Rotation and neoclassical ripple transport in ITER

E. J. Paul, M. Landreman, F. M. Poli, D. A. Spong, H. M. Smith, W. Dorland

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

Neoclassical transport in the presence of non-axisymmetric magnetic fields causes a toroidal torque known as neoclassical toroidal viscosity (NTV). The toroidal symmetry of ITER will be broken by the finite number of toroidal field coils and by test blanket modules (TBMs). The addition of ferritic inserts (FIs) will decrease the magnitude of the toroidal field ripple. 3D magnetic equilibria in the presence of toroidal field ripple and ferromagnetic structures are calculated for an ITER steady-state scenario using the variational moments equilibrium code (VMEC). Neoclassical transport quantities in the presence of these error fields are calculated using the stellarator Fokker-Planck iterative neoclassical conservative solver (SFINCS). These calculations fully account for E r, flux surface shaping, multiple species, magnitude of ripple, and collisionality rather than applying approximate analytic NTV formulae. As NTV is a complicated nonlinear function of E r, we study its behavior over a plausible range of E r. We estimate the toroidal flow, and hence E r, using a semi-analytic turbulent intrinsic rotation model and NUBEAM calculations of neutral beam torque. The NTV from the ripple dominates that from lower n perturbations of the TBMs. With the inclusion of FIs, the magnitude of NTV torque is reduced by about 75% near the edge. We present comparisons of several models of tangential magnetic drifts, finding appreciable differences only for superbanana-plateau transport at small E r. We find the scaling of calculated NTV torque with ripple magnitude to indicate that ripple-trapping may be a significant mechanism for NTV in ITER. The computed NTV torque without ferritic components is comparable in magnitude to the NBI and intrinsic turbulent torques and will likely damp rotation, but the NTV torque is significantly reduced by the planned ferritic inserts.

Original languageEnglish
Article number116044
JournalNuclear Fusion
Volume57
Issue number11
DOIs
StatePublished - Aug 18 2017

Funding

The authors would like to thank I. Calvo, F. Parra, J. Hillesheim, J. Lee, G. Papp, S. Satake, and J. Harris for helpful input and discussions. This work was supported by the US Department of Energy through grants DE­FG02-93ER­54197 and DE­FC02­08ER­54964. The computations presented in this paper have used resources at the National Energy Research Scientific Computing Center (NERSC).

Keywords

  • 3D equilibrium
  • neoclassical toroidal viscosity
  • tokamak

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