Transit radiative cooling by injected impurities

For long-pulse and steady-state fusion reactors, neutral gases of

deuterium/helium and impurities like neon are introduced into the

plasma for radiative power exhaust further upstream and for particle

exhaust via plasma detachment at the divertor plates. These injected

neutral particles would undergo ionization and be assimilated into the

plasma, which due to edge/boundary plasma transport, acquire finite

residence time in the plasma. To achieve steady-state operation, the

finite residence time requires recirculation that involves continuous

injection at upstream and recycling at the downstream. Although the

overall plasma is in steady-state, individual injected particles

undergo collisional-radiative processes that turn an initial neutral

particle to charged ions that depend on the variation of the local

plasma density and temperature. The effectiveness of radiative cooling

by the injected particles can be gauged by the total radiated energy

over the residence time of the injected particle, which is a key

design parameter to optimize the location and rate of the injection

scheme, as well as the choice of the impurity species. Here we perform

time-dependent collisional-radiative modeling of the impurity

injection for radiative power exhaust in reactor plasmas.