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Various ICRH scenarios for ITER-FEAT are evaluated. A wave propagation and damping study confirms the potential of the second harmonic tritium heating scenario for both heating and current drive purposes. The fundamental deuterium heating scheme is dominated by beryllium and alpha particle absorption. Owing to the reduced ITER size, the low frequency current drive window is lost in practice. A 3He minority greatly enhances the performance. In the early stage of the discharge, the power absorbed by the 3He is transferred to the background ions but, later on, the power of the fast particles (from both the 3He and the tritium tails) is roughly equally distributed between electrons and ions. Using the experimentally established expression for the L to H mode threshold, it is found that the H mode regime can always be reached using RF heating. To achieve Q = 10, high density operation is required. Minority current drive competes with heating and with electron current drive. The scenarios foreseen for the non-activated ITER-FEAT phase are also discussed.

The performance on plasma of the antennas of the proposed ITER ICRF system is evaluated by means of the antenna 24 × 24 impedance matrix provided by the TOPICA code and confirmed and interpreted by the semi-analytical code ANTITER II (summarized in an appendix). From this analysis the following system characteristics can be derived: (1) a roughly constant power capability in the entire 40–55 MHz frequency band with the same maximum voltage in the eight feeding lines is obtained for all the considered heating and current drive phasings on account of the broadbanding effect of service stubs. (2) The power capability of the array significantly depends on the distance of the antenna to the separatrix, the density profile in the scrape-off layer (SOL) and on the strap current toroidal and poloidal phasings. The dependence on phasing is stronger for wider SOL. (3) To exceed a radiated power capability of 20 MW per antenna array in the upper part of the frequency band, with a separatrix–wall distance of 17 cm and a conservative short decay plasma edge density profile, the system voltage stand-off must be 45 kV and well chosen combinations of toroidal and poloidal phasing are needed. (4) On account of the plasma gyrotropy and of poloidal magnetic field, special care must be taken in choosing the optimal toroidal current drive and poloidal phasings. The ANTITER II analysis shows furthermore that important coaxial and surface mode excitation can only be expected in the monopole toroidal phasing, that strong wave reflection from a steep density profile significantly reduces the coupling even if the separatrix is closer to the antenna and that the part of the edge density profile having a density lower than the cut-off density pertaining to the considered phasing does not significantly contribute to the coupling.

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A variational principle for studying one-dimensional wave propagation and damping near the ion-ion hybrid conversion region in a tokamak is presented. In its variational form, the wave equation is closely related to the power balance equation: substituting the electric field for the test function in it yields the generalized Poynting theorem. The guiding centre position rather than that of the particle is adopted as the independent variable. Toroidal and oblique incidence effects are retained but the poloidal magnetic field is neglected. A strictly positive power density for Maxwellian plasmas is ensured by starting from a general formalism due to Lamalle (Lamalle PU 1993 Phys. Lett. 175A 45;1997 Plasma Phys. Control. Fusion 39 1409 and expanding the operator acting on the electric field in the expression for the absorbed power per guiding centre orbit (rather than expanding the dielectric tensor, as is usually done) in terms of the assumed small parameter ε = k ⊥ ρ, where k ⊥ is the perpendicular wavenumber and ρ the Larmor radius. The general formulae for the dielectric response are provided and explicit expressions are given for the case where up to second-order corrections in ε are retained in the operator. As an illustration, the absorption of radio frequency power in a (H)-D-(Ar) TEXTOR plasma typical for the radiative improved mode is discussed.