Activity is underway in all areas of Europe's 257-metre-long winding facility, as the elements of poloidal field coil #5 (PF5) are advancing through the impregnation and stacking phases, and the winding tables have begun to turn again for PF2.
Winding: With a few adaptations, the equipment set up to wind the first production coil, PF5, can serve again to wind the double pancakes required for PF2, as both coils measure 17 metres in diameter. However the two coils are siblings, not twins. They differ in the number of turns, or spires, per double pancake (10 for PF2; 14 for PF5) and in the number of double pancakes per coil (6 for PF2; 8 for PF5). As a consequence, PF5 will be much heavier than PF2—350 tonnes vs 204 tonnes. In February, European contractors began winding the first double pancake for PF2.
Stacking: Following vacuum pressure impregnation (VPI) with epoxy resin—a process that imparts rigidity to the double pancake and ensures electrical insulation—the double pancakes are stacked to form the coil. For PF5, five out of a total of eight double pancakes have successfully completed VPI and are now stacked. The teams must then connect the pancakes to ensure the flow of cryogenic helium—both between the double layers of each pancake (an "intra pancake joint"), and between each double pancakes (an "inter pancake joint").
Dummy: Once all double pancakes are stacked and joined, another VPI resin-impregnation operation is performed on the entire assembly to create the "winding pack"—the very core of the coil. Just like for the earlier impregnation operation on individual double pancakes, the operation contributes both to electrical insulation and structural strength. The procedure will be tested on this short mockup section of a dummy PF5 winding pack.
Cold testing: At the end of the manufacturing process, the completed coil is placed into a toroidal vacuum chamber (or "cryostat") and cooled to cryogenic temperature in order to monitor thermal stresses and detect potential leaks in the helium piping. The large cryostat for PF5 and PF2 is already assembled (background); a smaller one is under construction in the foreground for PF6—the 10-metre-in-diameter coil that is being manufactured in China under a contract from Europe. PF6 is expected to be delivered to ITER in November.
