The ITER experiments will take place inside the vacuum vessel, a hermetically sealed steel container that houses the fusion reactions and acts as a first safety containment barrier. In its doughnut-shaped chamber, or torus, the plasma particles spiral around continuously without touching the walls.
The vacuum vessel provides a high-vacuum environment for the plasma, improves radiation shielding and plasma stability, acts as the primary confinement barrier for radioactivity, and provides support for in-vessel components such as the blanket
and the divertor
. Cooling water circulating through the vessel's double steel walls will remove the heat generated during operation.
Forty-four openings, or ports, in the vacuum vessel provide access for remote handling
, and vacuum
systems. (Neutral beam injection will take place at equatorial level, for example, while on the lower level, five ports will be used for divertor cassette replacement and four for vacuum pumping.)
The blanket modules lining the inner surfaces of the vessel will provide shielding from the high-energy neutrons produced by the fusion reactions. (Some blanket modules will also be used at later stages to test materials for tritium breeding
concepts.) Along with the magnet systems, the ITER vacuum vessel is entirely enclosed in a large vacuum chamber called the cryostat
In a tokamak device, the larger the vacuum chamber volume, the easier it is to confine the plasma and achieve the type of high energy regime that will produce significant fusion power.
The ITER vacuum vessel, with an interior volume of 1,600 m³, will provide an absolutely unique experimental arena for fusion physicists: the volume of the plasma contained in the centre of the vessel (840 m³) is fully ten times larger than that of the largest operating tokamak in the world today. The ITER vacuum vessel will measure 19.4 metres across (outer diameter), 11.4 metres high, and weigh approximately 5,200 tonnes. (With the installation of the blanket and the divertor, the vacuum vessel will weigh 8,500 tonnes.)