An asymptotic analysis of the radiation pattern of ion cyclotron resonance heating antennas

Using the stationary phase method, a simple asymptotic analysis of a two-dimensional model of the coupling of the cold-plasma magnetosonic wave excited by an ion-cyclotron resonance heating (ICRH) antenna is presented. Such an analysis allows quick evaluation of the basic characteristics of the ICRH antenna radiation pattern and shows how the power spectrum radiated by the antenna and plasma dispersion properties combine to produce the power flux distribution observed in the far-field region. The results of the present simplified analysis are found to be in reasonably good agreement with more sophisticated coupling codes. This development thus serves as a simple analytic tool for quick investigation of the most fundamental features of coupling for antenna design studies. With a view to spectrum shaping for improved heating and tokamak RF current drive, the case of a phased antenna array is also analysed.