负径向电场对带电粒子俘获率影响的数值模拟

本文采用数值方法求解Grad-Shafranov方程反演EAST典型长脉冲放电实验(炮号33068)的平衡位形和磁场分布,进而结合粒子在托卡马克电磁场中的运动方程,模拟氘离子在负径向电场存在时的运动轨迹,并统计不同负径向电场下的氘离子俘获率。结果表明:随负径向电场的增大,氘离子轨迹由扩张通行轨迹向外翻香蕉轨迹再向内翻香蕉轨迹,最后向压缩通行轨迹演变;氘离子俘获率随负径向电场的增大而减小,氘离子初始速度越小,其变化越大。     

等离子体电流反向平衡位形中带电粒子运动的数值模拟研究

本文采用数值方法求解Grad-Shafranov方程获得CT-6B交流放电实验总电流过零时的平衡位形和磁场分布,进而结合粒子在磁场中的运动方程,模拟氘离子在该平衡位形中的运动轨迹,统计氘离子的损失率与损失位置。结果表明：总电流过零时刻的平衡位形为内外两侧电流反向平衡位形,在强、弱场侧各存在1个磁岛,电流在磁岛附近取极值;位于强场侧的粒子几乎不损失,弱场侧的粒子在径向位置很大时存在损失,越靠近边界损失率越高;损失位置基本上位于赤道面以下并在最底部达到极值;随初始角变大,氘离子轨迹由通行轨迹变成损失轨迹再向香蕉轨迹演变。     

漂移热流与托卡马克等离子体径向箍缩

考虑到俘获粒子的极向分布不均匀性,在研究可能的等效外场引起的径向输运时,本文分析了漂移热流的影响。由于磁场的不均匀性,漂移热流可使磁面上离子平衡温度不再为常量,从而导致沿磁力线方向静电场的出现。当考虑到俘获粒子效应时,这种沿磁力线电场引起的粒子径向箍缩是一种新经典类型的箍缩机制。在反磁剪切引起的势垒处,由于温度梯度特别大,这一箍缩效应极为强烈,这有助于解释此处输运好于新经典输运的原因。     

径向电场中带电粒子束的质量分离

带电粒子束已广泛应用于科学、工程和国民经济的诸多领域,而质量色散及分离是电磁质量分离器和谱仪等领域中的关键科学问题。本文推导离子束流在径向电场中的运动轨迹解析表达式,应用MATLAB模拟特征质量离子的聚焦轨迹。从轨迹图中可看出,不同质量离子在径向电场中按质量聚焦,具有明显的分离效果。本文的研究结果为等离子体光学质量分离装置的研制奠定了理论基础,同时对于特殊位形电磁场控制带电粒子束等相关领域的研究具有一定的借鉴意义。     

低真空中SPIG性能的蒙特卡罗模拟研究

应用蒙特卡罗技术对低真空中六极离子导向器的性能进行了计算机模拟研究。模拟计算跟踪每个离子的轨迹直至它逃离感兴趣的区域或达到终点。离子在低真空六极射频电场中受到来自电场和剩余气体两方面的作用力，这两个力对离子的运动影响在模拟中分开计算。前者用龙格－库塔方法求解运动微分方程，后者体现为离子与气体分子之间的两体撞，ＲＳ模型和ＭＳＷ模型用于计算碰撞过程。     

TFTR反向剪切等离子体的极向旋转

在托卡马克聚变试验反应堆中观测到，芯部碳杂质离子的极向旋转的分叉出现在与进增强反向剪切等离子体相关系的运分叉前，在等离子体的狭窄径向区域，杂质离子的极向极向旋转反向，这个极向流与一个具有强剪切的大径向电场的建立相联系。在这个先兆之前、之中和之后测得的极向速度与新经典的推测不同。     

SIMS对氘靶钛膜中氘的分布研究

用负的ＳＩＭＳ分析技术进行Ｈ同位素相对含量Ｔｉ膜深度变化的分析，获得了氘随膜深度变化的分布曲线。在接近膜表面的一个深度范围内，除有明显的Ｏ＾－、ＣＯ＾－和很微弱的ＯＨ＾－，ＯＤ＾－及ＣＨＯ＾－峰谱外，还有很大的Ｄ＾－二次离子质谱峰，氘的丰度估计约为９８％。在靶膜内部，氘的丰度达９９％以上。     

