It is certainly not a thin, soft cover to keep the plasma warm. It is a thick, massive, complex structure that serves three major purposes: (1) capture the neutrons gener­ated by fusion and convert their energy into heat, (2) produce the tritium to fuel the DT reaction, and (3) shield the superconducting magnets from the neutrons. The blanket is divided into modules for easier replacement. Figure 9.9 shows where the blanket is located inside a tokamak. In Fig. 9.9a, we see that the plasma first strikes the first wall (FW), which is also the front surface of the blanket. Then, the neutrons go into the blanket, where their energy is captured, and where the tritium breeding takes place. The heat is taken away by hot gas or liquid coolants to heat exchangers outside. Shielding material protects the vacuum walls and supercon­ducting magnets from the heat and the neutrons. Figure 9.9b gives an idea of how the blanket surrounds the plasma and lies inside the vacuum. Outside the vacuum vessel are the magnetic coils. The Central Solenoid coil is critical, since there is not much room in the hole of the torus to fit this coil into. The symmetry axis of the torus is at the left. The entire machine fits inside a cryostat which insulates the mag­net coils from the outside world, keeping them at superconducting temperatures.

In a reactor there could be hundreds of blanket modules, each weighing a ton. There are many ideas for blanket design, and ITER will have three ports available for test blanket modules (TBMs). There are six TBM proposals competing for these three spots [5].