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Magnetic coordinates for hydromagnetic equilibria are defined which treat toroidal and "straight" helical plasmas equivalently yet exploit the existence of a continuous symmetry to derive relations between various geometrical and physical quantities. This allows the number of equilibrium quantities which must be known to be reduced to a minimal, or primitive set. practical formulae for various quantities required in hydromagnetic stability calculations (interchange, ballooning, and global) are given in terms of this primitive set.•Permanent address:

The coupling of ICRF power from a slow-wave antenna to a plasma with finite temperature is examined. A heuristic model, allowing explicit representations of ion Bernstein waves, fast waves and slow waves, is used to clarify how the antenna power is partitioned into the various wave energy fluxes. This model is complemented quantitatively by a more elaborate and realistic computer model. It is shown that such antennas can be highly efficient in transferring most of the antenna power directly to ion Bernstein waves, with only a very small fraction going into fast waves. The potentiality of this coupling scheme for plasma heating in ICRF is briefly discussed.

Parametric decay of magneto-acoustic oscillations in a cylindrical plasma column is considered, including the Hall effect and the effects of finite resistivity. Growth rates for axisymmetric modes in decay instabilities are derived and applied to the problems of parametric excitation of Alfvén waves and supplementary heating of plasmas. It is shown that both the slow (ion cyclotron) and fast (compressional) modes may be parametrically excited. The threshold &litudes for nonlinear dissipation of pump field energy are calculated and briefly discussed.

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