电子回旋波在非圆截面托卡马克等离子体中的传播与功率沉积

通过求解等离子体平衡方程、波迹方程和准线性Fokker-Planck方程,数值模拟了电子回旋(EC)波在非圆截面托卡马克等离子体中的传播轨迹和功率沉积。模拟结果表明:当EC波从顶部发射时,相比于圆截面的EC波波迹,非圆截面的波迹会向等离子体弱场侧偏移,增大等离子体中心电子密度,波迹也会偏向弱场侧,相应的波功率沉积有所降低;当EC波O模从中平面弱场侧发射时,随着平行折射率的增大,波迹弯曲幅度变大,增大到一定数值时会折回弱场侧穿出,波功率沉积随极向发射角的增大而降低,环向发射角约取10°时,波功率沉积达到最大。     

高流速下钯上氢氘的排代研究

在钯氘化物上进行了高流速下氢氘的排代实验。结果表明，氘的排代效率随排代时间的增大而增加；与低压、低流速相比，高流速下排代压力的增加部分弥补了流速增大对氢氘交换速率的影响，因此仍可以得到较高的氘回收率。     

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。     

Effects of resonant magnetic perturbations on the loss of energetic ions in tokamak pedestal

Resonant magnetic perturbations (RMPs) are extensively applied to mitigate or suppress the edge localized mode in tokamak plasmas, but will break the axisymmetric magnetic field configuration and increase the loss of energetic ions. The mechanism of RMPs induced energetic ion loss has been extensively studied, and is mainly attributed to resonant effects. In this paper, in the perturbed non-axisymmetric tokamak pedestal, we analytically derive the equations of guiding center motion for energetic ions including the bounce/transit averaged radial drift velocity and the toroidal precession frequency modified by strong radial electric field. The loss time of energetic ions is numerically solved and its parametric dependence is analyzed in detail. We find that passing energetic ions cannot escape from the plasma, while deeply trapped energetic ions can escape from the plasma. The strong radial electric field plays an important role in modifying the toroidal precession frequency and resulting in the drift loss of trapped energetic ions. The loss time of trapped energetic ions is much smaller than the corresponding slowdown time in DIII-D pedestal. This indicates that the loss of trapped energetic ions in the perturbed non-axisymmetric pedestal is important, especially for the trapped energetic ions generated by perpendicular neutral beam injection.     

Symplectic Simulations of Radial Diffusion of Fast Alpha Particles in the Presence of Low-Frequency Modes in Rippled Tokamaks

The symplectic Hamiltonian guiding centre code which enables efficient calculation of charged particle trajectories and diffusion coefficients has been applied to fast ion motion in magnetically perturbed tokamak plasmas. Particularly fusion born alpha particle drift motion, in constant of motion space, is examined in the presence of low mode-number neoclassical tearing mode (NTM) perturbation in a toroidally rippled tokamak. The main focus of this study is to investigate the dependence of the radial diffusion coefficient of energetic ions on the perturbation strength and on the localization of the perturbation. The resonance between bounce motion and toroidal field ripples plays a significant role in this context. The presence of NTMs results in substantial enhancement of radial diffusion coefficient for passing particles. Depending on the strength and localization of the NTM it can cause enhancement or degradation of the radial ripple diffusion coefficient of trapped particles.     

Radial Electric Field and its Influence on Poloidal Magnetic Field Oscillations in the IR-T1 Tokamak

The radial electric field has been investigated in the edge plasma of IR-T1 tokamak by movable sets of single Langmuir probes. Simultaneous measurements of the radial electric field and poloidal magnetic field oscillations shown that magnetohydrodynamics activity is damped when the radial electric field becomes more negative in the plasma edge. The results shown that MHD frequency decreases while the radial electric field increasing negatively.     

An experimental apparatus proposed for efficient removal of isobaric contaminants in negative ion beams

Isobaric contaminants are often problematical in accelerated negative ion beams for research at certain radioactive ion beam (RIB) and accelerator mass spectrometry (AMS) facilities since their presence in low-intensity rare isotopic beams seriously compromise experimental results. This article describes a non-resonant, laser-based photo-detachment apparatus for use at these facilities, which, according to calculations efficiently removes isobaric contaminants from these beams. The advantage of the system for isobaric contaminant removal over other systems proposed to date lies in its ability to efficiently capture easily transportable energetic negative ion beams with low, intermediate or high energy spreads by a superconducting solenoid magnetic field. The ability to change the diameter of captured beams by adjusting the magnetic field strength permits optimum control of the radial overlap of the laser/negative ion beam profiles over an extended interaction region under high vacuum conditions without retarding optical affect, collision-cooling or capture losses.     

