。本装置已应用在兰州重离子研究装置(HIRFL)的建造过程中,实践证明它能有效地高质量地满足加速器磁场测量的要求。     

Effects of pulsed magnetic field on density reduction of high flow velocity plasma sheath

A three-dimensional model is proposed in this paper to study the effect of the pulsed magnetic field on the density distribution of high flow velocity plasma sheath. Taking the typical parameters of plasma sheath at the height of 71 km as an example, the distribution characteristics and time evolution characteristics of plasma density in the flow field under the action of pulsed magnetic field, as well as the effect of self-electric field on the distribution of plasma density, are studied. The simulation results show that pulsed magnetic field can effectively reduce the density of plasma sheath. Meanwhile, the simulation results of three-dimensional plasma density distribution show that the size of the density reduction area is large enough to meet the communication requirements of the Global Position System(GPS) signal. Besides, the location of density reduction area provides a reference for the appropriate location of antenna. The time evolution of plasma density shows that the effective density reduction time can reach 62% of the pulse duration, and the maximum reduction of plasma density can reach 55%. Based on the simulation results, the mechanism of the interaction between pulsed magnetic field and plasma flow field is physically analyzed. Furthermore, the simulation results indicate that the density distributions of electrons and ions are consistent under the action of plasma self-electric field.However, the quasi neutral assumption of plasma in the flow field is not appropriate, because the self-electric field of plasma will weaken the effect of the pulsed magnetic field on the reduction of electron density, which cannot be ignored. The calculation results could provide useful information for the mitigation of communication blackout in hypersonic vehicles.     

脉冲强磁场发展技术

本文叙述了国内外脉冲磁场的发展状况，并给出了脉冲强磁场的几种产生方法、发展水平和目前在磁场设计中亟待解决的问题，最后对未来强磁场的发展进行了一些展望。     

模拟有源积分器在脉冲磁场测量中的分析和应用

本文介绍了应用于脉冲磁场测量系统中的模拟有源积分器的研制.针对测量系统的需求和精度要求,设计了积分电路,并对实际有源积分电路的设计参数和器件参数做了误差分析,论证了电路的可行性和合理性,并给出了合理电路设计的有关参数和误差控制范围.电路实验和测试表明,脉冲磁场测量模拟有源积分器电路达到了设计要求,可满足磁测系统的需求.     

Numerical simulation of the plasma acceleration process in a magnetically enhanced micro-cathode vacuum arc thruster

A particle-in-cell simulation is conducted to investigate the plasma acceleration process in a micro-cathode vacuum arc thruster. A coaxial electrode structure thruster with an applied magnetic field configuration is used to investigate the effects of the distribution of the magnetic field on the acceleration process and the mechanism of electrons and ions. The modeling results show that due to the small Larmor radius of electrons, they are magnetized and bound by the magnetic field lines to form a narrow electron channel. Heavy ions with a large Larmor radius take a long time to keep up with the electron movement. The presence of a magnetic field strengthens the charge separation phenomenon. The electric field caused by the charge separation is mainly responsible for the ion acceleration downstream of the computation. The impact of variations in the distribution of the magnetic field on the acceleration of the plasma is also investigated in this study, and it is found that the position of the magnetic coil relative to the thruster exit has an important impact on the acceleration of ions. In order to increase the axial velocity of heavy ions, the design should be considered to reduce the confinement of the magnetic field on the electrons in the downstream divergent part of the applied magnetic field.     

径向非均匀场分析磁铁出入射界面机械边界的确定

文章介绍了采用锥形极面且具有园弧形入射磁场边界的径向非均匀场分析磁铁出入射界面机械边界的确定方法。用一系列二维磁场计算来近似边界面附近的三维场计算,求得磁场等效边界与磁铁机械边界之间的关系,据此计算出与要求的场分布对应的机械边界的形状,并用合适的圆形弧边界代替所求得的曲线边界,确定出机械边界的实际参数。对于计算中采用的近似方法可能导致的偏差及其对系统光学性能的影响进行了详细的分析,并选用有效的修正措施保证了系统的光学参数满足设计要求。     

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。     

Experiment on low-frequency electromagnetic waves propagating in shock-tube-generated magnetized cylindrical enveloping plasma

We propose a method of applying a static magnetic field to reduce the attenuation of the magnetic field component(S_H) of low-frequency electromagnetic(LF EM) waves in dense plasma. The principle of this method is to apply a static magnetic field to limit electron movement, thereby increasing the equivalent resistance and thus reducing the induced current and S_H. We consider the static magnetic field acting on the plasma of the entire induced current loop rather than on the local plasma, where the induced current is excited by the magnetic field component of LF EM waves. Analytical expressions of S_H suitable for magnetized cylindrical enveloping plasma are derived by adopting an equivalent circuit approach, by which S_His calculated with respect to various plasma parameter settings. The results show that S_H can be reduced under a static magnetic field and the maximum magnetic field strength that mitigates blackout is less than 0.1 T. Experiments in which LF EM waves propagate in a shock-tubegenerated magnetized cylindrical enveloping plasma are also conducted. S_H measured under the magnetic field(the magnetic field strength B0 acting on the magnetic field probe was about0.06 T) reduces at f=10 MHz and f=30 MHz when n_e≈1.9×10~(13) cm~(-3), which is consistent with theoretical results. The verification of the theory thus suggests that applying a static magnetic field with a weak magnetic field has the potential to improve the transmission capacity of LF EM waves in dense plasma.     

Numerical study of the effect of aft-loaded magnetic field on multiple ionizations in Hall thruster

It is assumed that the shift of a strong magnetic field region with a positive gradient from exit plane to outside, namely the transit from a normal loaded magnetic field to an aft-loaded one, enhances the multiple ionization process in the magnetically shielded Hall thruster. To confirm this conjecture, a comparative study is carried out numerically with a particle-in-cell method. The simulation results prove that compared with the normal loaded magnetic field, the application of aft-loaded magnetic field enhances the multiple ionization process. This study further analyzes the ionization characteristics of the transition from low-charged ions to high-charged ions under two magnetic field conditions and the influence of the magnetic strength of aft-loaded magnetic field on the multiple ionization characteristics. The study described herein is useful for understanding the discharge characteristics of Hall thruster with an aft-loaded magnetic field.     

Modelling effect of magnetic field on material removal in dry electrical discharge machining

One of the reasons for increased material removal rate in magnetic field assisted dry electrical discharge machining(EDM) is confinement of plasma due to Lorentz forces.This paper presents a mathematical model to evaluate the effect of external magnetic field on crater depth and diameter in single-and multiple-discharge EDM process.The model incorporates three main effects of the magnetic field,which include plasma confinement,mean free path reduction and pulsating magnetic field effects.Upon the application of an external magnetic field,Lorentz forces that are developed across the plasma column confine the plasma column.Also,the magnetic field reduces the mean free path of electrons due to an increase in the plasma pressure and cycloidal path taken by the electrons between the electrodes.As the mean free path of electrons reduces,more ionization occurs in plasma column and eventually an increase in the current density at the inter-electrode gap occurs.The model results for crater depth and its diameter in single discharge dry EDM process show an error of 9%-10%over the respective experimental values.     

基于SOPC架构的脉冲磁场数据采集系统

提出了一种嵌入式高速高精度脉冲磁场数据采集系统的设计方案,基于先进SOPC技术,在FPGA中嵌入了32位Nios Ⅱ软核系统,实现脉冲磁场信号的采集、处理、存储、传输等功能.该系统具有设计灵活、数据处理速度快、精度高和扩展性好等优点.