IBW experiment on JFT-2M tokamak

Abstract

Ion Bernstein Wave (IBW) is launched to the JFT‐2M tokamak plasma in order to investigate the coupling efficiency, the behavior of plasma heating, and the launching to H‐mode plasma. Plasma loading impedance increases as the separatrix approaches the IBW launcher, which indicates that the loading impedance increases proportionally to the edge electron density. Loading impedance with H‐mode plasma falls to about 40% of that with L‐mode plasma, mainly due to the drastic drop of the edge electron density. Enhanced impurity radiation is observed during IBW heating. The maximum launched power is less than 150kW, due to the enhancement of radiation loss which exceeds the launched power by a factor of two or three. In spite of radiation enhancement, increase of stored energy is observed by IBW heating. This is mainly due to the density build‐up, and the contribution from net plasma heating by IBW is small. H‐mode plasma produced by neutral beam heating is terminated by launching of IBW, which is considered to result from scrape‐off plasma heating. The threshold IBW power for H to L re‐transition is about 20kW.