THE TUBULAR SEPARATE FIRST WALL FOR ITER-EDA

The first wall (FW) is one of the most loaded plasma-facing components ; the heat flux is such that the thermal stresses are the most importa nt design concern. In addition, the FW must resist the eddy current in duced during plasma disruption and the high pressure of the coolant an d should maintain its properties under a fast neutron flux (dose up to 3 MW m(-2)). The tubular solution is the most suitable to cope with t he thermal stresses; the use of a double wall reduces the risk of leak s inside the vacuum vessel by avoiding the growth of cracks through bo th walls: the soft brazing in between the walls stops the growth of cr acks from one tube to the other. The eddy currents induced in the tube s are low acid the halo current flowing poloidally in the tubes exerts a radial pressure which is supported by the blanket box via supportin g points provided in between the FW and the blanket. The tubes are pro tected with a coating of beryllium or boron carbide against the radiat ion heat load during disruption, and with a coating of copper against runaway electrons. Fins attached to the tubes are provided to cope wit h the change in the toroidal width of the FW along the poloidal direct ion. The fins are also protected by coatings. The tubes can be made of steel to resist a heat flux of up to 1 MW m(-2). For higher heat load s, copper or vanadium can be used. The tubular FW can be replaced inde pendently of the blanket. The thermohydraulic, electromagnetic and dyn amic analyses confirm the viability of the solution proposed.