Finite Element Analysis of the Energized ITER TF Coil in Test Conditions

The ITER magnet system comprises 18 superconducting Toroidal Field Coils (TFC) based on Nb₃Sn conductor supplied with the operational nominal current of 68 kA to produce a toroidal magnetic field of 5.2 T at the plasma major radius R = 6.2 m. A Magnet Cold Test Bench (MCTB) to test the TFC at 4 K up to a current value of 68 kA is under construction at ITER Organization (IO) site. The foreseen test conditions are substantially different from those corresponding to the 18-coil operation as the coils will be tested individually in horizontal position and supported at a few locations along the case. On the one hand, the magnetic field distribution produced by one single coil yields a different pattern of Lorentz forces. On the other hand, the absence of case wedging results in a reduced structural stiffness of the analyzed system. Finite element analysis work on this subject has been reported in the past for the TF Winding Pack (WP) after impregnation without undergoing the enclosure in the case, showing that the TF WP could be tested in safe conditions at a reduced energization of 15 kA (20% of the nominal current). This work considers currents up to the nominal 68 kA and the TF case which provides additional stiffness to the coil. Prior to the energization load, the coil is subject to gravity and cooled down to 4 K.

I. Introduction

The Iter magnet system includes 18 Nb₃Sn Toroidal Field (TF) coils to confine the plasma, a Nb₃Sn Central Solenoid (CS) divided in 6 modules to induce the plasma current, 6 NbTi Poloidal Field (PF) coils to control its shape and position, and a set of Correction Coils (CC) to compensate the field errors due to misalignment during assembly. The TF coils will be energized at a nominal current of 68 kA to produce a toroidal magnetic field of 5.2 T at the plasma major radius, yielding a peak field of 11.8 T at the Winding Pack (WP) in the inboard leg. The large inwards radial force around 400 MN arising during operation due to the interaction between the toroidal magnetic field and vertical current will be reacted by the TF case and wedging of the inboard leg (50 MN/m).