偏滤器运行模式对托卡马克边缘区等离子体平行流的影响

我们使用一维流体模型,根据在不同偏滤器运行模式下静压强沿着磁力线方向的分布变化,讨论了偏滤器运行模式对托卡马克边缘区等离子体平行流的影响.低再循环模式下,静压强从X点 (X-point)附近的刮削层区域开始明显下降,变化趋势与密度变化趋势一致;等离子体平行流的马赫数在偏滤器区域逐步变大,变化从平缓到迅速.高再循环模式下,静压强在靶板附近的区域迅速下降,在其他区域变化非常小;等离子体平行流的马赫数仅在靠近靶板附近的区域迅速变大,在其他区域变化平缓.在弱脱靶模式下的静压强变化与高再循环模式下类似,不过静压强在X-point附近的刮削层区域开始出现下降的趋势,导致等离子体平行流的马赫数在X-point处的值比在高再循环模式下大.强脱靶模式下,静压强在刮削层区域开始明显下降,在远离靶板的偏滤器区域,静压强迅速下降的地方,观察到高马赫数等离子体平行流.静压强迅速下降引起动压强迅速上升来维持总的压强守恒是在强脱靶状态 下产生高马赫数平行流的一种可能驱动机理.     

Numerical analysis of high Mach flow and flow reversal in the experimental advanced superconducting tokamak divertor

The B2-Eirene (SOLPS 4.0) code package is used to investigate the plasma parallel flow, i.e., the scrape-off layer (SOL) flow, in the experimental advanced superconducting tokamak (EAST) divertor. Simulation results show that the SOL flow in the divertor region can exhibit complex behaviour, such as a high Mach flow and flow reversal in different plasma regimes. When the divertor plasma is in the detachment state, the high Mach flow with approaching or exceeding sonic speed is observed away from the target plate in our simulation. When the divertor plasma is in the high recycling state, the flow reversal with a small Mach number (|M|< 0.2) is observed near the X-point along the separatrix region. The driving mechanisms for the high Mach flow and the reversed flow are analysed theoretically through momentum and continuity equations, respectively. The profile of the ionization sources is shown to be a possible formation condition causing the complex behaviour of the SOL flow. In addition, the effects of the high Mach flow and the flow reversal on the impurity transport are also discussed in this paper.     

Dust charging and levitating in a sheath of plasma containing energetic particles

The structure of the sheath in the presence of energetic particles is investigated in the multi-fluid framework. Based on the orbital motion limited(OML) theory, the dust grain charging inside the sheath of plasma containing energetic particles is examined for the carbon wall, and then the effect of the energetic particles on the stationary dust particle inside the sheath is discussed through the trapping potential energy. It is found that with the increase of energetic ion concentration or energy,the size of dust staying in levitation equilibrium decreases and the levitating position is much closer to the wall. In the case of deuterium ions as energetic ions, the bigger dust particle can be trapped by the sheath than in the case of hydrogen ions as energetic ions. When the energetic electron component is present, the levitating position of dust particle in the sheath depends strongly on the energetic electron. The levitating dust particle is closer to the wall as the energetic electron energy or concentration is increased. In addition, with the increase of temperature of thermal background ion, the size of dust particle trapped by the sheath decreases and the levitating positions of dust particles with the same size radius inside the sheath move toward the wall. Our results can be helpful in investigating the property of the sheath where the energetic particle component is present.     

Sheath structure in plasma with two species of positive ions and secondary electrons

The properties of a collisionless plasma sheath are investigated by using a fluid model in which two species of positive ions and secondary electrons are taken into account. It is shown that the positive ion speeds at the sheath edge increase with secondary electron emission(SEE) coefficient, and the sheath structure is affected by the interplay between the two species of positive ions and secondary electrons. The critical SEE coefficients and the sheath widths depend strongly on the positive ion charge number, mass and concentration in the cases with and without SEE. In addition, ion kinetic energy flux to the wall and the impact of positive ion species on secondary electron density at the sheath edge are also discussed.     

���ŵ���������Ӱ�����ֵ����

通过求解二维热输运方程,数值分析了横越单磁岛的热输运现象。仅有背景加热时,当磁岛宽度小于临界磁岛宽度时,磁岛对能量约束影响不明显;当磁岛宽度大于临界磁岛宽度时,磁岛降低的能量损失随着磁岛宽度呈线性增大,有效径向热导系数在磁岛区域呈高斯分布且最大值在有理面处。当等离子体背景加热与ECRH共同加热时,ECRH对磁岛区域的温度分布及能量约束均有别于背景热源,这为进一步研究ECRH抑制撕裂模的问题提供了基础。