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| Home > Publications database > Investigation of divertor W source and its control in EAST H mode plasmas |
| Abstract | FZJ-2021-01670 |
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2021
Abstract: Investigation of divertor W source and its control in EAST H mode plasmas F. Ding1*, X. H. Chen1, L. Wang1, R. Ding1, S. Brezinsek2, L. Zhang1, Z. H. Hu1, Q. Zhang1, Q. Ma1, D.W. Ye1, Y. Luo1, Z.T. Zhang1, Y. W. Sun1, G.-N. Luo1 and the EAST team1 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China 2 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung—Plasmaphysik,Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany*E-mail: fding@ipp.ac.cnAn effective control of W erosion at the wall is not only a concern for the lifetime of Plasma-facing Material (PFM), but also a prerequisite for maintaining a low W concentration in the plasma core. In high confinement plasma discharges, a large amount of energetic particles in pedestal are ejected onto divertor targets in a timescale less than 1 ms during the burst of edge localized mode (ELM), even penetrating the detached divertor edge and inducing significant W erosion at the divertor targets [1], which contributes most of the W source in H-mode plasma and needs to be well understood and controlled. In EAST, intra-ELM W sources are resolved and studied via photo multiplier tube (PMT) measurements with optical filters. The non-W spectral emissions passing through the narrowband filter were deducted via a cross-calibration with spectrometer system with high spectral resolution. It is observed that the intra-ELM W erosion has a linear dependence on the plasma energy loss during each ELM burst when the carbon content in plasma is maintained at a relatively low level. However, high carbon content in plasma can alter this dependence by inducing stronger W sputtering even with a low ELM energy loss. In helium plasma discharges, the ELM-induced W sputtering behaves more like those in deuterium (D) plasmas with high C content, indicating the effect of main ion mass. ELM frequency effects on divertor W source are addressed in two different regimes, the natural ELMs and the resonant magnetic perturbation (RMP) mitigated ELMs. It is found that intra-ELM W erosion rate with natural ELMs can roll over after a certain ELM frequency, that is, firstly rise and then drop with the increase of ELM frequency, while a continuous growth of intra-ELM W erosion rate is observed with RMP-mitigated ELMs from around 40 Hz to 300 Hz. These should be the major reason for the indistinctive mitigation of total W source, including intra- and inter-ELM W sources, with the increase of ELM frequency Moreover, the asymmetric distribution of W source in the divertor during H mode discharges are investigated both poloidally and toroidally. The ELM burst can induce an obviously stronger W erosion at outer divertor than at inner divertor, which can be influenced by the toroidal magnetic field direction, plasma density as well as the ELM-induced plasma energy loss. The toroidal non-axisymmetric distribution at the outer divertor can be observed by rotating RMP field toroidally, characterized by local W erosion peaks in toroidal direction. The two poloidally separated W sources at the divertor targets exhibit different responses to the neon seeding, mitigated around the strike point, while enhanced in the outer one, which could enhance the leakage of W impurity into main plasma.[1] S. Brezinsek et al., Nucl. Fusion 59, 096035 (2019).
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