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Title: Stabilization and prevention of the 2/1 neoclassical tearing mode for improved performance in DIII-D

Authors:
; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1170895
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nuclear Fusion; Journal Volume: 47; Journal Issue: 5
Country of Publication:
United States
Language:
English

Citation Formats

R,Prater, R.J. La,Haye, T.C,Luce, C.C,Petty, E.J,Strait, J.R,Ferron, D.A,Humphreys, A,Isayama, J,Lohr, K,Nagasaki, P.A,Politzer, M.R,Wade, and A.S,Welander. Stabilization and prevention of the 2/1 neoclassical tearing mode for improved performance in DIII-D. United States: N. p., 2007. Web. doi:10.1088/0029-5515/47/5/001.
R,Prater, R.J. La,Haye, T.C,Luce, C.C,Petty, E.J,Strait, J.R,Ferron, D.A,Humphreys, A,Isayama, J,Lohr, K,Nagasaki, P.A,Politzer, M.R,Wade, & A.S,Welander. Stabilization and prevention of the 2/1 neoclassical tearing mode for improved performance in DIII-D. United States. doi:10.1088/0029-5515/47/5/001.
R,Prater, R.J. La,Haye, T.C,Luce, C.C,Petty, E.J,Strait, J.R,Ferron, D.A,Humphreys, A,Isayama, J,Lohr, K,Nagasaki, P.A,Politzer, M.R,Wade, and A.S,Welander. Tue . "Stabilization and prevention of the 2/1 neoclassical tearing mode for improved performance in DIII-D". United States. doi:10.1088/0029-5515/47/5/001.
@article{osti_1170895,
title = {Stabilization and prevention of the 2/1 neoclassical tearing mode for improved performance in DIII-D},
author = {R,Prater and R.J. La,Haye and T.C,Luce and C.C,Petty and E.J,Strait and J.R,Ferron and D.A,Humphreys and A,Isayama and J,Lohr and K,Nagasaki and P.A,Politzer and M.R,Wade and A.S,Welander},
abstractNote = {},
doi = {10.1088/0029-5515/47/5/001},
journal = {Nuclear Fusion},
number = 5,
volume = 47,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}
  • Utilizing a capability to vary neutral beam torque injection in the DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] tokamak, m/n=2/1 neoclassical tearing mode onset thresholds are found to fall by about one unit in {beta}{sub N}, from {approx}3 to {approx}2, in ITER-like sawtoothing high-energy confinement modes of plasma operation [R. Aymar, Plasma Phys. Control. Fusion 42, B385 (2000)] as 'co-injected' torque and rotation are reduced. However, increasing levels of torque and rotation in the counter-direction do not lead to corresponding rises in {beta}{sub N} thresholds. More encouragingly, error field sensitivity is not found to increase in low rotationmore » plasmas, as might be expected theoretically. These results pose an interesting physics problem, as well as raising concern for future devices such as ITER. Further analyses have explored possible physics origins of the behavior. They suggest many of the usual effects expected to lead to a rotation dependence (mode coupling, wall drag, ion polarization currents) are not significant, with instead models that depend on the size and sign of rotation shear playing a role. Onset behavior suggests the mode is close to being intrinsically (classically) unstable when it appears, and a conceptual explanation is offered for a mechanism by which rotation shear feeds into the onset process through changes to the classical tearing stability index, {delta}{sup '}. Further parameter extensions and studies are desirable to fully resolve the underlying physics of this interesting process.« less
  • Neoclassical tearing modes (NTMs) often lead to the decrease of plasma performance and can lead to disruptions, which makes them a major impediment in the development of operating scenarios in present toroidal fusion devices. Recent gyrokinetic simulations predict a decrease of plasma turbulence and cross-field transport at the O-point of the islands, which in turn affects the NTM dynamics. In this paper, a heat transport model of magnetic islands employing spatially non-uniform cross-field thermal diffusivity (χ{sub ⊥}) is presented. This model is used to derive χ{sub ⊥} at the O-point from electron temperature data measured across 2/1 NTM islands inmore » DIII-D. It was found that χ{sub ⊥} at the O-point is 1 to 2 orders of magnitude smaller than the background plasma transport, in qualitative agreement with gyrokinetic predictions. As the anomalously large values of χ{sub ⊥} are often attributed to turbulence driven transport, the reduction of the O-point χ{sub ⊥} is consistent with turbulence reduction found in recent experiments. Finally, the implication of reduced χ{sub ⊥} at the O-point on NTM dynamics was investigated using the modified Rutherford equation that predicts a significant effect of reduced χ{sub ⊥} at the O-point on NTM saturation.« less
  • Neoclassical Tearing Modes (NTMs) often lead to the decrease of plasma performance and can lead to disruptions, which makes them a major impediment in the development of operating scenarios in present toroidal fusion devices. Recent gyrokinetic simulations predict a decrease of plasma turbulence and cross- eld transport at the O-point of the islands, which in turn affects the NTM dynamics. In this paper a heat transport model of magnetic islands employing spatially non-uniform cross-field thermal diffusivity (χ more » $$\perp$$) is presented. This model is used to derive χ $$\perp$$ at the O-point from electron temperature data measured across 2/1 NTM islands in DIII-D. It was found that χ $$\perp$$ at the O-point is 1 to 2 orders of magnitude smaller than the background plasma transport, in qualitative agreement with gyrokinetic predictions. As the anomalously large values of χ $$\perp$$ are often attributed to turbulence driven transport, the reduction of the O-point χ $$\perp$$ is consistent with turbulence reduction found in recent experiments. Lastly, the implication of reduced χ $$\perp$$ at the O-point on NTM dynamics was investigated using the modi ed Rutherford equation that predicts a significant effect of reduced χ $$\perp$$ at the O-point on NTM saturation.« less