The quasi-coherent signature of enhanced Dα H-mode in Alcator C-Mod
The quasi-coherent signature of enhanced Dα H-mode in Alcator C-Mod
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DOI：
10.1088/0741-3335/43/4/101
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发表时间：
2001-04
影响因子：
2.2
通讯作者：
J. Snipes;B. LaBombard;M. Greenwald;I. Hutchinson;J. Irby;Yi-bing Lin;A. Mazurenko;M. Porkolab
中科院分区：
文献类型：
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作者：
J. Snipes;B. LaBombard;M. Greenwald;I. Hutchinson;J. Irby;Yi-bing Lin;A. Mazurenko;M. Porkolab
在激励器C模中发现的中到高密度的稳态H模，称为增强型Dα(EDA)H模，似乎是由陡峭边缘梯度区的连续准相干(QC)模维持的。QC模式驱动的是典型频率约为100 kHz的大幅度密度和磁涨落。通过插入一个包含两个极向分离的朗缪尔探头和一个极向场拾取线圈的快速扫描探头，在陡峭的边缘梯度区域测量这些波动。当探头接近等离子体边缘时，在最后闭合的磁通面(LCFS)约2厘米范围内测量到明显的磁涨落。模的幅度随离等离子体中心的距离迅速下降，其指数衰减长度为KR≈1.5 cm-1，在外侧中面以上10 cm处测得。密度起伏外推的均方根幅度为θ≈5 G。而朗缪尔探头上的密度起伏只有在距离Lcfs几毫米的范围内才可见。在QC模式频率下，势能和密度涨落充分同位相以增强粒子的输运。这些结果表明，EDA H模的QC特征是一种电磁模式，它似乎是导致等离子体边缘粒子输运增强的原因。
The steady-state H-mode regime found at moderate to high density in Alcator C-Mod, known as enhanced Dα (EDA) H-mode, appears to be maintained by a continuous quasi-coherent (QC) mode in the steep edge gradient region. Large amplitude density and magnetic fluctuations with typical frequencies of about 100 kHz are driven by the QC mode. These fluctuations are measured in the steep edge gradient region by inserting a fast-scanning probe containing two poloidally separated Langmuir probes and a poloidal field pick-up coil. As the probe approaches the plasma edge, clear magnetic fluctuations were measured within about 2 cm of the last-closed flux surface (LCFS). The mode amplitude falls off rapidly with distance from the plasma centre with an exponential decay length of kr≈1.5 cm-1, measured 10 cm above the outboard midplane. The root-mean-square amplitude of the fluctuation extrapolated to the LCFS was θ≈5 G. The density fluctuations, on the other hand, were visible on the Langmuir probe only when it was within a few millimetres of the LCFS. The potential and density fluctuations were sufficiently in phase to enhance particle transport at the QC mode frequency. These results show that the QC signature of the EDA H-mode is an electromagnetic mode that appears to be responsible for the enhanced particle transport in the plasma edge.