Impact of rotated perpendicular wavevector of lower hybrid waves to lower hybrid current drive profiles on EAST and Alcator C-Mod

Standard lower hybrid current drive model generally predicts a broad power deposition profile with off-axis peaking, while experiments show on-axis peaking. In the present modeling study, spectral modification is introduced in an ad-hoc manner by modifying the initial orientation of the perpendicular wavevector, which may arise from wave scattering by turbulence in front of the launcher. The ray-tracing/Fokker-Planck solver GENRAY/CQL3D is utilized within the python-based πScope framework. The study finds that rotating the perpendicular wavevector in such a way as to increase the initial poloidal component of k_^ is effective in reproducing the centrally peaked current profile observed in monotonic shear plasmas on both EAST and C-Mod with an inclusion of radial transport of fast electrons. These waves can readily be absorbed to the central plasma, which reduces the sensitivity of the power deposition profile to a slight change of the plasma condition. Off-axis power deposition is reproduced in reverse shear plasmas. The results presented here suggest that spectral modification arising from edge density fluctuations in a tokamak may need to be considered in understanding wave propagation and absorption.