An important milestone for DTT project has been achieved: as part of the contract for the supply of 18 DTT Toroidal Field Coils (shortly TFC, Figure 1), ASG Superconductors has completed the first winding pack (shortly WP-01, Figure 2)

The WP is the core of a TFC. Large currents flowing through it create a toroidal magnetic field, which acts as a magnetic cage for the plasma. In the case of DTT TFC, the current flowing in each of the 84 turns constituting the winding pack is 42.5 kA and the magnetic field is 5.9 T at 2.19 m from the center of the machine in vacuum. 

In terms of engineering current density DTT TFC are presently the most demanding TF coils designed and manufactured for a tokamak machine with the Nb₃Sn superconductors.

The DTT TF winding pack consists of 5 double pancakes made of cable in conduit conductors (CICC) containing 420  Nb₃Sn strands and 180 Copper strands. To arrive to the milestone here celebrated, several qualification and production steps have been successfully passed. Indeed, the winding passes through the bend of the conductor to form double D-shaped pancakes (shortly DP). 

The DPs are then heat treated in a furnace at about 650°C to form the intermetallic compound Nb₃Sn that becomes superconductor at cryogenic temperature. After, the DPs are wrapped with a glass tape to achieve the specific insulation of the turns. Then, the insulated DPs are stacked together to form the winding pack but then the WP is subject to in vacuum impregnation process with epoxy resin aimed at filling the gaps and producing a composite insulating material between the turns. 

At every step of the manufacturing process, stringent electrical and metrological tests are carried out in order to guide the fabrication towards the final result that shall respect the requirements for the shape tolerances and electrical resistance.

The first WP will be followed by the remaining 17 at a rate, in full swing, of one every 1.5 month. The expected completion date is then currently mid-2027. 

Figure 3 shows the two teams in charge of the contract from both DTT and ASG Superconductors posing in front of the WP-01 after the final tests in La Spezia. 

The following table summarizes some of the main geometrical and electrical properties of the WP.

Figure 1 - Rendering Image of a Toroidal Field Coil

Figure 2 - WP-01 exiting from the vacuum chamber after the final electrical tests

Figure 3 - The DTT and ASG contract responsible teams posing in front of the WP-01