Transport, instability and disruptions in tokamaks

Instabilities are governed by transport-determined plasma profiles and transport is in turn affected by instabilities. A one-dimensional code has been developed which models this relationship. The dependence of magnetic island sizes on total current is described. Above a critical current, there is a non-linea interaction between the m = 1 and m = 2 modes which takes place through their effect on the current profile. This leads to a disruptive loss of confinement. Inclusion of the effect of impurity radiation leads to repeated soft disruptions at a lower current.