Launcher study for KSTAR 5 GHz LHCD system

A 5 GHz Lower Hybrid Current Drive (LHCD) system with 2 MW is under development for the steady-state operations of the KSTAR. The present design of fully active waveguide launcher gives very good spectral directivity of more than 90 % for the phase shift of 90 degrees and a wider N_par; range of 1.4 to 3.6 with a width ΔN_∥ = 0.54. For the steady-state operations of the KSTAR, a Glidcop/SS sandwiched grill is proposed with consideration of heat and disruption loads. A PAM (Passive-Active Multi-junction)-type launcher is also studied for the possibility of use for the KSTAR. The PAM-type launcher provided good coupling properties even at lower edge densities in FTU 8 GHz PAM launcher tests. However, it gives a lower current drive efficiency compared with the conventional grill because of reduced directivities. The Passive/Active grill has 30 % less directivity than the Fully Active grill from the characteristic studies on the directivity and coupling. On the other hand, it gives a good coupling property with weak dependence on the phase shift between adjacent waveguides.