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This content will become publicly available on March 28, 2019

Title: Relationship between locked modes and thermal quenches in DIII-D

Locked modes are known to be one of the major causes of disruptions, but the physical mechanisms by which locking leads to disruptions are not well understood. For this study, we analyze the evolution of the temperature profile in the presence of multiple coexisting locked modes during partial and full thermal quenches. Partial quenches are often observed to be an initial, distinct stage in the full thermal quench. Near the onset of partial quenches, locked island O-points are observed to align with each other on the midplane, and their widths are sufficient to overlap each other, as indicated by the Chirikov parameter. Energy conservation analysis of one partial thermal quench shows that the energy lost is both radiated in the divertor region, and conducted or convected to the divertor. Nonlinear resistive magnetohydrodynamic simulations support the interpretation of stochastic fields causing a partial axisymmetric collapse, though the simulated temperature profile exhibits less degradation than the experimental profiles. In discharges with minimum values of the safety factor above ~1.2, locked modes are observed to self-stabilize by inducing, possibly via double tearing modes, a minor disruption that removes their neoclassical drive. These high q min discharges often exhibit relatively low ratios of themore » plasma internal inductance to the safety factor at 95% of the poloidal flux, which might imply classical stability, in agreement with the decay of the mode when the neoclassical drive is removed.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [5] ;  [6] ; ORCiD logo [6] ;  [6] ; ORCiD logo [2]
  1. Columbia Univ., New York, NY (United States); ITER Organization, St. Paul Lez Durance (France)
  2. Columbia Univ., New York, NY (United States)
  3. Univ. of Texas, Austin, TX (United States)
  4. Univ. of California, San Diego, CA (United States). Center for Energy Research
  5. Ludwig Maximilian Univ., Munich (Germany)
  6. General Atomics, San Diego, CA (United States)
Publication Date:
Grant/Contract Number:
FC02-04ER54698; SC0008520; SC0016372; FG02-97ER54415; FG02-04ER54761; FG02-92ER54139
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 58; Journal Issue: 5; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
U.S. Dept. of Energy
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Contributing Orgs:
The DIII-D Team
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
OSTI Identifier:
1432050