A model for limiter heat flux protection by local impurity radiation
On the largest tokamaks the level of power launched into the discharge has reached tens of MWs. This has created a qualitatively new situation for the interaction of the edge plasma with material surfaces such as limiters or divertor plates. In particular, the phenomenon of carbon blooms has been discovered, characterised by a sudden increase of carbon particles being released into the discharge and a subsequent strong growth of energy losses by radiation. These carbon blooms are localised at hot spots on the wall with a surface temperature of more than 3000 K. In the present paper an attempt is made to model theoretically the thermal balance of the plasma at the limiter, by considering a cloud of radiating impurities in the vicinity of a hot limiter surface protecting the limiter surface from overheating. The dynamics of the impurity particles coming into the SOL plasma from the limiter are strongly coupled with the self-consistent electric field generated due to the presence of the impurity ions themselves. The length of the radiating cloud of charged impurities in the SOL near the limiter can be much more than the extent of the region of atom ionisation. When the limiter surface temperature exceeds the critical value T(W,c) at approx. 2100 C, the impurity radiation in the SOL near the limiter increases strongly, which stabilises T(W) at the level of T(W,c). This theoretical result is in good agreement with experimental data from TEXTOR.
Bibliographic Reference: Article: 18th European Conference on Controlled Fusion and Plasma Physics, Vol. III (1991) pp. 161-164
Record Number: 199111396 / Last updated on: 1994-12-02
Original language: en
Available languages: en