A series of three otherwise identical DIII-D [J. L. Luxon, F. Batty, C. B.
Baxi , Plasma Physics and Controlled Nuclear Fusion Research 1986 (Internat
ional Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] L-mode (low conf
inement mode) plasma experiments with and without neon injection was analyz
ed with neoclassical theory. The measured increases in momentum and energy
confinement times, central rotation speed, and ExB with increasing neon inj
ection are predicted quantitatively by neoclassical theory, in particular b
y the predicted increase in the inward neoclassical convective momentum and
energy fluxes with neon injection. This agreement between theory and exper
iment suggests that the physical mechanism by means of which neon injection
improves the confinement of these L-mode DIII-D plasmas is to increase the
inward neoclassical particle flux, and hence increase the inward convectiv
e momentum and energy fluxes. (C) 2001 American Institute of Physics.