Stability of DIII-D high-performance, negative central shear discharges

Hanson, Jeremy M.; Berkery, John W.; Bialek, James M.; Clement, Mitchell; Ferron, John R.; Garafalo, Andrea M.; Holcomb, Christopher T.; La Haye, Robert J.; Lanctot, Matthew J.; Luce, Timothy C.; Navratil, Gerald A.; Olofsson, K. Erik J.; Strait, Edward J.; Turco, Francesca; Turnbull, Alan D.

doi:10.1088/1741-4326/aa6266

Title: Stability of DIII-D high-performance, negative central shear discharges

Journal Article · Mon Mar 20 00:00:00 EDT 2017 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/aa6266· OSTI ID:1354791

Hanson, Jeremy M. ^[1]; Berkery, John W. ^[1]; Bialek, James M. ^[1]; Clement, Mitchell ^[2]; Ferron, John R. ^[3]; Garafalo, Andrea M. ^[3]; Holcomb, Christopher T. ^[4]; La Haye, Robert J. ^[3]; Lanctot, Matthew J. ^[3]; Luce, Timothy C. ^[3]; Navratil, Gerald A. ^[1]; Olofsson, K. Erik J. ^[5]; Strait, Edward J. ^[3]; Turco, Francesca ^[1]; Turnbull, Alan D. ^[3]

Columbia Univ., New York, NY (United States)
Columbia Univ., New York, NY (United States); Univ. of California San Diego, La Jolla, CA (United States)
General Atomics, San Diego, CA (United States)
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
ORAU Oak Ridge Associated Univ., Oak Ridge, TN (United States)

Tokamak plasma experiments on the DIII-D device demonstrate high-performance, negative central shear (NCS) equilibria with enhanced stability when the minimum safety factor q_min exceeds 2, qualitatively confirming theoretical predictions of favorable stability in the NCS regime. The discharges exhibit good confinement with an L-mode enhancement factor H₈₉ = 2.5, and are ultimately limited by the ideal-wall external kink stability boundary as predicted by ideal MHD theory, as long as tearing mode (TM) locking events, resistive wall modes (RWMs), and internal kink modes are properly avoided or controlled. Although the discharges exhibit rotating TMs, locking events are avoided as long as a threshold minimum safety factor value q_min > 2 is maintained. Fast timescale magnetic feedback control ameliorates RWM activity, expanding the stable operating space and allowing access to β_N values approaching the ideal-wall limit. Quickly growing and rotating instabilities consistent with internal kink mode dynamics are encountered when the ideal-wall limit is reached. The RWM events largely occur between the no- and ideal-wall pressure limits predicted by ideal MHD. However, evaluating kinetic contributions to the RWM dispersion relation results in a prediction of passive stability in this regime due to high plasma rotation. In addition, the ideal MHD stability analysis predicts that the ideal-wall limit can be further increased to β_N > 4 by broadening the current profile. Furthermore, this path toward improved stability has the potential advantage of being compatible with the bootstrap-dominated equilibria envisioned for advanced tokamak (AT) fusion reactors.

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Research Organization:: General Atomics, San Diego, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Organization:: USDOE Office of Nuclear Energy (NE)

Grant/Contract Number:: FC02-04ER54698; AC52-07NA27344

OSTI ID:: 1354791

Alternate ID(s):: OSTI ID: 1838263

Report Number(s):: LLNL-JRNL-830402

Journal Information:: Nuclear Fusion, Vol. 57, Issue 5; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 7 works

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