A Medium Power ECH/EBW Heating System for NSTX

Summary form only given. Electron Bernstein waves (EBW) are being investigated for plasma heating and current drive of overdense plasmas on NSTX. EB emission studies on NSTX have shown promising coupling results during some plasma edge conditions and are supportive of further work in high power heating and current drive. Additionally Electron Cyclotron heating (ECU) has several uses during under dense conditions such as plasma startup assist and coaxial hehcity injection (CHI) start up assist. A 3 MW EBW system has been proposed for NSTX and is awaiting funding due to the high cost of new gyrotrons. A medium power 350 kW 28 GHz system has been approved recently that will utilize existing gvrotrons and HV modulator/regulator equipment at ORNL and a HV power supply at PPPL. These gyrotrons may also be capable of operating at reduced power at 15.3 GHz in a lower order TE₀₁ cavity mode that will provide additional EBW coupling experimental capability. The launcher is a difficult area to optimize for EBW coupling with limited port area available on NSTX. Low power EBE launcher studies have provided good data on coupling efficiency when good antenna beam quality is available. A preliminary design for the medium power generation, transmission and launching system is presented in addition to results for gyrotron tests at 15.3 GHz.