Stability of negative central magnetic shear discharges in the DIII-D tokamak

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Discharges with negative central magnetic shear (NCS) hold the promise of enhanced fusion performance in advanced tokamaks. However, stability to long wavelength magnetohydrodynamic modes is needed to take advantage of the improved confinement found in NCS discharges. The stability limits seen in DIII-D experiments depend on the pressure and current density profiles and are in good agreement with stability calculations. Discharges with a strongly peaked pressure profile reach a disruptive limit at low beta, {beta}{sub N} = {beta} (I/aB){sup -1} {le} 2.5 (% m T/MA), caused by an n = 1 ideal internal kink mode or a global resistive instability ... continued below

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31 p.

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Strait, E.J.; Chu, M.S. & Ferron, J.R. December 1, 1996.

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  • General Atomic Company
    Publisher Info: General Atomics, San Diego, CA (United States)
    Place of Publication: San Diego, California

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Discharges with negative central magnetic shear (NCS) hold the promise of enhanced fusion performance in advanced tokamaks. However, stability to long wavelength magnetohydrodynamic modes is needed to take advantage of the improved confinement found in NCS discharges. The stability limits seen in DIII-D experiments depend on the pressure and current density profiles and are in good agreement with stability calculations. Discharges with a strongly peaked pressure profile reach a disruptive limit at low beta, {beta}{sub N} = {beta} (I/aB){sup -1} {le} 2.5 (% m T/MA), caused by an n = 1 ideal internal kink mode or a global resistive instability close to the ideal stability limit. Discharges with a broad pressure profile reach a soft beta limit at significantly higher beta, {beta}{sub N} = 4 to 5, usually caused by instabilities with n > 1 and usually driven near the edge of the plasma. With broad pressure profiles, the experimental stability limit is independent of the magnitude of negative shear but improves with the internal inductance, corresponding to lower current density near the edge of the plasma. Understanding of the stability limits in NCS discharges has led to record DIII-D fusion performance in discharges with a broad pressure profile and low edge current density.

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31 p.

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INIS; OSTI as DE97003366

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  • Meeting of the Division of Plasma Physics of the American Physical Society, Denver, CO (United States), 11-15 Nov 1996

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  • Other: DE97003366
  • Report No.: GA-A--22522
  • Report No.: CONF-961102--5
  • Grant Number: AC03-89ER51114
  • Office of Scientific & Technical Information Report Number: 451201
  • Archival Resource Key: ark:/67531/metadc674798

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Office of Scientific & Technical Information Technical Reports

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  • December 1, 1996

Added to The UNT Digital Library

  • July 25, 2015, 2:21 a.m.

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  • April 18, 2016, 5:49 p.m.

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Strait, E.J.; Chu, M.S. & Ferron, J.R. Stability of negative central magnetic shear discharges in the DIII-D tokamak, article, December 1, 1996; San Diego, California. (digital.library.unt.edu/ark:/67531/metadc674798/: accessed October 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.