Reciprocating Probe Measurements of L-H Transition in LHCD H-Mode on EAST

As the power available in the initial phase of the ITER operation will be limited, accessing the high confinement mode （H-mode） with low heating power will be a critical issue. In the recent experiment on EAST, the H-mode was obtained for the first time with lower hybrid current drive （LHCD） wave on...

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Published inPlasma science & technology Vol. 15; no. 7; pp. 619 - 622
Main Author 刘鹏 徐国盛 汪惠乾 蒋敏 王亮 张炜 刘少承 颜宁 丁斯晔
Format Journal Article
LanguageEnglish
Published 01.07.2013
Subjects
Dithering
EAST
Electric fields
Electric power generation
Erbium
Heating
H模式放电
LHCD
Oscillations
Reciprocating
Shot
Spikes
低杂波电流驱动
加热功率
国际热核实验堆
朗缪尔探针
测量
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ISSN1009-0630
DOI10.1088/1009-0630/15/7/03

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Summary:As the power available in the initial phase of the ITER operation will be limited, accessing the high confinement mode （H-mode） with low heating power will be a critical issue. In the recent experiment on EAST, the H-mode was obtained for the first time with lower hybrid current drive （LHCD） wave only. Reciprocating Langmuir probe measurements at the outer midplane showed that the electron density ne and electron tempel：ature Te in the scrape-off layer （SOL） were significantly reduced in the ELM-free phase, resulting in the increase of lower-hybrid wave （LHW） reflection. It was found that the power loss Ploss was comparable during the L-H transition, by comparing the adjacent L-mode and H-mode discharge. The Da emission, Te and ne decreased rapidly in the time scale of about 1 ms, and the radial electric field Er turned positive in this process near the last closed flux surface. Multiple L-H-L transitions were observed during a single shot when the applied LHW power was marginal to the threshold. The floating potential （Vf） had negative spikes corresponding with the Da signal, and Er oscillation evolved into several intermittent negative spikes just before the L-H transition. In some shots, dithering was observed just before the L-H transition.
Bibliography:LIU Peng , XU Guosheng , WANG Huiqian , JIANG Min , WANG Liang, ZHANG Wei, LIU Shaocheng , YAN Ning ,DING Siye（1Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China 2Association EURATOM-DTU, Physics Department, DK-4000 Roskilde, Denmark）
As the power available in the initial phase of the ITER operation will be limited, accessing the high confinement mode （H-mode） with low heating power will be a critical issue. In the recent experiment on EAST, the H-mode was obtained for the first time with lower hybrid current drive （LHCD） wave only. Reciprocating Langmuir probe measurements at the outer midplane showed that the electron density ne and electron tempel：ature Te in the scrape-off layer （SOL） were significantly reduced in the ELM-free phase, resulting in the increase of lower-hybrid wave （LHW） reflection. It was found that the power loss Ploss was comparable during the L-H transition, by comparing the adjacent L-mode and H-mode discharge. The Da emission, Te and ne decreased rapidly in the time scale of about 1 ms, and the radial electric field Er turned positive in this process near the last closed flux surface. Multiple L-H-L transitions were observed during a single shot when the applied LHW power was marginal to the threshold. The floating potential （Vf） had negative spikes corresponding with the Da signal, and Er oscillation evolved into several intermittent negative spikes just before the L-H transition. In some shots, dithering was observed just before the L-H transition.
L-H transition, reciprocating probe, dithering
34-1187/TL
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SourceType-Scholarly Journals-1
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ISSN:1009-0630
DOI:10.1088/1009-0630/15/7/03