TY  - JOUR
AU  - Sun, H. J.
AU  - Goldston, R. J.
AU  - Huber, A.
AU  - Xu, X. Q.
AU  - Flanagan, J.
AU  - McDonald, D. C.
AU  - de la Luna, E.
AU  - Maslov, M.
AU  - Harrison, J. R.
AU  - Militello, F.
AU  - Fessey, J.
AU  - Cramp, S.
TI  - The role of edge plasma parameters in H-mode density limit on the JET-ILW
JO  - Nuclear fusion
VL  - 61
IS  - 6
SN  - 0029-5515
CY  - Vienna
PB  - IAEA
M1  - FZJ-2021-05646
SP  - 066009 -
PY  - 2021
AB  - 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, ν∗,SOL increases, SOL broadens, Er shear decreases, triggers L-mode; ne drops, ν∗,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.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000645584300001
DO  - DOI:10.1088/1741-4326/abf056
UR  - https://juser.fz-juelich.de/record/904076
ER  -