Stability of toroidicity induced drift waves in divertor tokamaks
The stability of toroidicity induced drift waves in a tokamak equilibrium with magnetic separatrix is studied both analytically and numerically. In particular, the task of a proper determination of the complex ballooning parameter Ú(0) is performed by solving the stationarity condition for the eigenvalue. Results show qualitative dependence on the location of the x-point in the meridian plane. Specifically, locating the x-point in the equatorial plane, both on the outside and on the inside of the plasma, causes a deepening of the well structure in the potential for the eigenmode, so enforcing the inhibition of the shear damping and the marginal stability result obtained in the circular magnetic surfaces case. On the other hand, the location of the x-point at the top of the plasma produces a flattening of the well and restores the shear damping, yielding stabilisation of the mode. A new quasi-marginally stable branch, corresponding to modes localised around the x-point, is shown to exist at high values of the separatrix parameter k and x-point location close to the equatorial plane.
Bibliographic Reference: Report: RT/FUS/88/16 EN (1988)
Availability: Available from Servizio Studi e Documentazione, ENEA, Centro Ricerche Energia Frascati, C.P. 65-00044 Frascati, Roma (IT)
Record Number: 198911010 / Last updated on: 1994-12-01
Original language: en
Available languages: en