The impact of toroidal mode coupling on high-density discharges in J-TEXT
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Peng DENG,
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Wenzhe MAO,
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Zhipeng CHEN,
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Yinan ZHOU,
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Peng SHI,
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Zhoujun YANG,
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Li GAO,
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Tao LAN,
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Jinlin XIE,
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Hong LI,
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Zian WEI,
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Adi LIU,
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Chu ZHOU,
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Weixing DING,
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Wandong LIU,
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Ge ZHUANG
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Abstract
Density limit has long been a widely studied issue influencing the operating range of tokamaks. The rapid growth of the m/n = 2/1 (where m and n are poloidal and toroidal mode numbers, respectively) tearing mode is generally regarded as a primary precursor to the density limit disruption. In this experiment, the coupling of the m/n = 1/1 mode and the m/n = 2/1 mode in high-density plasma was observed. During a sawtooth cycle, the frequencies of the two modes gradually converge until they become equal. After that, toroidal coupling occurs between the 1/1 and 2/1 modes, resulting in a mutually fixed phase relationship. With the occurrence of toroidal coupling, the 2/1 mode is stabilized. Prior to the disruption, the cessation of the 1/1 and 2/1 mode coupling, along with the rapid growth in the amplitude of the 2/1 mode, can be observed. Additionally, under the same parameters, comparing discharges with or without the 1/1 mode, it is found that the presence of the 1/1 mode leads to higher plasma density and temperature parameters.
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