Sawteeth stabilization by energetic trapped ions
The problem of the effect of an energetic ion population on the onset of the kink-tearing modes is reviewed. Trapped energetic ions induce a stabilising effect by decreasing the Laplacian function in the MHD region on each side of the resonant layer. The effect is due to a resonant coupling of the mode with the trapped ions, if their precession frequency is larger than the mode frequency. It superimposes onto the interchange effect, which is destabilising for trapped ions, and which must be cancelled out by an equivalent population of circulating ions. The precise scenario of the stabilisation involves the response of the resonant layer. Linear regimes under the MHD constraint and in the classical tearing framework have already been studied. Here a non-linear situation, in the presence of a magnetic island with a small width delta, is considered. The stability requires that Delta' is less than K/delta where K/delta reflects the interchange effect in the resonant layer. The actual stability condition is Delta' less than K(D/nu(coll))(1/2), intermediate between the pure MHD condition (Delta'=infinity) and the classical tearing condition (Delta' = 0).
Bibliographic Reference: Paper presented: 18th European Conference of the EPS-Plasma Physics Division, Berlin (DE), June 3-7, 1991
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Record Number: 199110360 / Last updated on: 1994-12-02
Original language: en
Available languages: en