ITER design features serving for suppression of eddy- and halo related electromagnetic loads

Highlights: • One of main challenges in tokamaks is to suppress EM loads created in in-vessel parts. • This article explains examples on how such suppression was achieved by design means. • Described principles helped suppress loads in several folds, up to an order magnitude. • Described principles do open a path to robust design of various in-vessel parts in ITER. • Being quite generic, these principles may be used in various industrial applications. - Abstract: As any tokamak, ITER will operate with rather high magnetic fields. Quasi-static toroidal field inside of the vacuum vessel reaches ∼9 T and slow transient poloidal field ∼2.5 T. In a case of plasma vertical drift and disruption, characteristic times of magnetic fields variation are short: 1–2 ms at thermal quench phase and 10–300 ms at current quench phase, thus magnetic field derivative reaches 50–150 T/s. These fast transients induce intensive currents and ElectroMagnetic (EM) loads in conductive structures. EM loads at in-vessel components typically exceed gravity and seismic loads by two orders of magnitude. Induced currents are split in two groups: eddy currents closed completely in conductive structures, and halo currents closed partly through plasma periphery and partly through structures. This article describes various design features serving for suppression of eddy- and halo related EM loads in ITER. Parallel slits and various kinds of reshaping help suppress eddy related EM loads in massive parts such as shield blocks and first wall panels. A principle of force- and torque-free current paths is used in electrical straps passing pre-defined waveforms of halo and eddy currents. Multiple electro-insulating breaks were proven necessary to suppress eddy related EM loads at blanket manifolds. In all listed cases workable design solutions have been found in a frame of pre-defined tight interfaces.