How the birth and death of shear layers determine confinement evolution: from the L → H transition to the density limit

Diamond, Patrick H.; Singh, Rameswar; Long, Ting; Hong, Rongjie; Ke, Rui; Yan, Zheng; Cao, Mingyun; Tynan, George R.

doi:10.1098/rsta.2021.0227

Title: How the birth and death of shear layers determine confinement evolution: from the L → H transition to the density limit

Journal Article · Mon Jan 02 00:00:00 EST 2023 · Philosophical Transactions of the Royal Society. A, Mathematical, Physical and Engineering Sciences

DOI:https://doi.org/10.1098/rsta.2021.0227· OSTI ID:1907842

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Univ. of California San Diego, La Jolla, CA (United States)
Southwestern Institute of Physics, Chengdu (China)
Univ. of California, Los Angeles, CA (United States)
Univ. of Wisconsin, Madison, WI (United States)
Univ. of California, San Diego, CA (United States)

Electric field profile structure—especially its shear—is a natural order parameter for the edge plasma, and characterizes confinement regimes ranging from the H-mode (Wagner et al. 1982 Phys. Rev. Lett.49, 1408–1412 (doi:10.1103/PhysRevLett.49.1408)) to the density limit (DL) (Greenwald et al. 1988 Nucl. Fusion28, 2199–2207 (doi:10.1088/0029-5515/28/12/009)). The theoretical developments and lessons learned during 40 years of H-mode studies (Connor & Wilson 1999 Plasma Phys. Control. Fusion42, R1–R74 (doi:10.1088/0741-3335/42/1/201); Wagner 2007 Plasma Phys. Control. Fusion49, B1–B33 (doi:10.1088/0741-3335/49/12b/s01)) are applied to the shear layer collapse paradigm (Hong et al. 2017 Nucl. Fusion58, 016041 (doi:10.1088/1741-4326/aa9626)) for the onset of DL phenomena. Results from recent experiments on edge shear layers and DL phenomenology are summarized and discussed in the light of L → H transition physics. The theory of shear layer collapse is then developed. In this work, we demonstrate that shear layer physics captures both the well known current (Greenwald) scaling of the DL (Greenwald 2002 Plasma Phys. Control. Fusion44, R27–R53 (doi:10.1088/0741-3335/44/8/201); Greenwald et al. 2014 Phys. Plasmas21, 110501 (doi:10.1063/1.4901920)), as well as the emerging power scaling (Zanca, Sattin, JET Contributors 2019 Nucl. Fusion59, 126011 (doi:10.1088/1741-4326/ab3b31)). The derivation of the power scaling theory exploits an existing model, originally developed for the L → H transition (Diamond, Liang, Carreras, Terry 1994 Phys. Rev. Lett.72, 2565–2568 (doi:10.1103/PhysRevLett.72.2565); Kim & Diamond 2003 Phys. Rev. Lett.90, 185006 (doi:10.1103/PhysRevLett.90.185006)). We describe the enhanced particle transport events that occur following shear layer collapse. Open problems and future directions are discussed.

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Research Organization:: Univ. of California, San Diego, CA (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES); National Science Foundation (NSF); National Key Research and Development Program of China; National Natural Science Foundation of China (NSFC)

Grant/Contract Number:: FG02-04ER54738; FG02-07ER54912; AC02-09CH11466; SC0022528; NSF PHY-1748958; 2018YFE0310300; 2022YFE03100004; U1867222; 11905050; 11875124; 2022NSFSC1791; 2020JDTD0030

OSTI ID:: 1907842

Journal Information:: Philosophical Transactions of the Royal Society. A, Mathematical, Physical and Engineering Sciences, Vol. 381, Issue 2242; ISSN 1364-503X

Publisher:: The Royal Society PublishingCopyright Statement

Country of Publication:: United States

Language:: English

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Title: How the birth and death of shear layers determine confinement evolution: from the L → H transition to the density limit

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