Fusion reactivities and power multiplication factors of beam-driven toroidal reactors with both D and T injection

Key reactor parameters of intensely beam-driven toroidal plasmas with 50: 50 D-T composition maintained by neutral-beam injection of both D and T, together with plasma re-cycling, are determined. The deuterons and tritons are injected with equal intensity and velocity. This mode of operation is most appropriate for high-duty-factor, high-power-density operation, in the absence of pellet injection. The velocity distributions of energetic D and T ions are calculated from a relatively simple slowing-down model, but include a tail above the injection velocity that results from energy diffusion. Fusion power multiplication Q and fractional tritium burn-up are determined from fusion reactivities calculated for beam-target, hot-ion, and thermonuclear reactions. For conditions where Q ∼ 1, beam-target reactions are dominant, but reactions among the hot ions contribute substantially to the total reaction rate when n hot /n e ≳ 0.2. To maintain the bulk-plasma temperature at progressively smaller n e τ E , it is necessary to continuously increase n hot /n e , so that reactions among energetic ions serve to maximize the Q-value and power density in low-n e τ E -driven operation.