外部ヘリカル磁場によるエルゴディック磁気リミタの形成

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Ergodic magnetic limiter has been conceived as a concept of impurity control for an advanced tokamak. The structure of magnetic field line in the so-called ergodic layer is quite important for the particle and heat transport there. In this note ergodization of magnetic field line is studied in terms of island overlapping for both local and nonlocal helical windings using a field line tracing computer code.<BR>A helical winding of mode index m/n, m and n are poloidal and toroidal mode numbers, on the torus chamber generates a number of sidebands in addition to the main helical mode m/n through the generation of higher harmonics from filamentary coil current and the toroidicity. The contribution from the latter was analyzed by Morozov and Solov'ev and has been considered small and neglected. However is our finding that the sideband generation by toroidicity from pure helical field on the cylinder is comparable to the higher harmonics generation from filamentary coil.<BR>It has been thought that the ergodization comes from the island overlapping of the main and the first sideband modes. We found, however, that the island overlapping of higher sideband modes is the origin of ergodization if we have the higher order rational surfaces in the exterior to the first sideband resonance layer and that the helical field is weak.<BR>Finally we note that an ergodized layer does not extend close to the chamber wall when the helical coils are wound on the chamber wall. Therefore the heat and particle flux is not uniform on the wall but localized. In order to improve heat load pattern on the wall and particle removal, we propose the scheme of rotating ergodic layer associated with a pump limiter.
社団法人プラズマ・核融合学会の論文

外部ヘリカル磁場によるエルゴディック磁気リミタの形成

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