Coupling Property Analysis of HT-7 Lower Hybrid Current Drive Phased Waveguide Arrays

Phased waveguide arrays on the HT-7 2.45 GHz lower hybrid current drive (LHCD) system are used to launch the waves into the plasma. Based on the two-dimensional linear coupling theory and the Step + Ramp plasma density profile model, the main coupling property of the launchers was investigated under different kinds of key plasma parameters, such as the edge density, the density gradient and the phasing between adjacent main waveguides. The analysis based on calculation shows that the wave spectrum ranges from 1.93 to 3.15 when the phase between adjacent main waveguides is changed between －90° and 90°. The global average reflection coefficient of the waveguide arrays is below 5% in the range of edge plasma density from 0.5×10¹⁸ m^-3 to 2×10¹⁸ m^-3, and the n_∥-weighted directivity is rather large. When the adjacent main waveguide phasing varies, the current drive efficiency of the launchers will be affected obviously.