TRANSIENTS IN D-T AND D-HE-3 TOKAMAK FUSION-REACTORS

A time-dependent, volume-averaged particle and power balance code is u sed to investigate reactivity transients during tokamak startup and af ter sudden changes in the plasma confinement, fueling rates, and impur ity concentrations in deuterium-tritium (D-T) and D-(3) He fusion reac tors. For a given H-mode factor f(H) relative to the ITER89-P scaling law a very narrow range of rho = tau(part)/tau(E) values, limited by quenching of the fusion burn due to ash accumulation and by exceeding operational limits, is found to sustain steady fusion bum. The depende nce of the large power overshoot taking place shortly after ignition d ue to ash accumulation on the assumed rho and f(H) is examined. To all eviate the excessive external heating power requirements for D-He-3-re actor startup, schemes utilizing D-T fusion reactions are considered. Because of pou er transients of several hundreds of megawatts in react ors operating at a gigawatt level effusion power triggered by very sma ll changes in the plasma confinement (\delta f(H)\ of the order of 1%) and fueling rates (\Delta S\ of the order of 10%), a quenching of the burn or a disruption can easily occur.