The role of shear flow collapse and enhanced turbulence spreading in edge cooling approaching the density limit

Long, Ting; Diamond, P. H.; 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

doi:10.1088/1741-4326/ad3e15

Title: The role of shear flow collapse and enhanced turbulence spreading in edge cooling approaching the density limit

Journal Article · 25 April 2024 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/ad3e15 · OSTI ID:2341353

;

; Xu, Xin; Tian, Wenjing;

;

; Liu, Yanmin; Xu, Min;

;

; Zhou, Yongkang; Yan, Qinghao; Yang, Qinghu; Shen, Chengshuo; Nie, Lin; Wang, Zhanhui;

Abstract 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 $f_{G} = \bar{n} / n_{G} = \bar{n} / (I_{p} / π a^{2})$ 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 $E \times B$ 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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Sponsoring Organization:: USDOE

Grant/Contract Number:: FG02-04ER54738

OSTI ID:: 2341353

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 6 Vol. 64; ISSN 0029-5515

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: IAEA

Language:: English

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