Simulated effect of edge plasma density parameters on lower hybrid wave scattering in EAST

The incorporation of lower hybrid (LH) wave spectrum broadening in the poloidal wavenumber ( k theta) space at the last close field surface (LCFS) is reported to lead to better agreement of the modeled LH wave current profile with the experimental results [Baek et al., Nucl. Fusion 61, 106034 (2021)]. To further understand its underlying mechanism and find the possible influence factors, effects of wave scattering caused by drift-wave type density fluctuation on the probability distribution of the LH wave polar refractive index ( N theta ) at the LCFS are studied under density parameters in the scrape-off-layer. According to a scattering model [P. T. Bonoli and E. Ott, Phys Fluids 25(2), 359-375 (1982)], scattering probability and scattering angle distribution are two main factors that determine the degree of spectral broadening. Studies presented here show that the total scattering probability increases first and then decreases as the wave propagates toward a smaller normalized radius of poloidal magnetic flux ( rho). The degree of spectral broadening is found to depend on the density and density fluctuation together by changing the intensity and a proportion of the geometrical optics approximation term and the E x B drift term in the scattering model. Furthermore, the fluctuation correlation length can significantly modify the probability distribution of N theta at the LCFS, which is found to significantly change the LH wave current profile.

Automated summary

This study investigates the effect of density fluctuations on the probability distribution of LH wave refractive index at the LCFS in the plasma scrape-off layer. The results show that scattering probability and scattering angle distribution are the main factors affecting the spectral broadening. Additionally, the density, density fluctuation, and fluctuation correlation length can significantly modify the LH wave current profile.