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  • The role of edge plasma parameters in H-mode density limit on the JET-ILW
    Sun, Hai-Jing ...
    A study of a dataset of JET H-mode plasma with the Be/W ITER-like wall (JET-ILW) shows that reaching the edge MHD ballooning limit leads to confinement degradation. However, unlike JET plasmas with a ... carbon wall (JET-C), the JET-ILW plasmas stay in a marginal dithering phase for a relatively long period, associated with a higher (-20%) H-mode density limit (HDL) than JET-C equivalents. This suggests that ITER could be operated in H-mode with higher density than the scaling based on carbon wall devices, but likely with a dithering phase plasma with lower confinement. A new, reliable estimator for JET Er, min has been derived by combining HRTS measurements of pedestal gradient and edge-SOL decay lengths. JET radial Er ETB wells are observed in the range of -15 to -60 kV m-1 in high performance H-modes, consistent with previous CXRS results in ASDEX Upgrade. The results imply that a higher positive E - B shear in the near SOL plays a role in sustaining a marginal phase in JET-ILW which leads to a higher HDL than that in JET-C. The results of the JET-ILW dataset show agreement with the Goldston finite collisionality HD model for SOL broadening at high collisionality. A hypothesis for the dithering H-mode phase is proposed: as ne,SOL increases, lowast,SOL increases, SOL broadens, Er shear decreases, triggers L-mode; ne drops, lowast,SOL decreases, SOL becomes narrower, and Er shear increases, triggering H-mode, resulting in a cycle of H-L-H- oscillations. For burning plasma devices, such as ITER, operating just below the MHD limit for the dithering phase could be a promising regime for maximising core density, and fusion performance while minimising plasma-material interaction. The oscillatory signal during the dithering phase could be used as a precursor of undesirable plasma performance for control purposes.
    Source: Nuclear fusion. - ISSN 0029-5515 (Vol. 61, Art. 066009, 2021)
    Type of material - article, component part
    Publish date - 2021
    Language - english
    COBISS.SI-ID - 71420163
    DOI

source: Nuclear fusion. - ISSN 0029-5515 (Vol. 61, Art. 066009, 2021)
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