Divertor Engineering for the ARIES-I Reactor^†

The ARIES tokamak-reactor design study is a multi-institutional project investigating several different visions of the tokamak as a commercial power reactor. The ARIES-I reactor design incorporates modest extrapolation of existing physics with advanced technology in the fusion power core (FPC) design. Use of aggressive technology such as high-field magnets and low-activation silicon-carbide (SiC) composites help to make ARIES-I an attractive reactor with excellent safety characteristics. The ARIES-I reactor uses a double-null poloidal-field (PF) divertor for particle exhaust and impurity control. Control of the edge-plasma density and temperatures has reduced the energy of the incident particles at the divertor to ∼20 eV, which is below the self-sputtering threshold for the tungsten target surface material. The target is constructed of SiC composite tubes with a 2-mm-thick plasma-sprayed coating of tungsten on the plasma-facing side and a 0.5-mm chemical-vapor deposited (CVD) coating of SiC on the back. The divertor is cooled by helium at lOMPa with inlet/outlet temperatures of 350°/650°C. In removing the divertor surface heat flux of 4.5 MW/m², a design safety factor of 1.8 is achieved. The divertor has a waste disposal rating of 0.10 (see text for definition), thus allowing Class-C shallow land burial, and a site boundary dose of 11.2 rem during an accidental release. Isotopic tailoring of the tungsten and target replacement every two years is necessary to achieve these safety characteristics.