Plasma shape optimization for EAST tokamak using orthogonal method

It is necessary to reduce the currents of poloidal field(PF) coils as small as possible, during the static equilibrium design procedure of Experimental Advanced Superconductive Tokamak(EAST). The quasi-snowflake(QSF) divertor configuration is studied in this paper. Starting from a standard QSF plasma equilibrium, a new QSF equilibrium with 300 kA total plasma current is designed. In order to reduce the currents of PF6 and PF14, the influence of plasma shape on PF coil current distribution is analyzed. A fixed boundary equilibrium solver based on a non-rigid plasma model is used to calculate the flux distribution and PF coil current distribution. Then the plasma shape parameters are studied by the orthogonal method. According to the result, the plasma shape is redefined, and the calculated equilibrium shows that the currents of PF6 and PF14 are reduced by 3.592 kA and 2.773 kA, respectively.

Modeling the keyhole shape and dimension in plasma arc welding

It is of great significance to model the keyhole shape and dimensions to optimize the plasma arc welding process parameters. In this study, through employing a combined volumetric heat source mode, the weld pool in keyhole plasma arc welding is determined firstly, and then the dynamic force-balance condition on the interface between the plasma jet and the molten metal is dealt with in describing the keyhole formation inside the weld pool. The effects of welding current on the shape and size of keyhole are numerically analyzed. The sharp transformation from a partial keyhole to a full-penetration keyhole is quantitatively demonstrated.

Formation Mechanism of the Ring-shaped Structure of Plasma Bullet

The formation of plasma bullets’ring-shaped structure in atmospheric pressure helium is analyzed by using a coupled fluid model.The model consists of a two-dimension neutral gas flow module and a one-dimension plasma dynamics module.The obtained radial distributions of the electron’s number density and the nitrogen’s metastable number density have different structures under different types of reactions or air contents in the model.It shows that total electron impact ionization plays an important role in sustaining the discharge,and together with Penning process,they lead to the shifted-off structure of electron number density.Meanwhile,the ring structure of plasma bullets forms mainly due to the excitation reaction of nitrogen molecule on air contents.

Effects of Storage Duration and Temperature of Human Plasma and Serum on Red Blood Cell Aggregation and Shape

Platelet-free plasma of human blood (sodium citrate and EDTA as an anticoagulant) and serum were stored at 4°C, room temperature (25°C) and at 37°C for 24 hours. RBC aggregation decreased after incubation of plasma and serum at 37°C for 4 hours. The RBC shape was changed at the same time: discocytes transformed to echinocytes. Storage of plasma and serum at 4°C and room temperature did not lead to significant alterations of RBC aggregation. The RBC shape did not change in influence of such plasma and serum. The most considerable decrease of RBC aggregation and change of their shapes were observed in the plasma and serum incubated at 37°C for 24 hours. Dilution of incubated plasma by fresh plasma led to consistent restoration of erythrocyte shape and their aggregation.

基于锥形等离子体通道的百拍瓦激光脉冲整形及重离子加速

利用粒子模拟程序研究了百拍瓦极端光场条件下,锥形等离子体通道对激光脉冲的整形和重离子加速的影响.研究发现,由于非线性干涉和聚焦效应,锥形等离子体通道能够整形激光脉冲时空波形并增强激光强度.对于强度为5.46×10^(22)W/cm^(2)、束腰半径为10μm的线偏振激光入射夹角θ=10°的锥形等离子体通道,可获得紧聚焦(束腰半径<1μm)、超高强度(强度提高6倍)的整形激光.利用该激光加速通道末端的超薄平靶发现,辐射反作用力能够有效地抑制由于电子加热和激光强度横向不均匀引起的超薄平靶横向膨胀,延长超薄平靶透明时间,使得金离子得到充分加速,最终可获得截止能量高达约240 GeV的金离子.研究结果有望为未来百PW激光重离子加速实验方案设计及其在核-核碰撞中的应用研究提供理论参考.

