Fokker-Planck/Transport Studies of the Tokamak Fusion Test Reactor

The time-dependent behavior of neutral beam-heated DT plasmas in the Tokamak Fusion Test Reactor (TFTR) has been investigated with a numerical one-dimensional transport model, coupled with a fully nonlinear Fokker-Planck analysis of the injected energetic ions, a Monte Carlo neutral transport model, and a self-consistent beam-deposition code. The transport equations use diffusivities and conductivities consistent with those measured in present day tokamak devices. Two modes of operation are compared: mode I with D° beam injection, T° gas injection, and a high recycling coefficient; mode II with both D° and T° beam injection, no gas injection, and a low recycling coefficient. At lower beam powers, mode II yields the highest values of fusion power gain Qp. At higher beam powers, which are accompanied by higher plasma density, mode I yields the highest Qp. When a larger recycling coefficient is used in mode II, the Qp values are comparable, and Qp ≿ 1 is attainable with about 20 MW of beam power. The TFTR fusion performance is found to be very sensitive to the assumed diffusion rate of the bulk ions and moderately sensitive to variations in the ion thermal conductivity and in the diffusion rate of the energetic ions.