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The effect of ferritic structural material on the magnetic field of stellarators

Authors
  • Harmeyer, E.
  • Kisslinger, J.
  • Wobig, H.
  • Max-Planck-Institut fuer Plasmaphysik, G...
Publication Date
Jan 01, 1999
Source
OpenGrey Repository
Keywords
Language
English
License
Unknown

Abstract

In a fusion reactor ferritic steel is strongly favoured as structural material, since the low activation after neutron irradiation makes it a very attractive candidate to mitigate the issue fo radioactive waste disposal. On the other side ferromagnetic material modifies the magnetic field of the current carrying coils and may have negative effects on the plasma confinement. Especially in stellarators any deviation from symmetry may lead to island formation and destruction of magnetic surfaces. In the following paper the general equations governing the magnetic field in stellarators with ferritic structural material are analysed and the basic effects are investigated in simple straight geometry where analytic solutions are available. A code has been established which allows one to compute the modified field in toroidal geometry. Since the ferritic material is saturated under reactor conditions, the effective permeability is in the range of 1.2 to 1.5. This leads to a small reduction of the rotational transform under normal conditions in which the symmetry of the field generated by the coils is not violated. Symmetry breaking error fields arise if the properties of the ferritic matter differ from period to period. This case has been simulated by the assumption of inhomogeneous magnetization in the 5 blanket modules. It is found that the islands in the boundary region, which in a Helias reactor are utilized for divertor actions can be strongly modified by these error fields, thus care must be taken to avoid geometrical and material asymmetries of a Helias reactor. (orig.) / SIGLE / Available from TIB Hannover: RA 71(III/241) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische Informationsbibliothek / DE / Germany

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