基于Python的托卡马克等离子体位形编辑器设计与实现

等离子体位形控制是等离子体实验控制的重要组成部分,设计满足放电要求的等离子体平衡位形是等离子体控制系统的重要功能之一。根据位形计算原理、中国聚变工程实验堆等离子体控制系统用户界面集成原理及用户界面需求,采用开源的Python语言及PyQt库,设计开发位形编辑器,用于等离子体期望位形设计和优化;并提供期望位形输入数据,供其集成使用。对主要模块进行复用,开发可独立运行的位形编辑器,能够灵活适用于不同的托卡马克装置。测试结果显示,该编辑器能满足单机运行的需求,同时消除了必须登录等离子体控制系统才可进行位形设计工作的弊端。

Plasma-MIG复合电弧焊接特性分析

采用Plasma-MIG复合电弧对Q235低碳钢进行堆焊试验,对焊接过程中复合电弧形态、电弧空间分布、焊缝成形及细晶原理进行了分析.结果表明,Plasma-MIG复合电弧焊接过程中,外层等离子电弧单独存在,内层MIG电弧在焊丝端部与外层等离子弧耦合.复合电弧空间温度分布均匀,高温停留时间短,冷却速度快.Plasma-MIG复合电弧在大的等离子电流下,促进填充金属润湿铺展,焊缝熔宽大,成形美观.相同热输入量条件下,等离子电流增大能够促进晶粒自发形核,原奥氏体晶粒及焊缝组织得到细化.

D36海洋平台用钢Plasma-MIG复合电弧焊接工艺研究

D36海洋平台用钢是造船和海洋平台行业不可或缺的材料,本研究采用Plasma-MIG复合电弧焊接实现了厚25 mm的D36钢对接实验。实验表明:采用优化的12道规划路径的Plasma-MIG多层多道焊焊接工艺参数可以满足焊缝宏观形貌要求,焊缝成形美观,无气孔、夹杂、未熔合等缺陷。与传统MIG焊D36钢接头抗拉强度相比,Plasma-MIG复合焊工艺能够提高D36钢的焊接接头强度。Plasma-MIG复合电弧焊接厚25 mm的D36钢焊缝底部的冲击功为62.26 J,中部为103.27 J,顶部为124.68 J,均远大于海洋工程平台建造焊接规范标准的34 J。因此,焊缝具有较好的低温冲击韧性。

高斯与平顶光束纳秒脉冲激光物质蒸发烧蚀动力学仿真研究

基于建立的纳秒脉冲激光与金属铝相互作用的二维轴对称模型,仿真研究了光束整形对纳秒脉冲激光烧蚀金属铝过程中蒸发烧蚀动力学的影响.结果表明:等离子体屏蔽对靶材的烧蚀特性具有显著影响,屏蔽效应主要体现在脉冲的中后期.对于3种激光轮廓,高斯光束的屏蔽效果最强,随着整形后的平顶光束直径的增大,屏蔽效果逐渐减弱.平顶光束与高斯光束作用下,靶材温度的二维空间分布较为不同.高斯光束作用时,靶材中心最先升温,随后温度沿径向和轴向扩散.由于平顶光束的能量分布更加均匀,因此一定径向范围内的靶材同时升温.光束整形对靶材的蒸发烧蚀动力学影响较大.对于高斯光束,靶材中心先烧蚀,随后产生径向烧蚀.由于整形后平顶光束的能量密度降低,因此靶面蒸发时间较高斯光束延后,并且一定径向范围内的靶材同时发生蒸发烧蚀.3种激光轮廓下,靶材的蒸发烧蚀形貌与光束的强度分布类似,其中高斯光束的烧蚀坑呈中间深两边浅的特点,平顶光束的烧蚀坑较为平坦.

