An analysis of the exhaust of a fusion reactor to a divertor target by collisionless processes

Abstract

An analysis is presented of the collisionless transport of particles and energy from a tokamak reactor plasma to a divertor target. Account is taken of the cooling effects of both unburnt fuel from the reactor and of secondary electrons emitted from the target. Even so, the temperature of the exhaust plasma is high and the potential of the target sheath exceeds the thresholds for unipolar arcing unless the burn-up fraction is impracticably low, i.e. f_B < 10⁻³. It would thus appear that the exhaust of a reactor by purely collisionless processes will pose formidable problems, and it is desirable to introduce additional mechanisms for cooling the electrons in the exhaust plasma.