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Author(s):
K. Nagasaki and K. Itoh
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Title:
Magnetic Field Structure near the Plasma Boundary in Helical Systems and Divertor Tokamaks
Date of publication:
Feb. 1990
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Key words:
edge magnetic field, divertor tokamak, toroidal helical system, magnetic braiding, connection length to the wall
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Abstract:
Magnetic field structure of the scrape off layer (SOL) region in both helical systems and divertor tokamaks is studied numerically by using model fields. The connection length of the field line to the wall is calculated. In helical systems, the connection length, L, has a logarithmic dependence on the distance from the outermost magnetic surface or that from the residual magnetic islands. The effect of axisymmetric fields on the field structure is also determined. In divertor tokamaks, the connection length also has logarithmic properties near the separatrix. Even when the perturbations, which resonate to rational surfaces near the plasma boundary, are added, Iogarithmic properties still remain. We compare the connection length of torsatron/helical-heliotron systems with that of divertor tokamaks. It is found that the former is shorter than the latter by one order magnitude with similar aspect ratio.
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