发酵豆粕替代鱼粉对黑斑蛙生长性能、体形指数及血浆生化指标的影响

文章旨在研究发酵豆粕替代鱼粉对黑斑蛙生长性能、体形指数及血浆生化指标的影响。试验将800只同批孵化、健康、初重[(2.7±0.1)g]一致的黑斑蛙随机分到20个养殖试验池中,每5个试验池为一组,试验组分别使用0%、10%、20%、40%的发酵豆粕替代基础日粮中的鱼粉,试验为期60 d。结果表明,使用20%和40%的发酵豆粕替代基础日粮中的鱼粉显著降低黑斑蛙6.80%和7.49%的末体重(P<0.05);黑斑蛙的增重率分别显著降低7.84%和7.44%(P<0.05);黑斑蛙的特定生长率分别显著降低3.05%和2.89%(P<0.05);此外,发酵豆粕对黑斑蛙成活率、摄食率和饲料系数均无显著影响(P>0.05)。使用20%和40%的发酵豆粕替代基础日粮中的鱼粉可显著降低黑斑蛙的肥满度和肝体比(P<0.05);使用20%和40%的发酵豆粕替代基础日粮中的鱼粉可显著降低黑斑蛙的胴体比(P<0.05);此外,日粮添加发酵豆粕对黑斑蛙后腿指数和器官指数均无显著影响(P>0.05)。使用20%和40%的发酵豆粕替代基础日粮中的鱼粉可显著降低黑斑蛙血浆TG和HDL含量(P<0.05),显著提高黑斑蛙血浆TC含量(P<0.05);此外,使用发酵豆粕替代基础日粮中的鱼粉对黑斑蛙血浆LDL含量、AST和ALT活性均无显著影响(P>0.05)。结论:使用发酵豆粕替代鱼粉(20%和40%)对黑斑蛙生长性能有显著负面影响,在本试验条件下最适替代量为10%。

柠条收割机圆盘锯式刀片设计与试验

柠条圆盘锯式刀片是收割机的主要零部件之一。在收割运动过程中刀片受力不均匀,且往复循环切割动作导致其易损耗。调研柠条刀片的使用性能及材料特点,研究以特种钢作为刀片基体,在刀刃部表面利用等离子弧熔覆技术进行高合金粉末涂覆,通过优化齿形和热处理工艺参数,获得较优异的耐磨性和强度。经过摩擦磨损试验和作业主体实地收割试验可知,该柠条刀片平茬效果好,使用寿命比同类产品提高了1~2倍。

Physical Engineering Test and First Divertor Plasma Configuration in EAST

Physical engineering capability on the superconducting magnetic system of EAST was tested and first divertor plasma configuration in EAST was obtained. The extrapolation of the safety limit has verified the reliability of the system for long pulse operation. A stably controlled diverted plasmas configuration with an elongation n in excess of 1.8 and plasma current of up to 500 kA, by using the （copper） internal coils to control the vertical displacement instability was obtained by an optimized plasma control algorithm. Highly shaped plasma at various configurations, which almost covers all designed configurations for EAST, was generated stably. A number of operational issues, such as plasma initiation, ramp up and configuration control with constraints of superconducting coils, were successfully investigated. All of the results obtained proved both the capability of the superconducting poloidal magnets for operation under steady-state condition and effectiveness of the plasma control algorithm for EAST.

On the Characteristics of Coaxial-Type Microwave Excited Linear Plasma:a Simple Numerical Analysis

To unveil the characteristics and available propagation mechanism of coaxial-type microwave excited line-shape plasma, the effects of parameters including microwave power, working pressure, dielectric constant, and external magnetic field on the plasma distribution were numerically investigated by solving a coupled system of Maxwell＇s equations and continuity equations. Numerical results indicate that high microwave power, relatively high working pressure, low dielectric constant, and shaped magnetic field profiles will help produce a high-density and uniform plasma source. Exciting both ends by microwave contributed to the high-density and uni- form plasma source as well. Possible mechanisms were analyzed by using the polarization model of low temperature plasma. The generation and propagation processes of the line-shape plasma mainly depend on the interaction of three aspects, i.e. the transmitted part, penetration part and absorptive part of the electromagnetic field. The numerical results were qualitatively consistent with available experimental results from literature. More elaborate descriptions of the three aspects and corresponding interactions among them need to be investigated further to improve the properties of the line-shape plasma.

Operation with 1 MA Plasma Current in EAST

Discharge with a plasma current of 1 MA at a line-averaged density of 1.8× 10^19 m^-3 was realized in EAST, a fully superconducting tokamak. The key issues to achieve the discharge with 1 MA plasma current include both early shaping and LHCD assistance during start-up phase to extend the voltage margin of poloidal field （PF） coils for easier plasma control, an optimization of the control methodology for PF coils to avoid over-current fault and a very good wall condition. A better wall condition was achieved mainly by extensive Lithium coating. Both stationary H- mode and diverted plasma discharge of 100 s were also obtained.

