ITER central solenoid alternate pre-compression structure - Concept and analysis

The ITER Central Solenoid (CS) is comprised of six independent coils held together by a pre-compression support structure. This structure must provide enough preload to maintain sufficient coil-to-coil contact throughout the current pulse. End of burn (EOB) represents one extreme time-point when the currents in the CS3 coils oppose those of CS1 & CS2. The present baseline design uses nine tie plate pairs located on the coil ID and OD to achieve this pre-compression. While this is an efficient structural approach, the outer tie plates limit access to the coil OD and result in very tight tolerances over the 12.75 m tall toroidal field (TF) coil bore. An alternative pre-compression structure has been developed by the US ITER Project Office, which addresses both of these issues using only internal tension members. This allows clear access to the outer CS surface for plumbing and current feeders, and more reasonable OD tolerances. In addition, the Tension Rod pre-compression structure utilizes existing technology (such as hydraulic tensioner or Superbolt®), which streamlines initial preloading and subsequent adjustments. Structural and transient electromagnetic FEA of the tension rod concept demonstrates that the stresses, displacements, and preliminary Eddy current heat loads are within allowable limits. Fabrication estimates demonstrate no additional cost of the tension rods compared to the tie plates.