Speaker
Weixing Wang
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.J604.pdf
Turbulence
W. X. Wang1 , E. Startsev1 , S. Ethier1 , J. Chen1 , C. H. Ma1 , T. S. Hahm2 , M. G. Yoo2
1 Princeton Plasma Physics Laboratory, Princeton, USA
2 Seoul National University, Seoul, Korea
Plasma self-generated current (e.g., the bootstrap current) contributes to the generation of
poloidal magnetic field for plasma confinement in tokamaks, and also strongly affects key MHD
instabilities. It is found that plasma turbulence may strongly influence self-driven current gen-
eration. This could have a radical impact on various aspects of tokamak physics. Our simulation
study employs a global gyrokinetic model coupling self-consistent neoclassical and turbulent
dynamics with focus on mean electron current. Distinct phases in electron current generation
are illustrated in our initial value simulation. In the early phase before turbulence develops,
the electron bootstrap current is established in a time scale of a few electron collision times,
which closely agrees with the neoclassical prediction. The second phase follows when turbu-
lence begins to saturate, during which turbulent fluctuations are found to strongly affect electron
current. The profile structure, amplitude and phase space structures of electron current density
are all significantly modified relative to the neoclassical bootstrap current by the presence of
turbulence. Both electron parallel acceleration and parallel residual stress drive due to turbu-
lence are shown to play important roles in turbulence-induced current generation. The former
can change the total plasma self-generated current though turbulence-induced momentum ex-
change between electrons and ions, and the latter merely modifies the current density profile
while keeping the total current unchanged. The current density profile is modified in a way that
correlates with the fluctuation intensity gradient through its effect on k -symmetry breaking in
fluctuation spectrum. Turbulence is shown to reduce (enhance) plasma self-generated current
in low (high) collisionality regime, and the reduction of total electron current relative to the
neoclassical bootstrap current increases as collisionality decreases. The implication of this re-
sult to the fully non-inductive current operation in steady state burning plasma regime could be
important and should be investigated. Finally, a significant non-inductive current is observed in
flat pressure region, which is a nonlocal effect and results from turbulence-spreading-induced
current diffusion. Work supported by U.S. DOE Contract DE-AC02-09-CH11466.