Analytical Theory of the Geodesic Acoustic Mode in the Small and Large Orbit Drift Width Limits and its Application in a Study of Plasma Shaping Effect

Analytical theories of the geodesic acoustic mode （GAM） are reviewed in the small- and large-orbit drift width limits, respectively. Different physics pictures in these two limits are displayed. As an example, these two analytical methods are employed to investigate the plasma shaping effect on the frequency and collisionless damping rate of the GAM.

Determining the keyhole geometry based on double-elliptic distribution of plasma arc pressure

The plasma arc pressure plays an important role in determining the keyhole formation and size. So it is of great significance to choose adaptive distribution mode of the plasma arc pressure for determining keyhole shape and size. In this study, through employing a double-elliptic distribution mode of plasma arc pressure, three-dimensional keyhole was numerically simulated. The unsymmetric feature of the keyhole inside the weld pool was described. The development of keyhole was demonstrated under different levels of welding current. The critical current required to form an open keyhole was obtained for the study cases .

Effects of Finite Aspect Ratio and Noncircular Plasma Flux Surface on Electron Temperature Gradient Driven Modes

A gyrokinetic model with integral eigenmode equations is developed based on the local equilibrium of shaped tokamak plasmas. Effects of main geometric parameters （finite aspect ratio, elongation, triangularity, and Shafranov shift gradient） on the electrostatic electron temper- ature gradient （ETG） driven modes are investigated numerically. It is found that the finite aspect ratio has a general stabilizing effect, while the elongation can be either stabilizing or destabilizing, depending on the poloidal wavelength of the mode and other parameters. It is shown that a low aspect ratio enhances the stabilizing effect of elongation, and weakens its destabilizing effect as well.

Preparation of multi-walled carbon nanotube-reinforced TiNi matrix composites from elemental powders by spark plasma sintering

Carbon nanotube (CNT)-reinforced TiNi matrix composites were synthesized by spark plasma sintering (SPS) employing elemental powders.The phase structure,morphology and transformation behaviors were studied.It was found that thermoelastic martensitic transformation be-haviors could be observed from the samples sintered above 800 ℃ even with a short sintering time (5min),and the transformation tempera-tures gradually increased with increasing sintering temperature because of more Ti-rich TiNi phase formation.Although decreasing the sin-tering temperature and time to 700 ℃ and 5min could not protect defective MWCNTs from reacting with Ti,still-perfect MWCNTs re-mained in the specimens sintered at 900 ℃.This method is expected to supply a basis for preparing CNT-reinforced TiNi composites.

Microstructure and corrosion behavior of NiTi shape memory alloys sintered in the SPS process

NiTi shape memory alloys(SMAs) was developed using the spark-plasma sintering(SPS) process with different average particle size(45 μm and 10 μm) under various temperature. The influence of particle size and temperature on the density, microstructure, and corrosion behavior of the NiTi in simulated body fluid was examined. The porosity decreased with increasing sintering temperature and decreasing particle size, which resulted in an increase in density of the alloy. Increasing the sintering temperature led to the formation of Ni-and Ti-rich intermetallic such as Ni3Ti and NiTi2. The formation of these secondary phases influenced the corrosion behavior of NiTi by changing its chemical composition. The planar structure of NiTi was transformed into a dendritic structure at 900℃, which resulted in the formation of uniform oxide and phosphate layers on the entire surface. A high corrosion potential and low corrosion current density were achieved with NiTi prepared with 10 μm particles at 900℃, which exhibited superior corrosion resistance.

Influence of Surface Radius Curvature on Laser Plasma Propulsion with Ablation Water Propellant

The surface shape of liquid water is well controlled during nanosecond pulse laser ablation plasma propulsion. In this study, we measured the effect of the shape on the coupling coefficient and the specific impulse. We found that the coupling coefficient and specific impulse could be optimized by varying the surface convexity. Based on the analysis of the surface radius curvature, we demonstrate that the convex surface changes the laser focal positions to achieve high efficiency.