Authors: R.M. Churchill, C.S. Chang,
R. Hager, R. Maingi, R. Nazikian, D.P. Stotler
Abstract: Scrape-off layer (SOL) physics in tokamak
devices are typically simulated using fluid codes, due to the
generally high collisionality in this region. However,
research has revealed a number of discrepancies between experiment
and leading SOL fluid codes (e.g. SOLPS), including
underestimating outer target temperatures[1], radial electric
field in the SOL[2, 3, 1], parallel ion SOL flows at the low field
side[4, 3, 5], and impurity radiation[6]. It was
hypothesized by Chankin et al.[3] that these discrepancies
stem from the ad-hoc treatment of kinetic effects in fluid codes."
"To determine the importance of
kinetic effects in the SOL, simulations
were undertaken using the XGCa code[7], a total-f , gyrokinetic
code which self- consistently calculates the axisymmetric
electrostatic potential and plasma dynamics, and includes modules
for Monte Carlo neutral transport. General features of the
simulation results are investigated for kinetic effects, but
also in the future comparisons will be made to the fluid SOL
transport code SOLPS[8]. We note here that the present study
is without turbulence. Turbulence may alter the
results presented here. Here we focus on the question of
parallel pressure balance in a low-density, low-power DIII-D
H-mode plasma. A significant deviation from standard total
pressure balance (pe + pi + mi ni
Vi 2= const) occurs in
the SOL of these XGCa simulations, and
here we explore whether the addition of main ion
viscosity and neutral source terms can account for this
deviation. The rest of the
paper is organized as follows:
Section 2 briefly describes the
XGCa code, Section 3 details
some of the simulation
setup, Section 4 discusses details of the pressure
balance parallel to magnetic field lines, including main ion
viscosity and neutral source terms, and Section 5
wraps up with conclusions and plans for future
work.
Submitted to: Nuclear Fusion
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