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The electromagnetic perturbation produced through a set of antennae in a Tokamak plasma is studied near the ion cyclotron resonances and the two ion hybrid resonance. Using an appropriate variational principle, it is possible to derive the perturbed field (the compressional wave and the converted torsional wave) with the help of relatively smooth test functions of compressional type. The method produces conditions under which the variational functional L, extremum with respect to the perturbation, can be written in a suitable manner for computer handling. Moreover, this functional provides an expression of the power damped by the thermal motion of particles and in the two ions hybrid regime provides the power coupled on the converted wave. The ion cyclotron resonance leads to different regimes upon the ratio of the parallel scale length lambda of the field and the parallel scale of the resonance lambda-c, lambda-c about v-th/V-//omega-c/**1/2. The usual WKB formulas used by previous authors appear limited to the case lambda < lambda-c only and new formulas are given for lambda>=lambda-c. In the mode conversion case the method generalizes the Budden's results, with restrictions taking into account the non uniformity effects along the resonance surface.

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Bibliographic Reference: WRITE TO CEA MENTIONING REPORT EUR-CEA-FC-1214 EN, 1983
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