Special Engineering Problems of TFTR

Design of the TFTR presents special engineering problems as a result of constraints posed by the physics requirements of the fusion experiments. The ratio of plasma major and minor radii and the associated magnetic field strength required to achieve desired plasma conditions, the required confinement time, the two-component plasma concept, the complications of providing shielding from the 14 MeV neutrons and the necessity to control the inventory of tritium fuel, all constitute problems which, often, in actuality, must be approached as materials problems. The complex, precision structures must satisfy various criteria, for example, low magnetic permeability, high electrical resistivity, resistance to neutron activation and high damage tolerance. Another constraint in the engineering design of TFTR is the requirement to optimize access to machine components for maintenance and repair. Many of the problems associated with accessibility have been resolved: the vacuum vessel has been designed as a ten-segment vessel; the igloo shielding of the machine is composed of interlocking blocks of boron-loaded concrete; the center column is designed in three segments. Current engineering emphasis is on finalizing design of the toroidal field coils, lower poloidal field coils, vacuum vessel liners and limiters, and peripheral systems such as the vacuum pumping system and arrangement of diagnostics.