ICRF fundamental minority heating in inhomogeneous tokamak plasmas

Abstract

A theoretical model for the investigation of the ICRF fundamental minority plasma heating scheme in tokamak configurations is developed. The wave differential operator is obtained by including in a selfconsistent manner the effects of strong wave damping, linear mode conversion and a one-dimensional non-uniform equilibrium configuration. It is found that the use of a self-consistent equilibrium distribution function yields important modifications of the ICRF wave differential operator applicable to this heating regime. In particular, the paper presents a set of new terms which are resonant at the fundamental cyclotron frequency and which ensure the self-adjointness of the resulting wave operator in the limit k‖ → 0. A numerical scheme is developed with which solutions for the ICRF electromagnetic field and the corresponding power deposition and energy flux profiles can be obtained. An extensive parametric study is carried out for a range of wave and plasma parameters illustrative of current and proposed JET operating regimes. The results are considerably different from those obtained using a WKB fast wave model. In particular, the ‘full wave’ model presented in this paper yields a percentage for the wave power absorbed by the ionic species which is much larger than the one predicted by the WKB theory. The model presented also shows that the majority species can absorb a much higher proportion of the incident wave power than previously reported. Finally, the results obtained for JET indicate that in the case of low magnetic field incidence a sizeable percentage of the launched wave energy can be reflected on the fast wave branch for values of k‖ ≤ 6 m−1 and that at higher plasma temperatures electron heating becomes appreciable.