The vacuum vessel (VV) is torus-shaped and double-walled. The double-wall cavity is filled with borated water to enhance the neutron shielding capability of the vacuum vessel. Every 40 degrees, the vessel is attached at the bottom to a gravity support.

The vacuum vessel can be baked at 200°C by means of heated nitrogen gas after draining the borated water. Plasma operation during VV baking is not planned because the neutron shielding capability would be lost and there would be too high a heat load on the cryogenic system.