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The general kinetic description of two wave interaction in plasmas, obtained by perturbation expansion of the kinetic equation, is discussed along with various approximations. The general expression involves the full detail of the distribution function perturbations of the two interacting waves, and is at present numerically intractable. By replacing the general expression by a truncated expansion in velocity space, the low temperature kinetic (LTK) model is obtained. This model is valid when thermal effects are small for the scattered wave but makes no assumptions about interacting waves. Alternatively the LTK model may be derived from a truncated sequence of moments equations. It is found that the perturbation expansion must be carried out in variables which are linear in the distribution function. If the perturbation expansion is carried out in fluid velocity, which is non-linear, then the limitations of the truncated model apply also to the interacting waves. This is the principal cause of the limited range of applicability of the traditional cold fluid model of scattering. Finally, the consequences of linear dependencies and cross-correlations between fields and moments are considered.

Additional information

Authors: BINDSLEV H, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(94)71 EN (1994) 11 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
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