Transport Physics in Reversed Shear Plasmas

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Reversed magnetic shear is considered a good candidate for improving the tokamak concept because it has the potential to stabilize MHD instabilities and reduce particle and energy transport. With reduced transport the high pressure gradient would generate a strong off-axis bootstrap current and could sustain a hollow current density profile. Such a combination of favorable conditions could lead to an attractive steady-state tokamak configuration. Indeed, a new tokamak confinement regime with reversed magnetic shear has been observed on the Tokamak Fusion Test Reactor (TFTR) where the particle, momentum, and ion thermal diffusivities drop precipitously, by over an order of magnitude. ... continued below

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17 p.

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Levinton, F.M.; Batha, S.H.; Beer, M.A.; Bell, M.G.; Budny, R.V.; Efthimion, P.C. et al. December 31, 1997.

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Reversed magnetic shear is considered a good candidate for improving the tokamak concept because it has the potential to stabilize MHD instabilities and reduce particle and energy transport. With reduced transport the high pressure gradient would generate a strong off-axis bootstrap current and could sustain a hollow current density profile. Such a combination of favorable conditions could lead to an attractive steady-state tokamak configuration. Indeed, a new tokamak confinement regime with reversed magnetic shear has been observed on the Tokamak Fusion Test Reactor (TFTR) where the particle, momentum, and ion thermal diffusivities drop precipitously, by over an order of magnitude. The particle diffusivity drops to the neoclassical level and the ion thermal diffusivity drops to much less than the neoclassical value in the region with reversed shear. This enhanced reversed shear (ERS) confinement mode is characterized by an abrupt transition with a large rate of rise of the density in the reversed shear region during neutral beam injection, resulting in nearly a factor of three increase in the central density to 1.2 X 10(exp 20) cube m. At the same time the density fluctuation level in the reversed shear region dramatically decreases. The ion and electron temperatures, which are about 20 keV and 7 keV respectively, change little during the ERS mode. The transport and transition into and out of the ERS mode have been studied on TFTR with plasma currents in the range 0.9-2.2 MA, with a toroidal magnetic field of 2.7-4.6 T, and the radius of the q(r) minimum, q{sub min}, has been varied from r/a = 0.35 to 0.55. Toroidal field and co/counter neutral beam injection toroidal rotation variations have been used to elucidate the underlying physics of the transition mechanism and power threshold of the ERS mode.

Physical Description

17 p.

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OSTI as DE98000585

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  • 16. International Atomic Energy Agency (IAEA) fusion energy conference, Montreal (Canada), 7-11 Oct 1997; Other Information: DN: IAEA-CN--64/A1-3 Prepared in collaboration with Fusion Physics and Technology, Inc., Torrance, CA., and Princeton Univ., Princeton, NJ. [540 987654]

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  • Other: DE98000585
  • Report No.: ORNL/CP--94704
  • Report No.: CONF-9710100--
  • Grant Number: AC02-76CH03073
  • Office of Scientific & Technical Information Report Number: 625386
  • Archival Resource Key: ark:/67531/metadc689762

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  • December 31, 1997

Added to The UNT Digital Library

  • Aug. 14, 2015, 8:43 a.m.

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  • Jan. 21, 2016, 1:23 p.m.

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Levinton, F.M.; Batha, S.H.; Beer, M.A.; Bell, M.G.; Budny, R.V.; Efthimion, P.C. et al. Transport Physics in Reversed Shear Plasmas, article, December 31, 1997; Tennessee. (digital.library.unt.edu/ark:/67531/metadc689762/: accessed October 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.