Long wavelength turbulence as well as heat and momentum transport are signi
ficantly reduced in the DIII-D tokamak [Plasma Physics and Controlled Nucle
ar 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 incre
ases by up to 80%. Fully saturated turbulence measurements near rho = 0.7 (
rho = r/a) in the wave number range 0.1 less than or equal to k(perpendicul
ar to)rho(s) less than or equal to 0.6, obtained with beam emission spectro
scopy, exhibit a significant reduction of fluctuation power after neon inje
ction. 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. Gyrokineti
c linear stability simulations of these plasmas are qualitatively consisten
t, showing a reduction in the growth rate of ion temperature gradient drive
n modes for 0 < k(perpendicular to)rho(s) less than or equal to 1.4, and no
nlinear gyrokinetic simulations show a reduced saturated density fluctuatio
n amplitude. The measured omega(ExB) shearing rate increased at rho = 0.7,
suggesting that impurity-induced growth rate reduction is acting synergisti
cally with omega(ExB) shear to decrease turbulence and reduce anomalous tra
nsport. (C) 2000 American Institute of Physics. [S1070-664X(00)92805-2].