The recent observations of sawtooth oscillations having a very fast collapse phase call for a re- examination of the theoretical description of sawtooth behaviour. One possibility is that the instability involved is an ideal m-1- "quasi-interchange" mode. A calculation of the stability of this mode shows that flattening of the q profile reduces the critical beta-p required for instability. Thus, contrary to previous expectations the ideal mode can be unstable even at the low values of beta-p observed experimentally. Non-linear simulations show the predicted cellular convection. The distinction between the behaviour of the quasi-interchange and a tearing mode is described and a comparison is made with experimental results from JET. Finally attention is drawn to a fundamental difficulty in explaining the rapid collapse in precursorless sawtooth oscillations.
Bibliographic Reference: 11TH INTERNATIONAL CONFERENCE ON PLASMA PHYSICS AND CONTROLLED NUCLEAR FUSION RESEARCH, KYOTO (JAPAN), NOV. 13-20, 1986 WRITE TO THE PUBLICATIONS OFFICER, JET JOINT UNDERTAKING, ABINGDON, OXON OX14 3EA (UK), MENTIONING REPORT JET-P(86)44, 1986
Record Number: 1989125079900 / Last updated on: 1987-12-01
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