Modeling far-field radio-frequency sheaths in Alcator C-Mod
Modeling far-field radio-frequency sheaths in Alcator C-Mod
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在 Alcator C-Mod 中模拟远场射频鞘
DOI：
10.1088/0741-3335/55/8/085001
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发表时间：
2013
影响因子：
2.2
通讯作者：
D. Whyte
中科院分区：
文献类型：
--
作者：
D. D'Ippolito;J. Myra;R. Ochoukov;D. Whyte
最近在离子回旋加速器频率范围（ICRF）加热过程中，在alcatator C-Mod中测量了大（> - 100v）等离子体电位，从而激发了本文的研究。等离子体电位在与限制器相交但不经过供电ICRF天线附近的场线上测量。测量电位与局部ICRF快波电场相关，是导致限制器表面Mo溅射增加的主要候选因素。在本文中，证明了“远场”射频（rf）鞘理论可以定性地解释这一实验观察。该理论描述了当未吸收的快速ICRF波入射到远离天线的导电边界时rf鞘层的形成。结果表明，射频护套驱动对表面法向与平衡磁场之间的夹角敏感。本工作的主要结论是，B场限制器尖端附近几何形状的快速切向变化促进了与测量值相同数量级的大鞘电位的形成。
This paper is motivated by the recent measurement of large (>100 V) plasma potentials in Alcator C-Mod during ion cyclotron range of frequency (ICRF) heating. The plasma potential is measured on field lines that intersect a limiter but do not pass near a powered ICRF antenna. The measured potential correlates with the local ICRF fast wave electric field and is a prime candidate to cause increased Mo sputtering from the limiter surface. In this paper, it is shown that a theory of ‘far-field’ radio-frequency (rf) sheaths can qualitatively explain this experimental observation. The theory describes rf-sheath formation when unabsorbed fast ICRF waves are incident on a conducting boundary far from the antenna. It is shown that the rf-sheath drive is sensitive to the angle between the surface normal and the equilibrium magnetic field. The main conclusion of this work is that the rapid tangential variation in the B field-limiter geometry near the tip of the limiter promotes the formation of large sheath potentials of the same order as the measured ones.