Lower Hybrid Antenna Design for MST

Inter-digital line antennas are being used to test the feasibility of lower hybrid current drive in MST. The antennas use !/4 resonators and launch slow waves at 800 MHz with n|| ~ 7.5. Routine operation has been achieved with a good impedance match between antenna and plasma. High power antenna design improvements include larger vacuum feedthroughs, better impedance matching, and rf instrumentation on all resonators. The antenna and feed-through modeling was performed with CST Microwave Studio. The pulseforming network that powers the klystron is being upgraded to a 50 kV – 30 ms pulse. The goal for the LHCD system on MST is a modular design that can handle 300 kW per antenna.