Speaker
Haejin Kim
(KSTAR Research Center)
Description
Helicon wave coupling for efficient off-axis current drive using a traveling wave antenna has been proposed. It was found that helicon wave can drive plasma current in the mid-radius of high electron beta plasmas in medium and large size tokamak due to moderate optical thickness and wave alignment nature of helicon wave in helical magnetic field. KSTAR tokamak can be a good platform to test this current drive concept because it has adequate machine parameters. In 2015 KSTAR experiments, mock-up traveling wave antenna (TWA) has been designed using electromagnetic 3D HFSS. Mock-up TWA was fabricated and tested by using a vector network analyzer (VNA). After TWA installation at the KSTAR in 2015, wave couplings were investigated by measuring and analyzing reflection and traveling loss at port 1 and 2 of TWA using VNA. Preliminary results of couplings between plasmas and TWA were obtained in both L- and H-mode plasmas (shot 14190 and 14364), respectively. The coupling of 70~80% could be controlled by changing radial outer gap, the distance between LCFS and poloidal limiter at outer mid-plane, without severe degradation of plasma confinement. In order to investigate helicon wave coupling using high RF power, prototype TWA and high power transmission line system are under fabrication. During 2016 plasmas experiments, RF power from 4 klystrons generating 75 kW at 500 MHz will be combined using three 6-1/8 inch coaxial hybrid couplers and transmitted through coaxial transmission line of 10 m long. 500 MHz, 250 kW RF power will be fed into prototype TWA connected to 5 inch coaxial feeders through dual alumina disk windows. Design and RF test results of key components such as prototype TWA, coaxial hybrid combiners and dual disk windows will be presented. Preliminary experimental results for high power helicon wave coupling in KSTAR plasmas will be discussed.
Co-author
Haejin Kim
(KSTAR Research Center, National Fusion Research Institute, Daejeon, South Korea)
