Experimental quantification of lower hybrid current drive power on EAST

Quantitative evaluation of the lower hybrid current drive power absorption on EAST is critical for characterizing the confinement quality and for wave-model validation. While the high-density operation toward the high-performance regime may exacerbate parasitic edge losses, estimations of the effective power absorbed are not readily available. To evaluate the power absorption coefficient, α, a temporal modulation of the LH power of 1 MW is applied to the high-density H-mode plasmas (nebar = 4x10¹⁹ m^-3) with on-axis electron cyclotron heating. The rise and fall of the stored energy allows experimental evaluation of α by taking the approach in [V. Pericoli et al, PPCF 39, 1115 (1997)]. One feature observed is that the rise in magnetic energy (internal inductance) precedes the increase in thermal energy, implying fast electrons are produced in the on-axis region. Initial analyses show that α ≈ 0.5 (0.35) for the f_LH=4.6 GHz (2.45 GHz) cases. A phasing scan at 4.6 GHz yields a slight increase in α when the launched n|| is increased 2.04 → 2.48, consistent with the improved wave accessibility, but within the error bars. Further experimental data analysis and GENRAY/CQL3D modeling to examine wave propagation and absorption will be presented.