Radiative power exhaust and plasma detachment*

Plasma power exhaust and particle handling are both critical issues in

steady-state and long-pulse power reactors. In the current short-pulse

machines, both issues appear to be interwined, but that is not the

case for power reactors. Broadly speaking, particle handling involves

the pump-out of unburnt fusion fuel and helim ash in the form of

neutral particles, and wall impurity production (wall erosion) due to intensive plasma-material

interaction. The essential requirement is simply plasma detachment at

the divertor plates, which facilitates plasma recombination at low

$T_e$ and reduced wall erosion with low ion energy.  The enhanced

radiation associated with divertor detachment can reduce the heat load

on the divertor, but the reduction is rather limited for the closeness

of the radiation zone to the divertor surface. For plasma power

exhaust, the challenge is that the plasma wetting area on the

divertor is too small to accommodate the overall plasma heating flux, so

it must be radiated to the larger area of the first wall from further

upstream. Here we will discuss the radiative and impurity transport physics

that would inform an integrated solution for both plasma power exhaust

and particle handling in a power reactor.