Understanding the parasitic effects of lower hybrid (LH) waves in plasma is essential for addressing the density limit issue in lower hybrid current drive (LHCD). LH power dissipation in the edge region on EAST is preliminarily investigated in an electron density ramp-up experiment through the measurement of the magnetic probe array (MPA). The components, i.e., fast wave (FW) and slow wave (SW), are first identified, and their power flux density is further estimated, suggesting the occurrence of mode conversion during wave propagation in plasma and showing a significant drop in FW power density with the increase in plasma density, respectively. Studies indicate that the sudden drop of FW power density is mainly ascribed to the power dissipation in the edge region due to high plasma density. To investigate the candidate for the power dissipation, the fraction of power dissipation (83%) is estimated by the power flux density, which is close to the complementary GENRAY/CQL3D simulated fraction of collisional absorption (CA) (70%), suggesting that CA is the main candidate for the drop of FW power density. Studies indicate that MPA measurement offers a useful and important tool for further investigation of wave component analysis and improving LHCD capability by understanding the mechanism of power dissipation in the edge region. More systematic analysis will be continued, including power dissipation induced by collision damping, parametric decay instability, and density fluctuations.
Cao et al. (Wed,) studied this question.