4.5 Article

Plasma performance improvement with favourable Bt relative to unfavourable Bt in RF-heated H-mode plasmas in EAST

Journal

NUCLEAR FUSION
Volume 61, Issue 2, Pages -

Publisher

IOP PUBLISHING LTD
DOI: 10.1088/1741-4326/abcb27

Keywords

plasma performance improvement; favourable toroidal field; EAST; lower hybrid wave (LHW)

Funding

  1. National Natural Science Foundation of China [12005257, 11675220, 11705237, 11975276, 11922513, 11905143]
  2. K.C. Wong Education Foundation
  3. Key Research Program of Frontier Sciences, CAS [QYZDB-SSWSLH001]
  4. CASHIPS Director's Fund [YZJJ2020QN13]
  5. Anhui Provincial Natural Science Foundation [2008085J04]
  6. Special Research Assistant Funding of CAS
  7. China Postdoctoral Science Foundation [2020M671913]

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The study found that in the EAST tokamak, plasma with favorable toroidal field B-t exhibited higher core electron temperature and steeper pedestal density, with the improvement in plasma performance mainly contributed by the increase of core electron temperature. Additionally, the plasma with favorable B-t had lower density and recycling in the scrape-off layer, which further aided in mitigating parametric instability activity and increasing core electron temperature.
Significant improvement of plasma performance in high-confinement mode (H-mode) discharges with favourable toroidal field B-t, i.e. the ion backward difference B drift towards the primary X-point, has been widely observed in the EAST tokamak with pure radio-frequency heating in contrast to that with the unfavourable B-t. Statistical analysis indicates that plasma in the favourable B-t has higher core electron temperature, similar core ion temperature and relatively steeper pedestal density compared with that in the unfavourable B-t. The improvement in plasma performance is mainly contributed by the increase of core electron temperature in the favourable B-t. Further analysis indicates that the plasma with favourable B-t has much lower density and recycling in the scrape-off layer (SOL). Lower SOL density and recycling benefit the mitigation of parametric instability activity of lower hybrid wave (LHW), and thus facilitate the increase of core electron temperature in the favourable B-t. The performance improvement in the favourable B-t demonstrates to be more evident with high LHW power. Divertor local E-r x B drift which can increase the backflow particles from the divertor region to the upstream region could be partly responsible for the much higher SOL plasma density in unfavourable B-t. These findings could facilitate the application of LHW power on future large fusion devices, such as the China Fusion Engineering Test Reactor, to achieve high-performance steady-state operation.

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