Design of the Burning Plasma Experiment Vacuum Vessel

The Burning Plasma Experiment (BPX) is being designed to determine the physics behavior of self-heated fusion plasmas and demonstrate the production of substantial amounts of fusion power. The machine is designed to operate with a plasma current of 11.8 MA and a toroidal field of 9 T. The machine will have a major radius of 2.59 m and will have a fusion power of 100 -500 MW. The interior surface area of the vessel is about 150 m2. The high power density on the divertor plates requires the use of pyrolytic graphite. Most of the remainder of the metallic surface of the vessel is covered with either carbon fiber composite or graphite tiles. The operating temperature of the vacuum vessel is chosen to be 350 °C because of the good experience of JET and JT-60 with graphite tiles and operation at similar temperatures. The high plasma current, large stored energy, and large toroidal field give rise to large forces on the vacuum vessel during plasma current disruptions. These forces, together with the operating temperature, require the use of Inconel for the vacuum vessel structure. Even with the high strength of Inconel, thicknesses of up to 90 mm are required to have acceptable stress in the vacuum vessel shell. The vacuum pumping speed on BPX is limited to about 7000 l /s (N2 by the size of the access ports on the vessel and by remote handling considerations. The vacuum vessel can be baked to temperatures up to 550 °C without significant changes in the Inconel material properties. The requirements for outgassing of the vacuum vessel and the plasma facing components are discussed.