The two time-scales of the sawteeth precursors
In TEXTOR, the sawtooth period is of the order of 15-20ms and precursors have been seen to develop within a few milliseconds prior to the central temperature crash. This report attempts to characterise this instability by the very different growth rates in the course of one sawtooth period, in view of the long magnetic diffusion time-scale and the instability of the tearing mode. An equation is established for the jump of the derivative of the magnetohydrodynamic (MHD) solution across the singular q=1 layer for current profiles with a slope discontinuity and a small shear. It is found that the growth rate of the sawtooth trigger can pass from resistive to MHD values for slight variations either of the shear or in the position of the slope discontinuity. These profile properties have been observed in sawtoothing TEXTOR discharges.
Bibliographic Reference: Article: Nuclear Fusion, Vol. 29 (1989) No. 7, pp. 1175-1180
Record Number: 199010421 / Last updated on: 1994-12-01
Original language: en
Available languages: en