CRITERIA AND DESIGN TRADE-OFF ISSUES FOR ITER

While the determination of the optimum parameters for a tokamak involves the complex trade-off of a large number of engineering and physics constraints, the overall dimensions are actually determined by a relatively simple set of criteria. These criteria are based on the tokamak radial build and elementary physics and engineering requirements, including guidelines for nT-tau(E), the aspect ratio, A = R/a, the edge safety factor, q(psi)95%, the plasma elongation, the size of the neutron shield, and the peak field at the toroidal field coil. Two of these parameters, the aspect ratio and plasma elongation, can be chosen so as to optimize the design parameters and minimize the size and cost of the tokamak. The ITER design point of R approximately 6 m and a approximately 2 m follows from these constraints and the parameter choices for aspect ratio and elongation.