M. Onozuka, G. Johnson, K. Ioki, G. Sannazzaro, K. Takahashi T. Iizuka and
R. Parker
ITER Garching Joint Work Site, Boltzmannstr. 2, 85748 Garching, Germany
H. Neilson, Princeton Plasma Physics Laboratory, USA
K. Koizumi, Japan Atomic Energy Research Institute, Japan
E. Kuzmin, Efremov Institute, Russian Federation
B. Nelson, Oak Ridge National Laboratory, USA
C. Vallone, NET Team, Germany
Design of the Vacuum Vessel (VV) for the International Thermonuclear Experimental Reactor (ITER) has made substantial progress during the period of the Engineering Design Activity. The VV is part of the Tokamak-Basic Machine and provides the primary high vacuum and tritium boundary for the plasma. The VV is torus shaped and is located inside the cryostat. It is supported in the vertical direction by flexible rods suspended from the Toroidal Field (TF) coils. Lateral support is provided by toroidal links between each equatorial port and the adjacent TF coil. The blanket and divertor are mounted on the vessel interior and all loads are transferred through the vessel to the vessel supports. The VV is made from SS 316 LN-IG (ITER Grade) and has a double shell structure. The minor and major radii of the VV are 4.1 m and 13 m respectively, and the overall height is 14.5 m. The inner and outer shells are made from welded plates, 40 to 60 mm in thickness. The inner and outer shells and stiffening ribs between them are joined by welding, which gives the vessel the required mechanical strength. The total thickness of this structure is typically in the range of 0.45-0.82 m.
Recent design progress includes the modification of the inboard structure and the employment of ferromagnetic material between the VV shells. A cylindrical shape has been employed on the straight section of the inboard area that was originally designed as a polygonal cylinder. With this configuration, the structural integrity of the inboard region is further improved to resist the induced forces due to the fast current discharge of the TF coil.
Reduction of the toroidal field ripple is one of the crucial issues for large size tokamaks. Ripple reduction decreases the particle loss and energy loss of the injected neutral-beam particles and the a-particles. In order to reduce toroidal field ripple, inserts of ferromagnetic material for the VV have been proposed. Ferromagnetic plates replace shielding plates between the VV shells only beneath the outboard region of the TF coils.
The details of recent VV design progress are to be described in this symposium.