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- Mikkelsen, D.R, et al.
(författare)
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Assessment of Transport in NCSX
- 2007
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Ingår i: Fusion Science and Technology. ; 51, s. 166-180
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Tidskriftsartikel (refereegranskat)abstract
- We explore whether the energy confinement and planned heating in the National Compact Stellarator Experiment (NCSX) are sufficient to test magnetohydrodynamic (MHD) stability limits, and whether the configuration is sufficiently quasi-axisymmetric to reduce the neoclassical ripple transport to low levels, thereby allowing tokamak-like transport. A zero-dimensional model with fixed profile shapes is related to global energy confinement scalings for stellarators and tokamaks, neoclassical transport properties are assessed with the DKES, NEO, and NCLASS codes, and a power balance code is used to predict temperature profiles. Reaching the NCSX goal of = 4% at low collisionality will require HISS-95 = 3, which is higher than the best achieved in present stellarators. However, this level of confinement is actually ~10% lower than that predicted by the ITER-97P tokamak L-mode scaling. By operating near the stellarator density limit, the required HISS-95 is reduced by 35%. The high degree of quasi-axisymmetry of the configuration and the self-consistent "ambipolar" electric field reduce the neoclassical ripple transport to a small fraction of the neoclassical axisymmetric transport. A combination of neoclassical and anomalous transport models produces pressure profile shapes that are within the range of those used to study the MHD stability of NCSX. We find that = 4% plasmas are "neoclassically accessible" and are compatible with large levels of anomalous transport in the plasma periphery.
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