Increased nonlinear coupling between turbulence and low-frequency fluctuations at the L-H transition.
The nonlinear coupling between small scale high-frequency turbulence and larger scale lower-frequency fluctuations increases transiently in transitions to improved confinement in the DIII-D tokamak. This increase starts before the rapid turbulence suppression and E x B shear-flow development in the region that becomes the H-mode transport barrier/shear flow region. After the transition, the coupling returns to L-mode levels. These results are consistent with expectations for spontaneous transitions to improved confinement triggered by a turbulence-driven sheared flow.
Moyer
R A
RA
Mechanical and Aerospace Engineering Department, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA.
Tynan
G R
GR
Holland
C
C
Burin
M J
MJ