In the Tokamak devices, the First Wall (FW) is a Plasm Facing Component devoted to absorb part of the plasma power, shielding the Vacuum Vessel and other In Vessel Components (e.g. coils, diagnostics etc.).
In the DTT facility, the FW consists of three main components: the Inboard (IFW), the Outboard (OFW) and the Top FW (TFW). The FW is poloidally segmented to have small impact on the volume of the vacuum chamber in order to accommodate as many plasma scenarios as possible.
The TFW is segmented in modules having a toroidal extension of 20°. Poloidally, the TFW is composed of two adjacent modules, positioned respectively at a smaller (module A) and at a larger radius (module B, Fig. 1). The poloidal segmentation, needed for the extraction of the modules from the machine through the equatorial ports, was studied to allow the replacement of only module A, in case of the presence of a superior divertor required to allow experiments on double null scenarios even at high power.
The module A is the closest to the plasma and the most exposed to high thermal loads due to plasma disruption. For this reason, three solutions were considered for its design (Fig. 2, 3 and 4). The proposed solutions includes a tungsten-coated steel panel, which is simpler to manufacture and with lower cost, and two with monoblock tungsten arrays (coaxial or single-tube divertor). The panel solution requires the introduction of W-thick ribs as protection from disruption; the monoblock designs, with an apparent higher cost, can withstand disruption and would allow experimentation with double null scenarios (even if at reduced power).
Verifications are ongoing to select the reference module A TFW concept.
Fig. 1 Overview of the Divertor tokamak test facility
Fig. 2 – Tokamak machine assembly
Fig. 3 – Overview of Tokamak building with ancillary plants
Fig. 4 – Lower radius TFW module: plate-based design.