Impurity-induced turbulence suppression and reduced transport in the DIII-D tokamak
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)
Long wavelength turbulence as well as heat and momentum transport are significantly reduced in the DIII-D tokamak [Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] as a result of neon seeding of a low confinement mode negative central shear discharge. Correspondingly, the energy confinement time increases by up to 80%. Fully saturated turbulence measurements near {rho}=0.7 ({rho}=r/a) in the wave number range 0.1{<=}k{sub (perpendicular} {sub sign)}{rho}{sub s}{<=}0.6, obtained with beam emission spectroscopy, exhibit a significant reduction of fluctuation power after neon injection. Fluctuation measurements obtained with far infrared scattering also show a reduction of turbulence in the core, while the Langmuir probe array measures reduced particle flux in the edge and scrape-off layer. Gyrokinetic linear stability simulations of these plasmas are qualitatively consistent, showing a reduction in the growth rate of ion temperature gradient driven modes for 0<k{sub (perpendicular} {sub sign)}{rho}{sub s}{<=}1.4, and nonlinear gyrokinetic simulations show a reduced saturated density fluctuation amplitude. The measured {omega}{sub ExB} shearing rate increased at {rho}=0.7, suggesting that impurity-induced growth rate reduction is acting synergistically with {omega}{sub ExB} shear to decrease turbulence and reduce anomalous transport. (c) 2000 American Institute of Physics.
- OSTI ID:
- 20216055
- Journal Information:
- Physics of Plasmas, Vol. 7, Issue 5; Other Information: PBD: May 2000; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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