ITER CS Conductor Helium Inlet Design Optimization and Evaluation

The ITER central solenoid (CS) is wound from cable-in-conduit-conductor (CICC) and cooled by supercritical Helium (He) delivered to ~120 inner diameter (ID) turns through integrally welded "inlets." The flow to each inlet splits and passes through two pancakes, exiting at outlets. While both the He supply and return points (outlets) require penetrating the conduit wall, the inlets reside in the highest stress field, and thus become the more critical structural element.

The CS Conceptual Design Review (CRD) reference He inlet design has a long, narrow slot in the inside diameter (ID) turn wall with pencil-tip shaped ends. This shape is optimized in order to minimize the hoop stress concentration. The slot length is chosen to expose each of the six superconducting (SC) sub-cables to the He cooling supply. Implementing this design at 120 inlet sites requires substantial machining and welding operations where even virgin conduit has minimal structural margin.

A design space exploration produces numerous inlet options. One configuration emerges as the new reference configuration: the oblong, heavy-wall boss. It addresses all of the critical issues: bi-axial stress field, pressure drop and sub-cable flow uniformity, manufacturing costs (complexities and risks) and in-service robustness (least invasive, greatest margin).

Finite element (FE) simulations are presented which highlight the results of the optimization and evaluation process.