Core turbulence and transport reduction in DIII-D discharges with weak or negative magnetic shear

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Core turbulence fluctuation levels have been suppressed in DIII-D discharges with weak or negative magnetic shear (NCS) near the magnetic axis. In some weak magnetic shear discharges the ion thermal transport has been reduced to neoclassical levels throughout the whole plasma. The cause of the transport reduction is investigated by calculating the stability of toroidal drift waves, i.e., ion temperature gradient modes (ITG) and trapped electron modes (TE), with a comprehensive gyrokinetic linear stability code. It is found that the ITG modes and TE modes are stabilized by ExB velocity shear. The ExB velocity shear is primarily responsible for the ... continued below

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7 p.

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Staebler, G.M.; Greenfield, C.M. & Schissel, D.P. June 1, 1997.

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Core turbulence fluctuation levels have been suppressed in DIII-D discharges with weak or negative magnetic shear (NCS) near the magnetic axis. In some weak magnetic shear discharges the ion thermal transport has been reduced to neoclassical levels throughout the whole plasma. The cause of the transport reduction is investigated by calculating the stability of toroidal drift waves, i.e., ion temperature gradient modes (ITG) and trapped electron modes (TE), with a comprehensive gyrokinetic linear stability code. It is found that the ITG modes and TE modes are stabilized by ExB velocity shear. The ExB velocity shear is primarily responsible for the spontaneous growth of a region of suppressed ion thermal transport. Surprisingly, the negative magnetic shear and Shafranov shift are only weak stabilizing influences for the ITG and TE modes in the DIII-D cases studied. Negative magnetic shear does eliminate the ideal magnetohydrodynamic ballooning mode instability which is a necessary access criteria for these improved core confinement regimes. Dilution of the thermal ions by fast ions from the heating beams and hot ions compared to electrons are found to be important stabilizing influences in the core.

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7 p.

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INIS; OSTI as DE97007377

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  • 24. EPS conference on controlled fusion and plasma physics, Berchtesgaden (Germany), 9-13 Jun 1997

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  • Other: DE97007377
  • Report No.: GA-A--22617
  • Report No.: CONF-9706131--2
  • Grant Number: AC03-89ER51114;AC05-96OR22464;FG05-88ER53266;FG02-92ER54139;FG02-89ER53297;W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 505398
  • Archival Resource Key: ark:/67531/metadc699294

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • June 1, 1997

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  • Aug. 14, 2015, 8:43 a.m.

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  • Aug. 1, 2016, 6:34 p.m.

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Staebler, G.M.; Greenfield, C.M. & Schissel, D.P. Core turbulence and transport reduction in DIII-D discharges with weak or negative magnetic shear, article, June 1, 1997; San Diego, California. (digital.library.unt.edu/ark:/67531/metadc699294/: accessed October 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.