Experimental investigation of density behaviors in front of the lower hybrid launcher in experimental advanced superconducting tokamak

A triple Langmuir probe is mounted on the top of the Lower Hybrid (LH) antenna to measure the electron density near the LH grills in Experimental Advanced Superconducting Tokamak. In this work, the LH power density ranges from 2.3 MWm−2 to 10.3 MWm−2 and the rate of puffing gas varies from 1.7 × 1020 el/s to 14 × 1020 el/s. The relation between the edge density (from 0.3 × ne-cutoff to 20 × ne-cutoff, where ne-cutoff is the cutoff density, ne-cutoff = 0.74 × 1017 m−3 for 2.45 GHz lower hybrid current drive) near the LH grill and the LH power reflection coefficients is investigated. The factors, including the gap between the LH grills and the last closed magnetic flux surface, line-averaged density, LH power, edge safety factor, and gas puffing, are analyzed. The experiments show that injection of LH power is beneficial for increasing edge density. Gas puffing is beneficial for increasing grill density but excess gas puffing is unfavorable for coupling and current drive