THEORY OF SAWTOOTH OSCILLATIONS
When sawtooth oscillations were first observed, theory had available an m=1 MHD mode to provide the required instability. Although the perceived form of this m=1 instability has changed over the years there has always been a plausible candidate available. With a view to the rapidity of the collapse, Kadomtsev's model provided an elegant solution, but recent experimental results have been in conflict with this model. The quasi-interchange model was suggested as an alternative. The model was apparently verified by observations on JET, but measurements of q-"o" on some other tokamaks give levels of magnetic shear which would not allow this mode. The other persistent problem related to the trigger is in a sense obvious, but it has only been formally recognised with the observation of precursorless sawteeth on JET. The question is therefore: how is the rapid growth rate gamma switched on in time of the order gamma"-1"? In addition, though the observations of monster sawteeth and the associated neutron sawteeth perhaps provide clues, they seem at present, only to add to the list of difficulties. Good experimental work will be an essential element in resolving the sawtooth problem.
Bibliographic Reference: REPORT JET-P(87)55, 1987, AVAILABILITY: JET, ABINGDON, UK
Record Number: 1989126080300 / Last updated on: 1989-05-01
Available languages: en