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It was recently claimed that in nonlinear coherent drift wave theory the temperature gradient k(T) = d lnT/dx is irrelevant and that, instead of k(T), the derivative dk(n)/dx of the density gradient k(n) = d lnn/dx (with a factor T/u) determines the nonlinearity. It is shown that this claim is erroneous in general and is caused by neglecting the space dependence of the phase velocity of the waves. The inhomogeneity of the refractive index for drift waves is approximately k(T)-(dk(n)/dx)T/u. The case k(n)(x)T(x)=const. is, therefore, special in two respects: the plasma does appear homogeneous to the waves, but also the disparate nonlinear terms coincide. In the generic case, however, n(x) and T(x) are independent profiles, and the temperature gradient nonlinearity is responsible for quasi-one- dimensional soliton-like waves. Their duration, however, is limited by the inhomogeneity of the refractive index.

Additional information

Authors: SALAT A, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP 6/291 EN (1990)
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
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