Transients in D-T and D-³He Tokamak Fusion Reactors

A time-dependent, volume-averaged particle and power balance code is used to investigate reactivity transients during tokamak startup and after sudden changes in the plasma confinement, fueling rates, and impurity concentrations in deuterium-tritium (D-T) and D-³He fusion reactors. For a given H-mode factor f_H relative to the ITER89-P scaling law, a very narrow range of = _part^*/_E values, limited by quenching of the fusion burn due to ash accumulation and by exceeding operational limits, is found to sustain steady fusion burn. The dependence of the large power overshoot taking place shortly after ignition due to ash accumulation on the assumed and f_H is examined. To alleviate the excessive external heating power requirements for D-³He-reactor startup, schemes utilizing D-T fusion reactions are considered. Because of power transients of several hundreds of megawatts in reactors operating at a gigawatt level of fusion power, triggered by very small changes in the plasma confinement (