Structural analysis and optimization of the break-out & feeder of the ITER lower vertical stabilization coil

• The break-out and feeders are analyzed using one model for the first time.
• Stresses derived from electromagnetic and thermal loads are mainly researched.
• Installation of additional sleeves is the effective method to solve the critical issue of too high stresses.
• Block structures can significantly eliminate singularities on the coil break-out.

Break-out & feeder is an essential component connecting the ITER lower vertical stabilization (VS) coil to the outside power source. It plays the role of interface between the in-vessel and out-vessel devices and has large influence on the coil performance. Due to the special location of the ITER lower VS coil, the break-out & feeder has to endure severe in-vessel environment such as high temperature, strong magnetic field and neutron irradiation. High temperature and restricted cooling paths can easily make the break-out under high thermal stress. While square crossing with the Tokamak toroidal magnetic field will result in large Lorentz forces in the feeders. Structural analysis of the break-out & feeder shows overlarge thermal stress concentrating in the coil spine where the conductors lead out. The primary stresses in the feeders are also extremely high. Moreover, there is difference in loading in comparison with the coil main body, which is designed to be mainly in compression and with relaxed crack growth issues, the break-out & feeder is not so compressive and will endure large tensile stress in work. Therefore, relieving the high stresses is important for its design. According to the results of further analysis, structure optimizations such as using block structures in the break-out and modifying the feeder supports are proved with good effect.