Power deposition profiles and poynting vector distribution of phased antenna arrays in the ion-cyclotron resonance heating of a net/intor-type tokamak

The heating produced by magnetosonic waves launched from phased antenna arrays in the ioncyclotron range of frequencies is studied for a large tokamak with NET/INTOR-like parameters. The model used combines a 3-D planar, cold-plasma, antenna-plasma coupling code and a 3-D non-circular, toroidal, hot-plasma/ ray-tracing code. First, the fractional power absorption of a ray during a single transit through the absorption layer is studied in a D-T plasma indicating total absorption in all INTOR cases except during the initial state characterized by low plasma temperature and density. However, in this case the single-pass wave absorption can be increased considerably by adding a few per cent of hydrogen. Further, complete power deposition profiles and Poynting vector distributions are presented for ‘symmetric’ and ‘antisymmetric’ 2X2 antenna array configurations with k-shaping. Excitation of coaxial modes has, for the first time, been demonstrated explicitly by analysis of the Poynting vector distribution in real space. An antenna configuration with a π-phasing in the z-direction (such that the radiated power spectrum peaks at k = 5 m^-1) and the choice of 3λ/4 long antenna elements with ‘symmetric’ excitation in the y-direction, are found to produce central RF power deposition profiles in the second- harmonic and minority heating of INTOR. Finally, from a comparison of results for circular and non-circular NET/INTOR plasmas with elongation k = 1.6, it is found that in the latter wave focusing is greatly reduced and that the power density figures are lower by approximately a factor of 1.9 for the case treated.