The effects of E-r x B-t drift on LH wave coupling with divertor configuration at EAST

The coupling characteristics of the 4.6 GHz lower hybrid (LH) grill and the factors affecting LH wave coupling, mainly Er × Bt drift, with divertor configuration in anti-clockwise/clockwise magnetic field direction are studied. Based on the Langmuir probe measurement, the relationship between the reflection coefficient (RC) of LH power and the edge density at the grill mouth (ne,grill) measured by Langmuir probes is investigated. The optimum LH wave coupling with RC less than 2% is achieved when ne,grill is in the range of 1 × 1018 m-3–2 × 1018 m-3, which is quite close to the theoretically predicted value. In addition, the experimental results show that Er × Bt drift in the divertor scrape off layer plays a dominant role in affecting ne,grill and LH wave coupling. Studies show that the discrepancy in ne,grill and LH wave coupling in different magnetic field directions is mainly attributed to the different directions of Er × Bt drift, whereas the corresponding discrepancy with different plasma currents is mainly ascribed to the change in Er × Bt drift intensity. Therefore, for the upper single null divertor configuration, a lower/higher plasma currents is more favorable for increasing ne,grill and improving LH wave coupling in anti-clockwise/clockwise Bt. The above studies are of great significance for optimizing and improving LH wave coupling in the extension of the plasma operation regime.