Effects of Magnetic Field and Ion Velocity on SPT Plasma Sheath Characteristics

The distribution of magnetic field in Hall thruster channel has significant effect on its discharge process and wall plasma sheath characteristics. By creating physical models for the wall sheath region and adopting two-dimensional particle in cell simulation method, this work aims to investigate the effects of magnitude and direction of magnetic field and ion velocity on the plasma sheath characteristics. The simulation results show that magnetic field magnitudes have small impact on the sheath potential and the secondary electron emission coefficient, magnetic azimuth between the magnetic field direction and the channel radial direction is proportional to the absolute value of the sheath potential, but inversely proportional to the secondary electron emission coefficient. With the increase of the ion incident velocity, secondary electron emission coefficient is enhanced, however, electron density number, sheath potential and radial electric field are decreased. When the boundary condition is determined, with an increase of the sinmlation area radial scale, the sheath potential oscillation is aggravated, and the stability of the sheath is reduced.     

Simulation of the Radial Electric Field in the Small Size Divertor Tokamak for Discharge with Neutral Beam Injection (NBI)

The radial electric field in the edge plasma of small size divertor tokamak can be simulated by B2SOLPS0.5.2D fluid transport code. The simulation provides the follow results: (1) Switching on and off the part of the parallel plasma viscosity driven by parallel ion diamagnetic heat flux (Bekheit in J. Fusion Energ 27(4), 338–345, 2008; Schneider et al. in Nucl. Fusion 41:387, 2001) and Counter-NBI plasma heating change profile of radial electric field significantly. (2) Switching on and off the parallel plasma viscosity driven by parallel ion diamagnetic heat flux leads to the radial electric field is toroidal magnetic field dependence (3) For the case of counter-NBI plasma heating, the switching on and off the current driven by part parallel plasma viscosity depends on the ion diamagnetic heat flux leads to the ion poloidal velocity is toroidal magnetic field B_T dependence. (4) The profile of the radial electric field in edge plasma of small size divertor tokamak is consistent with poloidal rotation velocity.     

Effects of trapped electrons on the ion temperature gradient mode in tokamak plasmas with hollow density profiles

The ion temperature gradient(ITG) mode in the presence of impurity ions and trapped electrons(TEs) is numerically investigated in tokamak plasmas with hollow density profiles, using the gyrokinetic integral eigenmode equation. It is found that in the inverted density plasma, the increase of the ITG enhances the growth rate and frequency of the ITG, and the density gradient plays an important role in the ITG modes. For weak density gradient situations, the trapped electron effects increase the instability of the ITG, while the impurity has an obviously stabilizing effect. For the strong density gradient cases, both the impurities and trapped electrons enhance the ITG instabilities. In addition, it is shown that the growth rate of the ITG decreases with positive magnetic shear s while the real frequency increases with positive magnetic shear.The growth rate of the ITG increases with negative magnetic shear s while the real frequency decreases with negative magnetic shear. The length of the calculated mode structure in the positive and negative magnetic shear intervals is also presented.     

Influence of magnetic filter field on the radio-frequency negative hydrogen ion source of neutral beam injector for China Fusion Engineering Test Reactor

In the design of negative hydrogen ion sources,a magnetic filter field of tens of Gauss at the expansion region is essential to reduce the electron temperature,which usually results in a magnetic field of around 10 Gauss in the driver region,destabilizing the discharge.The magnetic shield technique is proposed in this work to reduce the magnetic field in the driver region and improve the discharge characteristics.In this paper,a three-dimensional fluid model is developed within COMSOL to study the influence of the magnetic shield on the generation and transport of plasmas in the negative hydrogen ion source.It is found that when the magnetic shield material is applied at the interface of the expansion region and the driver region,the electron density can be effectively increased.For instance,the maximum of the electron density is 6.7×1017 m-3 in the case without the magnetic shield,and the value increases to 9.4×1017 m-3 when the magnetic shield is introduced.