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Author(s):
M.Okamoto and N.Nakajima
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Title:
Bootstrap Currents in Stellarators and Tokamaks
Date of publication:
Sep. 1990
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Key words:
bootstrap current, Ohkawa current, neoclassical theory, stellarator, parallel viscosity, 1/nu regime, ripple diffusion, Large Helical Device.
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Abstract:
The remarkable feature of the bootstrap current in stellarators is it's strong dependence on the magnetic field configuration. Neoclassical bootstrap currents in a large helical device of torsatron/heliotron type (L = 2, M = 10, R = 4 m, B = 4 T) is evaluated in the banana ( 1/nu ) and the plateau regime. Various vacuum magnetic field configurations are studied with a view to minimizing the bootstrap current. It is found that in the banana regime, shifting of the magnetic axis and shaping of magnetic surfaces have a remarkable influence on the bootstrap current ; a small outward shift of the magnetic axis and vertically elongated magnetic surfaces are favourable for a reduction of the bootstrap current. It is noted, however, that the ripple diffusion in the 1/nu regime has opposite tendency to the bootstrap current ; it increases with the outward shift and increases as the plasma cross section is vertically elongated. The comparison will be made between bootstrap currents in stellarators and tokamaks.
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