Investigation of the transient electromagnetic processes and forces in metallic environments of large superconducting magnets by an optimized finite element approach

The stellarator Wendelstein 7-X is a steady state fusion experiment being b uilt by the Max-Planck-Institute for Plasma Physics. The magnetic fields wh ich are needed to enclose the plasma are to be supplied by superconducting coils. The steel plasma vessel and a helium cooled heat radiation shield ar e located between the coil system and the plasma space. Eddy currents are i nduced in these metal structures during an emergency discharge of the magne t system, The calculation of their effects-force density and heating-is, du e to the complex geometry of the system, not possible neither with analytic al tools nor by a complete modeling with conventional methods. Therefore, t he new modeling method presented here, which is based on the FEM, was devel oped. In this method the spatial distribution of the magnetic vector potent ial A(r) is calculated. This calculation is done by a program based on the general Biot-Savart's law Afterwards the calculated vector potential is giv en, with the help of the method of the Lagrange Multipliers, in time varyin g form at every node, With the help of these calculations, suitable measure s can be taken to reduce the eddy currents and the resulting forces in the cooling shield.