Internal disruption = catastrophic ergodisation

Internal disruptions have been observed in tokamaks since 1973, and the best that one can say about their theoretical explanation is that there is still no consensus. Four main possibilities exist: a) Total reconnection, as proposed by Kadomtsev. b) Microturbulence triggered by a current singularity as proposed by Samain and Dubois. c) Field line ergodisation due to toroidal effects on the m=1 mode as proposed by Lichtenberg and Mercier. d) Interchange as proposed by Wesson. Theory a) is contradicted by experimental evidence (e.g. postcursors). Theory c) needs a very low central q value (q(0)≤.7). Theory d) needs a very high central q value (q(0)∼1-ε). Theory d) is incomplete and qualitative. Some recent experimental and theoretical results throw a new light on the problem. We will consider here only the simple sawteeth with an m=1 precursor, and present a more complete interpretation. (author) 7 refs., 2 figs