Quasilinear Carbon Transport In An Impurity Hole Plasma In LHD
Authors: D.R. Mikkelsen, K. Tanaka, M. Nunami, T.-H. Watanabe, H. Sugama, M. Yoshinuma, K. Ida, Y. Suzuki, M. Goto, S. Morita, B. Wieland, I. Yamada, R. Yasuhara, T. Tokuzawa, T. Akiyama and N.A. Pablant
Abstract: Comprehensive electrostatic gyrokinetic linear stability calculations for
ion-scale microinstabilities
in an LHD plasma with an ion-ITB and carbon "impurity hole" are
used to make quasilinear estimates of particle flux to explore whether microturbulence
can explain the observed outward carbon fluxes that flow "up" the impurity
density gradient. The ion temperature is not stationary in the ion-ITB phase of the
simulated discharge, during which the core carbon density decreases continuously. To
fully sample these varying conditions the calculations are carried out at three radial
locations and four times. The plasma parameter inputs are based on experimentally
measured profiles of electron and ion temperature, as well as electron and carbon
density. The spectroscopic line-average ratio of hydrogen and helium densities is
used to set the density of these species. Three ion species (H,He,C) and the electrons
are treated kinetically, including collisions. Electron instability drive does enhance
the growth rate significantly, but the most unstable modes have characteristics of
ion temperature gradient (ITG) modes in all cases. As the carbon density gradient
is scanned between the measured value and zero, the quasilinear carbon flux is
invariably inward when the carbon density profile is hollow, so turbulent transport
due to the instabilities considered here does not explain the observed outward flux
of impurities in impurity hole plasmas. The stiffness of the quasilinear ion heat flux
is found to be 1.7-2.3, which is lower than several estimates in tokamaks.
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Published in: Phys. Plasmas 21 , 082302 (2014) ; http://dx.doi.org/10.1063/1.4890973
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