Minor and major disruptions as well as sawteeth oscillations (internal disruptions) were identified in the discharges of the small Tokamak TBR-1, and their main characteristics were investigated. The coupling of a growing m=2 resistive mode with an m=1 perturbation seems to be the basic process for the development of a major disruption, while the minor disruption could be associated with the growth of a stochastic region of the plasma between the q=2 and q=3 islands. Measured sawteeth periods were compared with those predicted by scaling laws and good agreement was found. The time necessary for the sawteeth crashes also agrees with the values expected from Kadomtsev's model. However, there are some sawteeth oscillations, corresponding to conditions of higher plasma Zeff, which showed longer crashes and could not be explained by this model.
Sawtooth oscillations in a small tokamak