Nonlocal Neoclassical Transport in Tokamak and Spherical Torus Experiments
Authors: W.X. Wang, G. Rewoldt, W.M. Tang, F.L. Hinton, J. Manickam, L.E. Zakharov, R.B. White, and S. Kaye
Abstract:
Nonlocal neoclassical effects of large ion orbits on ion heat transport, the ambipolar radial electric field and the bootstrap current in realistic toroidal plasmas are investigated using a global δf particle simulation. It is found that the conventional local, linear gradient-flux relation is broken for the ion thermal transport near the magnetic axis. With regard to the transport level, it can be either lower or higher than the prediction of standard neoclassical theory, depending on the details of the ion temperature profile. Particularly, this non-local feature is suggested to exist in NSTX plasmas, being consistent with NSTX experimental evidence. It is also shown that a large ion temperature gradient can increase the bootstrap current, but a steep density gradient has little effect. When the plasma rotation is taken into account, the rotation gradient can drive an additional parallel flow for the ions and then additional bootstrap current, either positive or negative, depending on the gradient direction. Compared with the radial force balance estimate, our non-local simulation predicts a significantly deeper radial electric field well at the location of an internal transport barrier of an NSTX discharge.
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Physics of Plasmas 13, 082501 (2006) 15 pp
doi: 10.1063/1.2244532
© (2006) American Institute of Physics.
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