The role of shear flow collapse and enhanced turbulence spreading in edge cooling approaching the density limit
- Long, Ting;
- Diamond, PH;
- Ke, Rui;
- Chen, Zhipeng;
- Xu, Xin;
- Tian, Wenjing;
- Hong, Rongjie;
- Cao, Mingyun;
- Liu, Yanmin;
- Xu, Min;
- Wang, Lu;
- Yang, Zhoujun;
- Yuan, Jinbang;
- Zhou, Yongkang;
- Yan, Qinghao;
- Yang, Qinghu;
- Shen, Chengshuo;
- Nie, Lin;
- Wang, Zhanhui;
- Hao, Guangzhou;
- Wang, Nengchao;
- Chen, Zhongyong;
- Li, Jiquan;
- Chen, Wei;
- Zhong, Wulyu
Published Web Location
https://doi.org/10.1088/1741-4326/ad3e15Abstract
Experimental studies of the dynamics of shear flow and turbulence spreading at the edge of tokamak plasmas are reported. Scans of line-averaged density and plasma current are carried out while approaching the Greenwald density limit on the J-TEXT tokamak. In all scans, when the Greenwald fraction f G = n ¯ / n G = n ¯ / ( I p / π a 2 ) increases, a common feature of enhanced turbulence spreading and edge cooling is found. The result suggests that turbulence spreading is a good indicator of edge cooling, indeed better than turbulent particle transport is. The normalized turbulence spreading power increases significantly when the normalized E × B shearing rate decreases. This indicates that turbulence spreading becomes prominent when the shearing rate is weaker than the turbulence scattering rate. The asymmetry between positive/negative (blobs/holes) spreading events, turbulence spreading power and shear flow are discussed. These results elucidate the important effects of interaction between shear flow and turbulence spreading on plasma edge cooling.
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