Lower hybrid current drive profile dependencies on plasma current and density in EAST steady-state discharges

Lower hybrid current drive (LHCD) plays a crucial role in non-inductive current profile control in tokamaks; however, the key parameters governing its characteristics are not yet fully understood. On the Experimental Advanced Superconducting Tokamak, we conducted parameter-scan experiments combined with numerical simulations to investigate the effects of plasma current (Ip) and line-averaged electron density (n¯e) on the current profile peakedness, quantified by internal inductance (li). This study advances beyond the potential power deposition model [Zhai et al., Plasma Phys. Controlled Fusion 61, 045002 (2019)]—which offers initial theoretical insights but has inherent limitations—by employing self-consistent equilibrium reconstructions coupled with ray-tracing and Fokker–Planck simulations. Results show a clear transition from peaked on-axis current profiles (high li) at low Ip and n¯e to broad off-axis profiles (low li) at high parameters, with Ip exhibiting a stronger influence. Simulations validate the measured li trends and reveal that safety factor modifications drive the deposition shifts. Additionally, the trapped-gyro-Landau-fluid (TGLF) analysis [Staebler et al., Phys. Plasmas 14, 055909 (2007)] links the current profile to confinement properties, highlighting the role of electron heating. This work provides experimental benchmarks for LHCD optimization in steady-state operations.