Calculation of Neoclassical Toroidal Viscosity with a Particle Simulation in the Tokamak Magnetic Breaking Experiments
Authors: Kimin Kim, et. al.
Abstract:
Accurate calculation of perturbed distribution function δf and perturbed
magnetic fi eld δB is essential to achieve prediction of non-ambipolar transport and
neoclassical toroidal viscosity (NTV) in perturbed tokamaks. This paper reports a
study of the NTV with a δf particle code (POCA) and improved understanding of
magnetic braking in tokamak experiments. POCA calculates the NTV by computing
f with guiding-center orbit motion and using B from the ideal perturbed equilibrium
code (IPEC). POCA simulations are compared with experimental estimations for
NTV, which are measured from angular momentum balance (DIII-D) and toroidal
rotational damping rate (NSTX). The calculation shows good agreement in total NTV
torque for the DIII-D discharge, where an analytic neoclassical theory also gives a
consistent result thanks to relatively large aspect-ratio and slow toroidal rotations. In
NSTX discharges, where the aspect-ratio is small and the rotation is fast, the theory
only gives a qualitative guide for predicting NTV. However, the POCA simulation
largely improves the quantitative NTV prediction for NSTX. It is discussed that a self-
consistent calculation of δB using general perturbed equilibria is eventually necessary
since a non-ideal plasma response can change the perturbed eld and thereby the NTV
torque.
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Submitted to: Nuclear Fusion (January 2013)
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Download PPPL-4869 (pdf 1.45 MB 16 pp)
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