Modeling very high electron heating by radio frequency waves on EAST*

In recent EAST experimental campaign, a very high central electron heating, fully-non-inductive discharge with the core electron temperature over 9keV has been achieved. Such high central electron heating was realized by injecting radio frequency waves, including 1.8MW lower hybrid wave (LHW) and 0.8MW electron-cyclotron waves (ECW). In this work, integrated modeling is performed to investigate the physical mechanisms of such high electron heating. The modeling confirms that the core electron temperature can be sustained around T_e≈5.5keV by LHW alone which is consistent with the experimental measurement. The electron temperature increases rapidly after the ECW is injected which is due to the interaction between the ECW and the electrons. With the increase of the electron temperature, the electron flux induced by the trapped electron modes (TEMs) and the electron temperature gradient driven modes (ETGs) is enhanced in the core region. The electron temperature increases slowly in a longer time scale. It is found that the slow increase is mainly due to the flattening of the density profile. Such flattening of the density profile can decrease the electron thermal diffusivity mainly induced by the TEMs, leading to a higher core electron temperature for a given heating source.