Electromagnetic analysis of the lower hybrid system of Tore Supra

The power division, in amplitude and phase, of the two Tore Supra lower hybrid antennas, is investigated. The system is composed by 120 power dividers and 128 waveguides facing the plasma. The main features of the antennas are given. The block diagram of the computing procedure is presented. Due to the low coefficient of reflection of the multijunctions, only one interaction is needed to obtain the exact power division. It is found that the inner rows of waveguides, with L1=180 degrees, have lower directivity for negative phasing than for positive phasing of the modules. It is found that: 2 rows of 32 waveguides, using the same type of multijunctions, excite similar N spectrum; and 2 rows with different types of multijunctions have different directivity. Due to the symmetry of the system, reflected fields recombining in the hybrid junction are close in phase and in amplitude. The coefficients of reflection toward the klystrons are ∼ 0.1%