Effective control of intrinsic impurities using n = 1 resonant magnetic perturbation (RMP) in EAST H-mode plasma
Year: 2024
Type: article
Abstract: • RMP significantly reduces tungsten accumulation and decontaminates up to 70%, critical for high-confinement plasmas. • Formation of impurity screening layer observed with increasing I RMP. • RMP’s decontamination effect on impurity is stronger than ELM activity. Since 2021, EAST tokamak has been operated with full tungsten divertors. Tungsten accumulation has been frequently observed in NBI-heated H-mode discharges, resulting in the degradation of plasma confinement performance. Control of tungsten impurity is thus critical for the maintenance of high-confinement plasmas. In this work the impact of the n = 1 resonant magnetic perturbation (RMP) on the behavior of intrinsic low- and high-Z impurities in EAST H-mode discharges are experimentally studied, utilizing high-performance extreme ultraviolet spectroscopic diagnostics. In the dedicated discharge, ELM mitigation, ELM suppression, H-L back transition, RMP penetration occurs in succession with increasing RMP current ( I RMP ). When I RMP is below the threshold for H-L back transition, I RMP_H-L = 2.29 kA, increasing influx of C 2+ and C 3+ ions and decreasing influx of C 4+ and C 5+ ions are observed simutaneously with enhancement of the RMP field. This opposite time behavior in the influx of C 4+ and C 3+ ion is then observed to be magnified during the RMP penetration phase. It indicates a impurity screening layer formed between the locations where C 4+ and C 3+ ions distribute during RMP application based on our previous analysis (W.M. Zhang et al 2024 Nucl. Fusion 64 086004). A large step of increase in C 4+ influx after H-L back transition indicates C 4+ ion mainly located at bottom of pedestal. A higher RMP coil currents threshold capable of impurity screening is found for high-Z impurity ions of Cu 25+ , Mo 30+ , W 42+ , i. e. 0.53–0.75 kA, than that for C 4+ and C 5+ , i. e. 0.33 kA. Meanwhile, it is found that comparing to C 4+ and C 5+ ions the decontamination effect by this impurity screening layer is more efficient for these high-Z impurity ions in plasma core region, e.g. up to 70 % reduction in the impurity density, leading to a significant reduction of radiation power. Furthermore, the continuous reduction of core high-Z impurities level both in ELM mitigation and suppression phase proved that this impurity decontamination effect by RMP field is dominant over the impact of ELM activity to core high-Z impurities transport since tungsten is frequently observed to accumulate during original ELM-free phase. Experimental results from this work would contribute to further understanding of the underlying mechanism how the RMP field impacts the impurity transport.
Source: Nuclear Materials and Energy
Institutions: University of Science and Technology of China, Chinese Academy of Sciences, Hefei Institutes of Physical Science, Institute of Plasma Physics, National Institute for Fusion Science, University of California, Los Angeles, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad de Buenos Aires, Institute of Astronomy and Space Physics
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,840
OpenAlex ID: W4404654405