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This paper discusses the structure of drift waves in a rotating toroidal plasma. The rotation destroys an underlying symmetry that is the basis for the conventional ballooning representations of perturbations in a torus. An alternative description exploits the residual symmetry that persists despite rotation. It shows that sheared rotation annuls the toroidal coupling between perturbations associated with different magnetic surfaces, so that cylinder criteria rather than toroidal ballooning criteria again become relevant. Sheared rotation reduces the radial model width, and presumably therefore the anomalous transport. Another description of perturbations leads, as is well known, not to eigenmodes but to perturbations with a Floquet like time dependence on a magnetic surface. We show that this Floquet solution actually conceals an arbitrary time dependence of the perturbation! At the usual leading order in a high mode number expansion, the Floquet form and the eigenmode form are equivalent and are equally valid descriptions. However, in more accurate theory only the eigenmode form persists. The Floquet form, and its short term growth rate, should be regarded as transients associated with particular starting conditions and with the use of an idealized (linear) velocity profile.

Additional information

Authors: TAYLOR J B, AEA Fusion, Culham Laboratory, Abingdon, Oxon. (GB);WILSON H R, AEA Fusion, Culham Laboratory, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: 328 EN (1996) 15pp.
Availability: Available from the Librarian, UKAEA, Culham Laboratory, Abingdon, Oxon, OX14 3DB (GB)
Record Number: 199610657 / Last updated on: 1996-06-10
Original language: en
Available languages: en
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