The impact of ELM mitigation on tungsten source in the EAST divertor
- 15 February 2021
- journal article
- research article
- Published by IOP Publishing in Nuclear Fusion
- Vol. 61 (4), 046046
- https://doi.org/10.1088/1741-4326/abe697
Abstract
Divertor tungsten (W) erosion source during edge localized mode (ELM) bursts in EAST is investigated based on optical emission spectroscopy on atomic neutral tungsten line emission at 400.9 nm. Both temporal evolution and total source strength are analyzed and compared in three different ELM mitigation schemes including natural ELMs, resonant magnetic perturbations (RMP) and 2.45 GHz lower hybrid wave (LHW). The mitigation of W source at divertor target caused by single ELMs is mainly attributed to the reduction of the W source production in the ELM decay phase. However, with the increase of ELM frequency, the time-averaged intra-ELM W source during an ELM cycle rises and dominates the evolution of the total W source with increasing fraction, which could be related to the increase of the core W level. In the natural ELM scheme, the pedestal electron temperature is found not only to control the effective W sputtering yield at target during ELMs, thus influencing the intra-ELM W source, but also to be related to the delay time between the divertor ELM WI emission and the core extreme ultraviolet bolometer (XUV) signal which can scale with the parallel ion transit time. Furthermore, the delay time is found to have more consistent dependence on the pedestal plasma collisionality. The rise time of ELM WI emission intensity increases when RMP or LHW is applied, revealing the different ELM mitigation mechanisms from the natural ELM scheme. The temporal profiles of ELM WI emission in different ELM mitigation schemes are compared and the potential mechanism is discussed. Besides, the ELM mitigation effects with RMP are found to be asymmetric at the outer and inner divertor targets, which is characterized by the different changes in the W source strength and the rise time with the ramp-up of RMP coil current. Divertor partial detachment is achieved simultaneously with strong ELM mitigation under a suitable RMP phase difference without additional gas puff.Keywords
Funding Information
- K. C. Wong Education Foundation, CASHIPS Director’s Fund (BJPY2019A01)
- Key Research Program of Frontier Sciences CAS (QYZDB-SSW-SLH001)
- National Natural Science Foundation of China (11575243 11625524 11875287 11922513 U19A20113)
- National Key Research and Development Program of China (2017YFA0402500 2017YFE0301300 2018YFE0303103)
- SINO-GERMAN project by the Deutsche Forschungsgemeinschaft and the National Natural Science Foundation of China (11861131010)
- Users with Excellence Project of Hefei Science Center CAS (2018HSC-UE008 2018HSC-UE010)
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