Design and Analysis of the ITER Vertical Stability (VS) Coils

Abstract

The ITER vertical stability (VS) coils have been developed through the preliminary design phase by Princeton Plasma Physics Laboratory (PPPL). Final design, prototyping and construction will be carried out by the Chinese Participant Team contributing lab, Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The VS coils are a part of the in-vessel coil systems which include edge localized mode (ELM) coils as well as the VS coils.The VS design employs four turns of stainless steel jacketed mineral insulated copper (SSMIC) conductors The mineral insulation is Magnesium Oxide (MgO). Joule and nuclear heat are removed by water flowing through the hollow copper conductor. The slightly elevated temperatures in the conductor and its support spine during operation impose compressive stresses that mitigate fatigue damage. Away from joints, and breakouts, conductor thermal stresses are low because of the axisymmetry of the winding (there are no corner bends as in the ELM coils).The joints, and break-out or terminal regions are designed with similar but imperfect constraint compared with the ring coil portion of the VS. The support for the break-out region is made from a high strength copper alloy, CuCrZr. This is needed to conduct nuclear heat to the actively cooled conductor and to the vessel wall. The support “spine” for the ring coil portion of the VS is 316 stainless steel, held to the vessel with preloaded Inconel 718 bolts. Lorentz loads resulting from normal operating loads, disruption loads and loads from disruption currents in the support spine shared with vessel, are applied to the VS coil. Stresses in the coil, joints, and break-outs are presented. These are compared with static and fatigue allowables. Design for fatigue is much less demanding than for the ELM coils. A total of 30,000 cycles is required for VS design.