Design of a PAM launcher and comparative analysis with the old FAM launcher for 2.45 GHz LHCD system on EAST

Abstract

In order to support EAST to realize the main mission of long-pulse operation lasting 1000s, the existing full active multijunction (FAM) launcher will be upgraded to a passive active multijunction (PAM) for the 2.45 GHz lower hybrid current drive (LHCD) system. The RF components were designed and optimized with consideration of the port size, power density inside the waveguides to avoid RF breakdown and power spectrum for efficient current drive. The designed PAM has a power handling capability of 4 MW CW at 2.45 GHz with matched load. The coupling properties and power spectrum were calculated using the ALOHA code and a comparative analysis with the old FAM was carried out. The main feature of this new launcher is that the density for optimum coupling and power spectrum directivity (ne ˜ 0.3 × 1017/m3) lies below the cut-off value (ne_co ˜ 0.74 × 1017/m3), which is favored for long-pulse steady-state operation on EAST. It has a capability to deliver 3.6 MW of power during real operation (ne ˜ 2 × 1017/m3) and 2 MW during large ELMs (ne = 10 ne_co). For the nominal phasing of 180 °s between modules, the power spectrum is peaked at N// = 1.8 and a maximum power directivity of 71.2% and reflection coefficient less than 1% can be obtained via simulations. Weaker hot spot phenomenon is expected with the designed PAM than with the FAM for their respective optimum densities. Finally, a thermal analysis was performed and the maximum temperature at the front of the antenna is expected to be ˜ 260 °C which is safe enough for operation. The PAM is scheduled to be installed on EAST in 2021.