The role of edge plasma parameters in H-mode density limit on the JET-ILW

H. J. Sun; R. J. Goldston; A. Huber; X. Q. Xu; J. Flanagan; D. C. McDonald; E. De La Luna; M. Maslov; J. R. Harrison; F. Militello; J. Fessey; S. Cramp

doi:10.1088/1741-4326/abf056

The role of edge plasma parameters in H-mode density limit on the JET-ILW

H. J. Sun, R. J. Goldston, A. Huber, X. Q. Xu, J. Flanagan, D. C. McDonald, E. De La Luna, M. Maslov, J. R. Harrison, F. Militello, J. Fessey, S. Cramp

Princeton University

Research output: Contribution to journal › Article › peer-review

Abstract

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 E r, min has been derived by combining HRTS measurements of pedestal gradient and edge-SOL decay lengths. JET radial E r 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 n e,SOL increases, ν ∗,SOL increases, SOL broadens, E r shear decreases, triggers L-mode; n e drops, ν ∗,SOL decreases, SOL becomes narrower, and E r 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.

Original language	American English
Article number	066009
Journal	Nuclear Fusion
Volume	61
Issue number	6
DOIs	https://doi.org/10.1088/1741-4326/abf056
State	Published - Jun 2021

ASJC Scopus subject areas

Nuclear and High Energy Physics
Condensed Matter Physics

Keywords

H-mode density limit
JET-ILW
SOL decay length
edge ballooning limit
radial electrical field

Access to Document

10.1088/1741-4326/abf056

Cite this

@article{6cba0cae2bef4c64b4a62d578dcf022f,

title = "The role of edge plasma parameters in H-mode density limit on the JET-ILW",

abstract = "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 E r, min has been derived by combining HRTS measurements of pedestal gradient and edge-SOL decay lengths. JET radial E r 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 n e,SOL increases, ν ∗,SOL increases, SOL broadens, E r shear decreases, triggers L-mode; n e drops, ν ∗,SOL decreases, SOL becomes narrower, and E r 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.",

keywords = "H-mode density limit, JET-ILW, SOL decay length, edge ballooning limit, radial electrical field",

author = "Sun, {H. J.} and Goldston, {R. J.} and A. Huber and Xu, {X. Q.} and J. Flanagan and McDonald, {D. C.} and {De La Luna}, E. and M. Maslov and Harrison, {J. R.} and F. Militello and J. Fessey and S. Cramp",

note = "Publisher Copyright: {\textcopyright} EURATOM 2021.",

year = "2021",

month = jun,

doi = "10.1088/1741-4326/abf056",

language = "American English",

volume = "61",

journal = "Nuclear Fusion",

issn = "0029-5515",

publisher = "IOP Publishing Ltd.",

number = "6",

}

TY - JOUR

T1 - The role of edge plasma parameters in H-mode density limit on the JET-ILW

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.

PY - 2021/6

Y1 - 2021/6

N2 - 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 E r, min has been derived by combining HRTS measurements of pedestal gradient and edge-SOL decay lengths. JET radial E r 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 n e,SOL increases, ν ∗,SOL increases, SOL broadens, E r shear decreases, triggers L-mode; n e drops, ν ∗,SOL decreases, SOL becomes narrower, and E r 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.

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 E r, min has been derived by combining HRTS measurements of pedestal gradient and edge-SOL decay lengths. JET radial E r 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 n e,SOL increases, ν ∗,SOL increases, SOL broadens, E r shear decreases, triggers L-mode; n e drops, ν ∗,SOL decreases, SOL becomes narrower, and E r 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.

KW - H-mode density limit

KW - JET-ILW

KW - SOL decay length

KW - edge ballooning limit

KW - radial electrical field

UR - http://www.scopus.com/inward/record.url?scp=85105966728&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85105966728&partnerID=8YFLogxK

U2 - 10.1088/1741-4326/abf056

DO - 10.1088/1741-4326/abf056

M3 - Article

SN - 0029-5515

VL - 61

JO - Nuclear Fusion

JF - Nuclear Fusion

IS - 6

M1 - 066009

ER -

The role of edge plasma parameters in H-mode density limit on the JET-ILW

Abstract

ASJC Scopus subject areas

Keywords

Access to Document

Other files and links

Cite this